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  1. When a functional gauge is used for True Position, any difference the actual feature size is from the maximum material condition would be a bonus tolerance. . Symmetry can also be used in this case – but only if the slots have a referenced datum plane that they are symmetrical about (and measuring symmetry is very.:
    Whenever a geometric tolerance is applied to a feature of size, and it contains an MMC (or LMC) modifier in the tolerance portion of the feature control frame, a bonus tolerance is permissible. When the MMC modifier is used in the tolerance portion of the feature control frame, it Missing: pokies. Geometric Dimensioning and Tolerancing concepts are often difficult to grasp at first; beginners can have quite a difficult time understanding the basic principles. One of the reasons for this difficulty is the visualization problem of 3D concepts in 2D documentation. The goal of this blog post is to analyze the  Missing: pokies. GD&T is a system that uses standard symbols to indicate tolerances that are based on the feature's geometry. Sometimes called feature based dimensioning & tolerancing or true position dimensioning & tolerancing. GD&T practices are specified in ANSI Provides “bonus” tolerance. Ensures design, dimension, and.
  2. I understand the simplicity you used for the sake of explaining the concept, but otherwise, is there any practical reason to not set up the second hole to just have true position tolerance with extra bonus instead of a shift modifier? Also, I have a question on the 3rd and 4th pages I scanned. So when there is a datum modifier.:
    GDT Position Tolerance. Popular. GD&T True Position Tolerance By Claude Margaret. Using True GD&T: What is bonus tolerance? 7. By Ingemar II. ECM Webinar - True Position GD&T Basics GD&T Tip from Tec-Ease - Tolerance Those Slots Right By Willie Louie. GD&T Tip - Do Not Mix Basic and Toleranced. the actual hole size and the MMC hole size. The bonus tolerance is added to the specified position tolerance to determine the allowable tolerance zone size. the tolerance zone. The cylindrical tolerance zone is exactly perpendicular to the primary datum specified in the feature control frame and its true position is located. Datums and Features (con't) Features:Features: – Real, geometric shapes that make up the physical characteristics of a part. . (holes, slots, pins, tabs). If applied to features that This increased tolerance is called the bonus tolerance of the hole and changes as the size of the hole increases. Material.
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Wondering if you can help me out on this: The company I work for, one of their core manufacturing processes is laser cutting and subsequent press-brake air bending a secondary process that can be ignored for the sake of this question. The profile is a piece of cake, since it does not have to rely on predetermined datums.

Welcome and excellent question! Recall that, unlike profile, position requires the use of datum s. Also, keep in mind that without a datum callout, profile only controls form. Note 1 always calls out material, Note 2 always calls out finish etc. This document could then specify for certain types of features which datums to use with a position tolerance in the drawing title block.

This route seems much more fraught with complications and opportunities for mistakes, however. Thank you Matt, definitely some food for thought here! Problem is, our parts are not defined by basic dimensions, but rather the CAD file itself more specifically, a DXF that is generated from the 2D drawing. Our flat parts are complex enough that full dimensioning is not practical not to mention unnecessary , but I still want to convey a certain dimensional expectation, based on the CAD file, not basic dimensions.

It would have to control not only the surface profile of individual cutout features, but also their location. Bill — I think you are most of the way there. This drawing does not fully define the product. The model does not fully define the product. All dimensions obtained from the model are to be considered basic. Define all datums used in feature control frames 2. Specify on the drawing controls for all critical features or those that mate with other parts 3. Callout controls for all threaded features studs, tapped holes, helicoils, nutplates etc.

Things like chamfers, radii, non critical holes, diameters, skin thicknesses etc. The important point here is that there are no dimensions or tolerances called out in the model. This may not be the optimal way to do it, but it seems to work for us. Grab the bull by the horns Bill, be the agent of change. Datum A is the OD of tube.

How do I figure tolerance zone of Basic angle from a Dimensional callout? I am using an Optical Comparator to inspect. Datum A as you have it defined for your part is the central axis of the tube. Your hole is located at a theoretically exact angle from this center line of Note that the theoretically exact centerline of your line intersects with datum A. It is about this theoretically exact line that the diametral tolerance of. As for inspection with an optical comparator what comes to mind is to place a gage pin of appropriate diameter in the hole and then place them both in the comparator.

If your drawing is dimensioned how I think it is with an angle and an off-set distance you should be able to verify this on the comparitor. You would treat it the same as you would with orthogonal thru holes in a flat plate. This should at least give you a few ideas of which direction to head down.

I hope this helps, let us know what you actually end up settling on. We want to keep the forums here healthy and active with useful information. Yikes, delving into some more complicated material here. First, in the standard the terms Inner and Outer Boundaries are done away with.

The symbols circle M and circle L , application and interpretation of the meaning remain the same between the and standards.

What they allow for is: The use of fixed functional gages. Imagine a circular part. Your datum feature simulator for datum A has a diameter of 9 MMB size.

Your functional gage to verify location of the smaller holes would have pin diameters of 2. Your gage would look like the negative image of your part, i. Without the MMB callout, you would have to reject the part. With the MMB callout you are able to move the part in the gage to hopefully get your part to fit not always possible as the center hole of the part departs from MMB to LMB.

However, if the part center hole is produced at 11 you have 1 of float in any one direction to get your part to fit. You are in effect re-centering the axis of the part.

Caution, if you have features opposed to one another that wander in opposite directions, no amount of float over the gage is going to get you into a fit condition. It does get a little bit more complicated than this as you must respect controls of higher precedence datums.

However, this should allow to get a better grip on the situation. I hope this was clear. Let me know if we can be of further assistance. Thank you Matt, I need the formula to convert the. My way of thinking is it would be easier to know zone, angle wise verses Decimal wise. That tolerance zone is inclined by your basic angle relative to your datum A. No matter how far off from true position you are.

As long as the axis of your manufactured feature is entirely within this zone the part is good. I think you are asking how much variation in angle is allowed via this diameter tolerance zone. If this is indeed the case, some straightforward geometry should do the trick.

The variation angle depends on the size of the tolerance zone and the wall thickness of the part. A thicker wall is going to restrict your variation in the same manner a tighter tolerance zone would. Check my math here as I did this on a napkin. For a tolerance zone of d, at a basic angle of I assumed a wall thickness of.

Yes, that is perfectly legal. We do it all the time. I have a customer part, where, their drawing calls out true position on the bore of a Round Single Bore Tube. The call out is. All examples I see are typically a cylindrical feature, hole or boss, on an otherwise linear planar part.

Anyone have advice or seen this kind of usage of true position before? The specific application that appears to be going on here is for positional tolerancing of coaxial features of opposed diameters. Datum A is the flat face of the part, this is the start of the universe for this part. From there the outer diameter, datum B, is constructed.

Now, with datum A defined and datum B defined relative to datum A we locate the inner diameter with a diametral tolerance of. Why have datum A as the flat surface and why have it called out first? My guess is that the end of the tube mates up against some other feature at a higher level assembly and it is more important for the inner diameter to be perpendicular to this surface than it is to be located relative to the outer diameter.

Any number of applications for parts could fit this bill. Remember, datum selection is based upon functionality at assembly. What mates first, is there a sequence of assembly that matters etc. I think your asking how to go about calculating the actual position of a hole versus the drawing requirement?

This formula should clear up any issues. This will produce a diametral positional tolerance that you can compare against the drawing requirement. If your calculated tolerance is larger than the one specified you are not in spec!

The bonus tolerance is equal to the the amount of departure from MMC of the considered feature. This gets added to the tolerance value stated in the feature control frame. It has a positional tolerance of. For the purpose of our example locate your X,Y Cartesian coordinate system at the bottom left corner of the plate.

In a perfect world the axis of the hole would always be located at 1, 1. In reality there are always sources of error that prevent this from happening. You get the part in house and use a digital coordinate measurement machine to determine the actual location of the hole as 1. Is the part good? How do you figure it out?

Delta X and Delta Y represent the difference between the actual measured location and the basic location. The position requirement was. Thus, this part must be rejected. I highly recommend going through some of the other comments in the true position forum as there are some other really good examples I have put up there. I am having a hard time with this. How can a square with a size of 0. To me the square box has a larger tolerance zone.

Though I know that two parts will not fit together the same way, or at all. I can easily clear up your confusion. Take a piece of paper and draw a perfect square.

Now, over the square draw the smallest circle you can such that the corners touch the edge of the circle. Label all sides of the square The area of the square is If I asked you to calculate the area of the circle how would you proceed? Where r is the radius. The point at which the square intersects the circle i. Plugging this back into the circle area formula we get — 3. This person gathered like minded individuals and started developing commonly accepted standards that eventually evolved into what we know as ASME Y I understand your explanation but have one question.

If the true position without a diameter call out is 10….. To me this should be Ah, in this case you are referring to a feature of size other than a circular one. In that case you are controlling the center plane of the toleranced FOS a tab or slot as determined by parallel surfaces of the FOS. The tolerance value represents the total distance between two parallel planes. Sorry about all that, my previous explanation was bit long winded.

For further information refer to Section 7. Let us know if you need any more help. Machine shops or metrology houses will have a digital Coordinate Measurement Machine CMM that does all the work digitally. There is a small spherical diameter ball or probe on the end of an articulating arm that is hooked up to a machine with special software.

After locating datum surfaces the hole position can be compared against the datum structure and ultimately the drawing. A fixed functional gage. If a part has a high quantity manufacturing run it may make sense to use a fixed functional gage. The hole size would have to be verified separately. The gage for say, a block with a hole in it, would be one that simulates the referenced datum structure in your case A at MMB and B at MMB with a pin at the virtual condition of the hole and located relative to the datum structure.

If the block fits over the gage, then the position requirement is met. Through the use of a special set of calipers http: How is this done? The drawing calls out basic dimensions or should these are theoretically exact dimensions. The formula for calculating the actual positional tolerance to compare against the requirement is: Delta X and Delta Y represent the differences between the manufactured distance from a datum and the basic theoretically exact dimension.

This could be done with a regular set of calipers without the cylindrical tip shown, but your accuracy will suffer greatly. An alternate way would be to specify the axle of one wheel as a datum and have the axle of the wheel that is intended to be co-linear with it controlled using runout.

As for using positional tolerance I would refer you to section 7. This section addresses the capability to control coaxial positional tolerances through the use of composite positional tolerances. In particular, Figure 7. It shows coaxial holes, but the concept also applies for external features of size.

If the hole position is controlled by just 2 datums A and B in this case at what cross section along the hole would you use for measuring to determine whether its within tolerance?

For example, if you had a crooked hole, if you measure on the surface its good, but on the bottom its off. With a 3 datum setup you can control this.

Just wondering for a 2 datum setup how would work. All parts of the hole axis have to be within the tolerance zone defined by the feature control frame with respect to your datum reference frame. In the above example, if the hole position was just controlled with respect to only datum A and B would the tolerance zone still be a cylinder? Wouldnt this be the same tolerance zone if the hole were controlled with respect to A, B, and C? Not sure what the difference would be between controlling hole position with 2 vs 3 datums.

The sequence of the datum reference frame A-B-C or C-B-A etc is telling the inspection department in which order to set up the part on the inspection table. To begin measurement the primary datum comes in contact with the datum feature simulator, followed by the secondary and finally the tertiary. There is no set rule as to what your datum sequence should be, it really depends on your part and your assembly and what you view as the most important.

Now, with that being said, for flat parts it is normal to see the surface perpendicular to the hole as datum A, with datum B as the longest edge surface for stability on the inspection table and datum C as the next longest edge surface. You have to be able to basically theoretically exactly locate your feature of size relative to your datum reference frame.

With this bit of information you should be able to infer that you would need at a minimum of 2 datums in this case B and C to properly locate the FOS. All of your tolerance for your FOS comes from the feature control frame. Or do I have to calculate the true positional tolerance formula in order to know what distance I can have against the Datums?

Could you elaborate, please? Hello — When you have a cylindrical tolerance zone as indicated by the diameter symbol that means that the tolerance zone is located exactly where the basic dimensions place it. The axis of the feature must remain within this zone but is otherwise free to move anywhere within it. We delve into a grey area. Simplistically, for a flat rectangular part in order to be fully constrained there needs to be 3 datums.

These datums are essentially telling you that from your datum reference frame the axis of the hole is located theoretically exactly basically from two edges and theoretically perpendicular basically to the primary datum.

Obviously, this changes when you start dealing with cylindrical parts. Every dimension and callout must have a tolerance in order for the part to be produced. The feature control frame is describing a cylinder in which the axis of the part can vary this produces your tolerance. It can be a tricky subject and the more you deal with it the more sense it will make. Let us know if you need any additional clarification.

I would be happy to understand if my reading is wrong. In this particular example the designer is specifying that the edges are of more critical importance than the back flat surface.

Remember that the order of datums is specifying the order in which the part comes into contact with the inspection equipment. In this particular case it is specified that first one edge, then the other, followed by the flat surface are to touch the inspection equipment. Hi, I was wondering if it is possible to apply a percentage tolerance to true position. To further complicate things there is also a bleed tolerance where the ink will bleed out from the printed image and this is typically constant regardless of feature size.

You might look into that avenue. Your application of positional tolerance to an ink-jet image is a new and intriguing one for me though! The only time you should come across the discussion of radial tolerance is in a tolerance stack, i.

You will only ever find the diametral or spherical diametral symbol prior to the tolerance in the feature control frame when they are required. I want to ask whether the position tolerance on a feature of size can be more than the total size tolerance on that feature of size.

Is there any explanation? Absolutely, there is no restriction on the tolerance with regard to the position control. It is only with the form controls that are governed by Rule 1 MMC at perfect form that require that the tolerance be smaller than the size tolerance, i. For form controls this is the case unless: I am working on a drawing 2d to 3d and on there are two values of lmc and mmc for holes for eg 2.

All help is appreciated. Are these mmc and lmc values or are they something else? What you are seeing is just one of the ways to represent a tolerance. Every dimension must have a tolerance and the different ways allow the designer to convey intent. If I were to put the dimension of a hole down as 2. The designer is indicating that he wants a hole of diameter 2. The same applies for unilateral tolerance i.

The case that you illustrate is known as limit dimensions where the absolute limits of size are indicated. In this scenario the designer is indicating the limits he can live with but is expressing no preference for size. As a CAD drafter or machinist I would split the difference when producing the hole so as to reduce the chances of having a part rejected i. If I had two plates with holes in an array, what control features would I use to ensure the plates are always aligned?

After reading up on this a little it seems like a true position diameter tolerance with an MMC condition referencing the same datums A, B, and C you did in both examples would be the way to do it. Am I correct in that thinking? Hello Patrick, You are absolutely on the right track — Great work! I wish I could go into more detail about it here in the comments, but I may add this lesson as a free video for the site in the near future, since it is such a common application of Position.

They do represent datums, but not always flat planes. What that datum structure in the feature control frame is telling you is the sequence in which the part must contact the inspection equipment. It is saying that first the part must be in contact with datum A, then B and lastly C.

Can datum A control spatial? Can Datum A control plane rotation? Can Datum A control X,Y? Can Datum A control Z? Ok now on to Datum B, what is left to control?

Can Datum B control Spatial? Can Datum B control Planar rotation? Now to Datum C. I have seen countless Datum schemes and the feature types are mixtures of planes, cylinders, spheres, torus, etc… The inspector must follow the order listed. They are very different simply by the order of the letters. Hi, would you be able to answer my question below? If I have a plate with datum A B C being the base and edges.

There are 2 holes in the plate. I require hole 1 to have a true position of 20mm with a positional tolerance of 0. I also want hole 2 to be positioned 10mm from hole 1 within a positional tolerance of 0.

If the actual position of hole 1 ended up being Could this be achieved by chaining the dimensions between hole 1 and hole 2 similarly to what you have shown in example 1, only referencing datum ABC? Or would I need to make Hole 1 a separate datum D, and reference datum D in the positional tolerance of hole 2?

The best way to go about doing this would be to change your datum structure so that hole 1 is datum D and hole 2 is then referenced off of that. The formula you quote is for determining the diametral tolerance zone, you should not be dividing by 2. This way you can directly compare against the requirement stated in the field of the drawing. Let us know if you have any other questions. I have hole position: Y Basic is symmetry. Without the diameter symbol, how would you Calc TP? I think you may be mixing a few concepts together.

Dear Team, I want to control all around form of the part which is plastic and it is going to be chrome plated. How I can define my tolerancing scheme without datums. Just in a note or by giving some presentation.

Recall that if no datums are called out a profile control is only controlling the form. We use a similar note all the time at my company. Hello, We have a disagreement between a few of us on how to interpret the call out on a print.

We have a round pin the will have a hole drilled through the OD which is datum A. There is a basic dimension from the face on one end of the pin which is datum B. Both dimensions have the diameter symbol in front of them. Our issue starts as one inspector claims we are only allowed the. A few of us disagree and feel as long as the two dimensions jive, and say within a figured tolerance pe the formular for X and Y coordinates, then we have acceptable parts. Can you please clarify as I fear we have been scrapping good parts.

For the AB position I would say that at any point along the hole axis it should not deviate from the basic by more than 0. For the A position I would say that at any point along the hole axis it should not deviate from the A datum axis by more than 0. The diameter symbol in these cases of no datum C can seem to be applied wrong, but they are actually controlling perpendicularity and position, which is why I noted at any point along the hole axis.

The diameter zone of 0. I get quite a few drawings from one Company in particular that have a hole position datumed off the face it is drilled through, there is no reference to directional tolerance, only the face that it is on. If a is the face of the paper, how do you work out the positional on a face? If the position is on a pattern, the requirement is simply to the pattern itself not any other feature on the part, Otherwise it is simply a perpendicularity tolerance.

Surely then, if it is just a single hole a perpendicularity symbol should be used to indicate that a cylinder measurement is required. If the part is a thin piece like paper thats not possible so would the positional tolerance meaningless?

The perpendicularity still would theoretically exist, but may not be functionally necessary. You would still have to position the hole though in space and that is where Position will be important. I have japanese drawing, where a nut is welded over a pierced hole. The position tolerance has LD written above it. I guess it stands for Lower Deviation, and it is a modifier for Feature of size, but I do not know how does it affect the calculation of the tolerance field. If it affects… 2xM6 LD pos.

Yes, I was reading incorrectly. Total allowable tolerance would be callout tolerance plus bonus tolerance. Basic dimensions, how are basic dimensions recorded on a inspection report? Do you ignore them? Do you record actual valves? Do you just list the nominal? Do you list the True Position that they control? Both the length and width are designated separately, and both have the same DRF. Is there anything special I should consider with this symbol? Err… maybe more generally what should people keep in mind when a slot IS a datum and not referenced to one?

Yes I know one is the box on the print and the other is the mating envelope that designates the Datums. There are numerous free tutorial sites but most act like they are tutoring an engineer who should not need the tutoring any way.

I have a test this coming week for a quality control position I applied for. I especially like the symbols laid out so one can click on them and get a thorough explanation of the meaning and application of it. I have years of experience as a web designer and that pops out as brilliant to me. It has been years since I took courses in drafting and design and this site made for a good memory refresher.

Thank you so much! We enjoy working to continue keeping this content up to date and really appreciate that you are learning from it. We want to make sure we help as many people as possible with this often over-complicated topic.

Good luck on your interview! The inspector reports that the characteristisc is. How should I interpret this. Is this reporeted disprepancy is the distance from the center? Thank you in advance for help. Reported position tolerance is always in diametric size. Im learning a lot from your site. As i gain knowledge the more question pops up on my head. Can you asnweer me please. I have a hole mmc positional tolerance of 4thou, to check it im using a checking fixture.

Now as we know fixture has tolerance also since we can not do perfectly as 0, 0. The part is located and fixed on datums on the fixture. How i would be able to decide for the location tolerance of my checking pin on the fixture?

Hello Mark- your basic dimensions are the location of these checking pins. Remember measurement equipment is theoretically perfect, however, you would need to look up the applicable gauge tolerance. The standard ASME y Should the symbol of datum A triangle be changed to point downward? There is nothing in the standard that dictates which way the symbol the triangle should be pointing. The intent is clear that the bottom surface represents datum A.

Sometimes stuff just fits together better the other way. Hello, first of all thanks for your contribution! I was wondering if the reference system is defined by the datums or by the exact dimensions. For example, in a case where the datums A and B are not perpendicular, but the exact dimensions are so. What if the plate was trapezoidal and the datum A and B were not perpendicular.

If I consider that plate with the datum A as it is horizontal and the datum B with an angle with its own exact dimension. I could still put the two exact dimensions 30 and 20, plus the angle. Thanks for your answer. As an example you could have a typical parallelogram with the flat face as your primary datum and your two edges as secondary and tertiary datums. It does nothing to change how the concept of basic dimensions or tolerance zones work.

In this case, however, you would need to dimension everything directly back to the vertex i. The way to handle this on a drawing typically is to use a basic angle and a basic dimension to your feature. Step one when reviewing or creating a drawing is to locate your datum structure. All features using geometric tolerances that call out those datums must relate back to them. I have a question. Imagine a 50mm x 50mm square plate with four 5mm holes in a centred square pattern say 10mm from and edge and 30mm between centres in both directions.

Now consider the tolerances. I want the holes to be in true position in relation to one another within 0. The position of the holes with respect to the edges of the plate are of little importance to me, say the entire hole pattern could be located with tolerances of 2mm with respect to the edges of the plate. I am not sure how to specify this tolerance on the holes in a drawing, particularly the internal relationship between the holes.

True position requires a reference. What reference do I choose? You are describing a classic example of a composite positional control. For a composite control you have two segments feature control frames one directly above the other , only the position symbol is entered once and the height of both feature control frames. The tolerance for the upper control frame can be large, as you suggest 2 mm, keep your datum structure as A, B, C.

Then for the lower segment enter 0. It can get a little more complicated depending on whether you want the pattern oriented a particular way, or basically located from one of the datums. Otherwise you are good to go. True Position —Location of a Feature Position in terms of the axis, point or plane defines how much variation a feature can have from a specified exact true location. True Position —Location of a feature A 2 dimensional cylindrical zone or, more commonly a 3-Dimensional cylinder, centered at the true position location referenced by the datums.

True Position —Location of a Feature True position of a feature is made by first determining the current referenced point and then comparing that to any datum surfaces to determine how far off this true center the feature is.

Note on Bonus Tolerance: True Position —Location of a feature True position is closely related to symmetry and concentricity as they both require the location of features to be controlled. True Position —Location of a feature In example 1 you can see how a hole can be called out using true position. True Position —Location of Hole Example 1: The True position callout on a block With true position called out the holes do not need to be in exact positions as shown below, but their centers can vary by the amount specified by the tolerance.

Same specifications This would be the go gauge that would measure for hole size, orientation and position. Top view of the part once inserted into pin gauge As long as the gauge can go into the part, it is in spec. Bonus Round Remember the further you are from MMC when it is referenced in the feature control frame, the more bonus tolerance you are allowed.

Profile of a Surface Link Enlarge. Total Runout Link Enlarge. Profile of a Line Link Enlarge. May 6, at 2: May 6, at 8: May 12, at 1: November 4, at 1: November 18, at 8: November 7, at 9: July 28, at 7: August 3, at 2: September 6, at 2: September 6, at September 21, at May 18, at 1: May 20, at 7: May 19, at May 22, at 9: May 22, at May 26, at May 27, at 9: June 17, at 4: June 17, at 6: June 29, at 1: June 29, at 4: June 29, at 5: June 30, at 4: July 15, at July 18, at August 6, at 5: July 28, at 5: December 24, at 3: August 6, at 1: August 16, at 9: August 21, at 4: September 4, at 9: August 26, at 7: September 3, at 7: September 29, at 5: September 17, at 4: September 29, at 8: September 30, at 7: October 2, at 8: October 6, at 3: October 16, at But, it seems that since Figure shows two coaxial diameters, someone at your place thinks this is only a special case for coaxial diameters.

The two diameters could just as easily be side by side with a basic dimension other than the implied basic zero dimension separating them. I hope this helps. It kind of looks like they are calling out datum targets as datum features of size at Maximum Material Boundary. Someone has gone beyond what Y It just could have been done in a more conventional manner.

Also, I understand why we give X, Y and Z dimensions for the axis location of tubes. But, giving X, Y and Z separate tolerances that are all the samenumber is odd.

Why not just give it a position control with a diameter of 4 millimeters that confines the axis of the tube. Here is an illustration from one of my textbooks: Datum Feature Shift Hello Mr. I am looking at a tool drawing someone designed with the second hole referenced to the first hole with a datum modifier MMB and a 3rdhole referenced to the 2nd hole at MMB. I have attached a scan of a page from your book 1st and 2nd scanned pages. I understand the simplicity you used for the sake of explaining the concept, but otherwise, is there any practical reason to not set up the second hole to just have true position tolerance with extra bonus instead of a shift modifier?

Also, I have a question on the 3rd and 4th pages I scanned. So when there is a datum modifier, should I always consider the datum feature to shift with the type of tolerance in the original reference frame, like perpendicularity in the 3rdpage. I have seen some explanations from others that made it seem as if you took your example, it would be looked at like a positional shift no matter if it originally referenced something like perpendicularity.

Best Regards, Joey The pages Joey scanned from one of my books: Granted, there are some isolated cases where this strategy might work out, but many more cases where it will not. Certainly, for a pattern of holes referenced to a datum regular feature of size such as one hole , as the datum regular feature of size departs from its virtual condition Maximum Material Boundary concept , that pattern of holes may shift as a group an additional amount.

This apparent shift of the pattern of holes is actually a movement of the datum feature axis away from its imaginary datum axis. This concept is thoroughly explained in other sections of this book. The planar primary datum will serve the purpose of perpendicularity control, while the secondary datum feature will be a hole which generates an axis that will be used to hold a millimeter distance. So, datum A will be for perpendicularity and B will be for location in the following illustration.

FIGURE [Part Drawing] In the simple example depicted below, the following illustrations show correct distributions of the tolerances that would allow parts to pass the gage. In reality, they are quite different. In Example 1, the shaft axis is controlled for perpendicularity within a diameter of 0. As the shaft departs from MMC is made smaller, but still within size limits , the tolerance zone will grow to permit a maximum out-of-perpendicularity of the axis to datum plane A of a diameter of 0.

Datum feature A has not, in this case, been controlled for flatness. Datum plane A is taken from the high points of the datum feature. That surface must be within two parallel planes 0.

All elements of the controlled feature bottom surface of the part must lie between these two parallel planes. This controlled feature is not only controlled for perpendicularity but also for flatness to within 0. Since the surface being controlled by perpendicularity is not a feature of size, it is not allowed to be modified with the MMC symbol. The flatness of the surface is controlled to within 0.

This means that as the datum feature departs from its MMB is made smaller than The two parallel planes 0. This has the effect of increasing the allowed out-of-perpendicularity; but at the same time, the flatness of the controlled feature is held to within 0.

When you have one hole positioned to another, it is like saying that they work together, for example, they mate with the same part. If they mate with the same mating part, the MMB modifier used with the MMC modifier in the same control, is a way of saying that if either hole deviates from its virtual condition, the holes may deviate more from being perfectly positioned to each other. The larger the hole without being more out of perpendicularity to a planar primary datum , the more each hole may move away from the basic dimension that connects them.

Picture a gage with two virtual condition sized gage pins on a plate, one for the datum feature referenced at MMB and the other for the hole being positioned. As each hole grows without being made more out of perpendicularity to the primary planar datum , that hole may move more before it hits the gage pin. Or, as each hole grows, it may be more out of perpendicularity to the primary planar datum.

Or, a little bit of both, but no more than the gage pins would allow. In that instance, the gage pin simulating the datum feature would have to expand into the hole, locking it up, and allowing no shift. There is quite a bit of difference between angle and location. Position controls both angle and location, but perpendicularity controls only angle.

So, the shift on a perpendicularity control that references a datum feature at MMB would only allow an angular shift zone, since the relationship being controlled is only one of angle not distance. I am still a little confused on the second concept I brought up and you explained, but this figure I attached actually illustrates my problem better than what I tried to use.

For the hole on the right, does the datum modifier of -B- at MMB represent added positional shift being in the original Datum Reference Frame of the feature datum or perpendicularity shift since that is what -B- has as a tolerance type of the feature datum?

That one is positional shift. The relationship between the second hole being positioned and the first hole which is what the second hole is being positioned to is one of location. So, as the first hole datum feature B grows from 49 toward 50, the second hole may shift away from the datum axis of B by the growth of B. Any out of perpendicularity of datum feature B negates the shift it allows as it grows. The theory, as explained in Y The theory is that as datum feature B grows, its axis may shift away from the imaginary datum axis B.

This is pretty easy to visualize, if you picture the gage I described with two pins on a plate. The first pin axis simulates datum axis B. If the hole B is larger than the gage pin virtual condition , the hole B axis may shift away from its own gage pin axis. So, to someone holding the part in their hands, it will appear as if the second hole has shifted away from its perfect location from the first hole. But, the theory is that it is the first hole that has shifted.

The axis of hole B datum feature B has shifted away from the imaginary datum axis B simulated by the axis of the gage pin. Runout and Free State. I hope you are doing well. I have taken a couple or your classes in Huntsville, AL, and I would like to get your input on a of couple questions, please.

As I understand it 6. Figure p seems straight forward with respect to free state, however, Figure leaves me with some questions. Thank you for your time,. Yes, the runout controls in Figure are free state measurements. All measurements are free state unless a note is written to specify they are to be restrained while measured.

the same time spend

However if you are locating a hole where a hose or wire must go through. You may have a tight fitting tolerance but a fairly loose position tolerance. The image for the formula comparing true position and actual position is confusing. The formula makes sense if the goal is to get the distance of the positions by getting square root of x and y coordinate differences.

The correct formula is 2 times the square root of the distances. Yes, that is precisely correct. Draw your Cartesian coordinate system, place a 2 x 2 square at 0,0. Now, draw a circle that circumscribes the square with a center located at 0,0. The circle should only contact the square at the 4 corners. Thus, half the diagonal of the square from 0,0 is equal to the radius of the circle. To get the diameter you multiply the Pythagorean theorem by 2.

Pardon me but drawing a square centered at 0,0 and the diagonal distance and circumscribe it with a circle is just muddying the waters. In far simpler words, the TP tolerance defines the diameter of a circle centered at 0,0. The actual center of the feature must be within the circle. The distance from 0,0 to the actual feature center must be equal to or less than half of the given TP tolerance value.

I have a customer that requires true position of a diameter on an end of a shaft from datum A which is a different diameter on the other end of the shaft. The datum and the diameter feature are considered theoretical centerlines correct? And measured as such RFS? Should this requirement be shown best as a true position call out or concentricity or maybe runnout?

Position could be the correct way as it would ensure that the axis of the diameter feature is coaxial to the datum axis within the position tolerance diameter. Runout and Concentricity are more than just making a part coaxial. Runout would be controlling the coaxiality and the circularity of the diameter feature. Concentricity is also controlling coaxiality but it making sure that the form of the diameter is evenly distributed. Runout on the other hand would be useful if the diameter feature was rotating and making contact with another part.

Runout is called a combined control because it can control the position of the axis coaxiality but also control the form circularity. The only thing you might want to add is a definition of the floating datum system, there TED theoretically exact dimension is only indicated between two or more features without any reference to datum.

In this case you must not use datum letters in tolerance definition and none of the relative degrees of freedom between TED and rest of the part is locked. Yes that is true — Position does not require datums if you are trying to align a theoretically exact dimension on something like a coaxial shaft.

Hello everyboby, I have a question. What is a tolerance zone when the true position is within diameter symbol? May be the form of tolerance zone is square? In the ISO I have many cases in my everyday practice us metrology specialist.

This cylinder is located at the basic dimension location. If you calculate the X,Y coordinates away from the True Position, you would get your limit, however it would be the radial distance away from the center. Since Position is measured as a diameter you need to multiply by two to get the equivalent Position tolerance. Even though you are only 0. One side wall is Datum B and have a hole at 1. The true position call out is. Something like this would be fairly hard to measure without any computer based measuring.

For the Datum AB top the design intent allows for a functional gauge to be used since the MMC symbol is used This would mean you would Setup a fixture to secure the pin and go perfectly center at datum A, and then butt up against datum B. You would then take a gauge pin at this exact location centered to datum A and 1. For the second position callout, you would secure datum A, but not B.

You would then have a gauge pin secured exactly center. This gauge pin would be at the hole size — 0. If you want to know more about functional gauging we cover this in our fundamentals course. Learn more at https: But how to measure it without CMM? I have a PCD of 76mm dia for threaded hole M6 with position tolerance 0. How can i measure this without CMM. Threaded holes are a gray area for functional gauging.

However to truly ensure that the pitch is located correctly requires the use of a more advanced setup. Thing is about true position with two datums. But these datums are paraller to each other. Round part with a eccentric hole. The datums are the outer diameter and the eccentric hole. Mikko — Sure, send it along. Did it bounce back? I hate doing something on blind faith. It helps when I understand why I am doing something. True position is the diametric zone that the axis of the part should like within.

Since it is a diameter it is dual sided and the formula needs to divide by 2 to go from a radius to a diameter. I hope you are finding the website material helpful in your studying. I have a copy of the ISO standard and it appears that when you have a positional tolerance without the dia symbol applied to a circular hole, you are able to control the tolerance in two directions that are orthogonal to one another.

The tolerance zone in the feature control frame is telling you that the extracted actual median line of the hole must be contained within two pairs of parallel planes positioned apart by a distance equal to the value of the tolerance in the direction specified and perpendicular to each other. Both pairs of planes are oriented relative to the datum reference frame and symmetrically disposed about the theoretically exact position of the considered hole.

I hope this helps. Hello, and thank you for this awesome resource! Wondering if you can help me out on this: The company I work for, one of their core manufacturing processes is laser cutting and subsequent press-brake air bending a secondary process that can be ignored for the sake of this question.

The profile is a piece of cake, since it does not have to rely on predetermined datums. Welcome and excellent question! Recall that, unlike profile, position requires the use of datum s. Also, keep in mind that without a datum callout, profile only controls form.

Note 1 always calls out material, Note 2 always calls out finish etc. This document could then specify for certain types of features which datums to use with a position tolerance in the drawing title block. This route seems much more fraught with complications and opportunities for mistakes, however. Thank you Matt, definitely some food for thought here!

Problem is, our parts are not defined by basic dimensions, but rather the CAD file itself more specifically, a DXF that is generated from the 2D drawing. Our flat parts are complex enough that full dimensioning is not practical not to mention unnecessary , but I still want to convey a certain dimensional expectation, based on the CAD file, not basic dimensions.

It would have to control not only the surface profile of individual cutout features, but also their location. Bill — I think you are most of the way there. This drawing does not fully define the product.

The model does not fully define the product. All dimensions obtained from the model are to be considered basic. Define all datums used in feature control frames 2. Specify on the drawing controls for all critical features or those that mate with other parts 3. Callout controls for all threaded features studs, tapped holes, helicoils, nutplates etc. Things like chamfers, radii, non critical holes, diameters, skin thicknesses etc.

The important point here is that there are no dimensions or tolerances called out in the model. This may not be the optimal way to do it, but it seems to work for us. Grab the bull by the horns Bill, be the agent of change.

Datum A is the OD of tube. How do I figure tolerance zone of Basic angle from a Dimensional callout? I am using an Optical Comparator to inspect. Datum A as you have it defined for your part is the central axis of the tube. Your hole is located at a theoretically exact angle from this center line of Note that the theoretically exact centerline of your line intersects with datum A. It is about this theoretically exact line that the diametral tolerance of.

As for inspection with an optical comparator what comes to mind is to place a gage pin of appropriate diameter in the hole and then place them both in the comparator.

If your drawing is dimensioned how I think it is with an angle and an off-set distance you should be able to verify this on the comparitor. You would treat it the same as you would with orthogonal thru holes in a flat plate.

This should at least give you a few ideas of which direction to head down. I hope this helps, let us know what you actually end up settling on. We want to keep the forums here healthy and active with useful information.

Yikes, delving into some more complicated material here. First, in the standard the terms Inner and Outer Boundaries are done away with.

The symbols circle M and circle L , application and interpretation of the meaning remain the same between the and standards. What they allow for is: The use of fixed functional gages. Imagine a circular part. Your datum feature simulator for datum A has a diameter of 9 MMB size. Your functional gage to verify location of the smaller holes would have pin diameters of 2. Your gage would look like the negative image of your part, i.

Without the MMB callout, you would have to reject the part. With the MMB callout you are able to move the part in the gage to hopefully get your part to fit not always possible as the center hole of the part departs from MMB to LMB.

However, if the part center hole is produced at 11 you have 1 of float in any one direction to get your part to fit. You are in effect re-centering the axis of the part. Caution, if you have features opposed to one another that wander in opposite directions, no amount of float over the gage is going to get you into a fit condition.

It does get a little bit more complicated than this as you must respect controls of higher precedence datums. However, this should allow to get a better grip on the situation. I hope this was clear. Let me know if we can be of further assistance. Thank you Matt, I need the formula to convert the. My way of thinking is it would be easier to know zone, angle wise verses Decimal wise. That tolerance zone is inclined by your basic angle relative to your datum A.

No matter how far off from true position you are. As long as the axis of your manufactured feature is entirely within this zone the part is good. I think you are asking how much variation in angle is allowed via this diameter tolerance zone. If this is indeed the case, some straightforward geometry should do the trick. The variation angle depends on the size of the tolerance zone and the wall thickness of the part.

A thicker wall is going to restrict your variation in the same manner a tighter tolerance zone would. Check my math here as I did this on a napkin. For a tolerance zone of d, at a basic angle of I assumed a wall thickness of. Yes, that is perfectly legal. We do it all the time. I have a customer part, where, their drawing calls out true position on the bore of a Round Single Bore Tube. The call out is. All examples I see are typically a cylindrical feature, hole or boss, on an otherwise linear planar part.

Anyone have advice or seen this kind of usage of true position before? The specific application that appears to be going on here is for positional tolerancing of coaxial features of opposed diameters. Datum A is the flat face of the part, this is the start of the universe for this part. From there the outer diameter, datum B, is constructed. Now, with datum A defined and datum B defined relative to datum A we locate the inner diameter with a diametral tolerance of.

Why have datum A as the flat surface and why have it called out first? My guess is that the end of the tube mates up against some other feature at a higher level assembly and it is more important for the inner diameter to be perpendicular to this surface than it is to be located relative to the outer diameter.

Any number of applications for parts could fit this bill. Remember, datum selection is based upon functionality at assembly. What mates first, is there a sequence of assembly that matters etc. I think your asking how to go about calculating the actual position of a hole versus the drawing requirement? This formula should clear up any issues. This will produce a diametral positional tolerance that you can compare against the drawing requirement.

If your calculated tolerance is larger than the one specified you are not in spec! The bonus tolerance is equal to the the amount of departure from MMC of the considered feature. This gets added to the tolerance value stated in the feature control frame. It has a positional tolerance of. For the purpose of our example locate your X,Y Cartesian coordinate system at the bottom left corner of the plate. In a perfect world the axis of the hole would always be located at 1, 1.

In reality there are always sources of error that prevent this from happening. You get the part in house and use a digital coordinate measurement machine to determine the actual location of the hole as 1. Is the part good? How do you figure it out? Delta X and Delta Y represent the difference between the actual measured location and the basic location. The position requirement was. Thus, this part must be rejected. I highly recommend going through some of the other comments in the true position forum as there are some other really good examples I have put up there.

I am having a hard time with this. How can a square with a size of 0. To me the square box has a larger tolerance zone. Though I know that two parts will not fit together the same way, or at all. I can easily clear up your confusion. Take a piece of paper and draw a perfect square. Now, over the square draw the smallest circle you can such that the corners touch the edge of the circle. Label all sides of the square The area of the square is If I asked you to calculate the area of the circle how would you proceed?

Where r is the radius. The point at which the square intersects the circle i. Plugging this back into the circle area formula we get — 3.

This person gathered like minded individuals and started developing commonly accepted standards that eventually evolved into what we know as ASME Y I understand your explanation but have one question. If the true position without a diameter call out is 10….. To me this should be Ah, in this case you are referring to a feature of size other than a circular one.

In that case you are controlling the center plane of the toleranced FOS a tab or slot as determined by parallel surfaces of the FOS. The tolerance value represents the total distance between two parallel planes. Sorry about all that, my previous explanation was bit long winded. For further information refer to Section 7. Let us know if you need any more help. Machine shops or metrology houses will have a digital Coordinate Measurement Machine CMM that does all the work digitally.

There is a small spherical diameter ball or probe on the end of an articulating arm that is hooked up to a machine with special software. After locating datum surfaces the hole position can be compared against the datum structure and ultimately the drawing. A fixed functional gage. If a part has a high quantity manufacturing run it may make sense to use a fixed functional gage.

The hole size would have to be verified separately. The gage for say, a block with a hole in it, would be one that simulates the referenced datum structure in your case A at MMB and B at MMB with a pin at the virtual condition of the hole and located relative to the datum structure. If the block fits over the gage, then the position requirement is met. Through the use of a special set of calipers http: How is this done? The drawing calls out basic dimensions or should these are theoretically exact dimensions.

The formula for calculating the actual positional tolerance to compare against the requirement is: Delta X and Delta Y represent the differences between the manufactured distance from a datum and the basic theoretically exact dimension. This could be done with a regular set of calipers without the cylindrical tip shown, but your accuracy will suffer greatly.

An alternate way would be to specify the axle of one wheel as a datum and have the axle of the wheel that is intended to be co-linear with it controlled using runout.

As for using positional tolerance I would refer you to section 7. This section addresses the capability to control coaxial positional tolerances through the use of composite positional tolerances.

In particular, Figure 7. It shows coaxial holes, but the concept also applies for external features of size. If the hole position is controlled by just 2 datums A and B in this case at what cross section along the hole would you use for measuring to determine whether its within tolerance?

For example, if you had a crooked hole, if you measure on the surface its good, but on the bottom its off. With a 3 datum setup you can control this. Just wondering for a 2 datum setup how would work. All parts of the hole axis have to be within the tolerance zone defined by the feature control frame with respect to your datum reference frame. In the above example, if the hole position was just controlled with respect to only datum A and B would the tolerance zone still be a cylinder?

Wouldnt this be the same tolerance zone if the hole were controlled with respect to A, B, and C? Not sure what the difference would be between controlling hole position with 2 vs 3 datums. The sequence of the datum reference frame A-B-C or C-B-A etc is telling the inspection department in which order to set up the part on the inspection table.

To begin measurement the primary datum comes in contact with the datum feature simulator, followed by the secondary and finally the tertiary. There is no set rule as to what your datum sequence should be, it really depends on your part and your assembly and what you view as the most important.

Now, with that being said, for flat parts it is normal to see the surface perpendicular to the hole as datum A, with datum B as the longest edge surface for stability on the inspection table and datum C as the next longest edge surface. You have to be able to basically theoretically exactly locate your feature of size relative to your datum reference frame.

With this bit of information you should be able to infer that you would need at a minimum of 2 datums in this case B and C to properly locate the FOS. All of your tolerance for your FOS comes from the feature control frame. Or do I have to calculate the true positional tolerance formula in order to know what distance I can have against the Datums? Could you elaborate, please?

Hello — When you have a cylindrical tolerance zone as indicated by the diameter symbol that means that the tolerance zone is located exactly where the basic dimensions place it. The axis of the feature must remain within this zone but is otherwise free to move anywhere within it. We delve into a grey area. Simplistically, for a flat rectangular part in order to be fully constrained there needs to be 3 datums.

These datums are essentially telling you that from your datum reference frame the axis of the hole is located theoretically exactly basically from two edges and theoretically perpendicular basically to the primary datum. Obviously, this changes when you start dealing with cylindrical parts. Every dimension and callout must have a tolerance in order for the part to be produced.

The feature control frame is describing a cylinder in which the axis of the part can vary this produces your tolerance. It can be a tricky subject and the more you deal with it the more sense it will make. Let us know if you need any additional clarification.

I would be happy to understand if my reading is wrong. In this particular example the designer is specifying that the edges are of more critical importance than the back flat surface. Remember that the order of datums is specifying the order in which the part comes into contact with the inspection equipment. In this particular case it is specified that first one edge, then the other, followed by the flat surface are to touch the inspection equipment.

Hi, I was wondering if it is possible to apply a percentage tolerance to true position. To further complicate things there is also a bleed tolerance where the ink will bleed out from the printed image and this is typically constant regardless of feature size. You might look into that avenue. Your application of positional tolerance to an ink-jet image is a new and intriguing one for me though!

The only time you should come across the discussion of radial tolerance is in a tolerance stack, i. You will only ever find the diametral or spherical diametral symbol prior to the tolerance in the feature control frame when they are required. I want to ask whether the position tolerance on a feature of size can be more than the total size tolerance on that feature of size.

Is there any explanation? Absolutely, there is no restriction on the tolerance with regard to the position control. It is only with the form controls that are governed by Rule 1 MMC at perfect form that require that the tolerance be smaller than the size tolerance, i.

For form controls this is the case unless: I am working on a drawing 2d to 3d and on there are two values of lmc and mmc for holes for eg 2. All help is appreciated. Are these mmc and lmc values or are they something else? What you are seeing is just one of the ways to represent a tolerance. Every dimension must have a tolerance and the different ways allow the designer to convey intent. If I were to put the dimension of a hole down as 2. The designer is indicating that he wants a hole of diameter 2.

The same applies for unilateral tolerance i. The case that you illustrate is known as limit dimensions where the absolute limits of size are indicated. In this scenario the designer is indicating the limits he can live with but is expressing no preference for size. As a CAD drafter or machinist I would split the difference when producing the hole so as to reduce the chances of having a part rejected i.

If I had two plates with holes in an array, what control features would I use to ensure the plates are always aligned? After reading up on this a little it seems like a true position diameter tolerance with an MMC condition referencing the same datums A, B, and C you did in both examples would be the way to do it.

Am I correct in that thinking? Hello Patrick, You are absolutely on the right track — Great work! I wish I could go into more detail about it here in the comments, but I may add this lesson as a free video for the site in the near future, since it is such a common application of Position.

They do represent datums, but not always flat planes. What that datum structure in the feature control frame is telling you is the sequence in which the part must contact the inspection equipment.

It is saying that first the part must be in contact with datum A, then B and lastly C. Can datum A control spatial? Can Datum A control plane rotation? Can Datum A control X,Y? Can Datum A control Z? Ok now on to Datum B, what is left to control? Can Datum B control Spatial? Can Datum B control Planar rotation? Now to Datum C. I have seen countless Datum schemes and the feature types are mixtures of planes, cylinders, spheres, torus, etc… The inspector must follow the order listed. They are very different simply by the order of the letters.

Hi, would you be able to answer my question below? If I have a plate with datum A B C being the base and edges. There are 2 holes in the plate. I require hole 1 to have a true position of 20mm with a positional tolerance of 0. I also want hole 2 to be positioned 10mm from hole 1 within a positional tolerance of 0. If the actual position of hole 1 ended up being Could this be achieved by chaining the dimensions between hole 1 and hole 2 similarly to what you have shown in example 1, only referencing datum ABC?

Or would I need to make Hole 1 a separate datum D, and reference datum D in the positional tolerance of hole 2?

The best way to go about doing this would be to change your datum structure so that hole 1 is datum D and hole 2 is then referenced off of that. The formula you quote is for determining the diametral tolerance zone, you should not be dividing by 2. This way you can directly compare against the requirement stated in the field of the drawing.

Let us know if you have any other questions. I have hole position: Y Basic is symmetry. Without the diameter symbol, how would you Calc TP? I think you may be mixing a few concepts together. Dear Team, I want to control all around form of the part which is plastic and it is going to be chrome plated. How I can define my tolerancing scheme without datums. Just in a note or by giving some presentation. Recall that if no datums are called out a profile control is only controlling the form. We use a similar note all the time at my company.

Hello, We have a disagreement between a few of us on how to interpret the call out on a print. We have a round pin the will have a hole drilled through the OD which is datum A. There is a basic dimension from the face on one end of the pin which is datum B. Both dimensions have the diameter symbol in front of them.

Our issue starts as one inspector claims we are only allowed the. A few of us disagree and feel as long as the two dimensions jive, and say within a figured tolerance pe the formular for X and Y coordinates, then we have acceptable parts. Can you please clarify as I fear we have been scrapping good parts. For the AB position I would say that at any point along the hole axis it should not deviate from the basic by more than 0.

For the A position I would say that at any point along the hole axis it should not deviate from the A datum axis by more than 0. The diameter symbol in these cases of no datum C can seem to be applied wrong, but they are actually controlling perpendicularity and position, which is why I noted at any point along the hole axis. The diameter zone of 0. I get quite a few drawings from one Company in particular that have a hole position datumed off the face it is drilled through, there is no reference to directional tolerance, only the face that it is on.

If a is the face of the paper, how do you work out the positional on a face? If the position is on a pattern, the requirement is simply to the pattern itself not any other feature on the part, Otherwise it is simply a perpendicularity tolerance.

Surely then, if it is just a single hole a perpendicularity symbol should be used to indicate that a cylinder measurement is required. If the part is a thin piece like paper thats not possible so would the positional tolerance meaningless? The perpendicularity still would theoretically exist, but may not be functionally necessary. You would still have to position the hole though in space and that is where Position will be important.

I have japanese drawing, where a nut is welded over a pierced hole. The position tolerance has LD written above it. I guess it stands for Lower Deviation, and it is a modifier for Feature of size, but I do not know how does it affect the calculation of the tolerance field. If it affects… 2xM6 LD pos. Yes, I was reading incorrectly. Total allowable tolerance would be callout tolerance plus bonus tolerance. Basic dimensions, how are basic dimensions recorded on a inspection report?

Do you ignore them? Do you record actual valves? Do you just list the nominal? Do you list the True Position that they control? Both the length and width are designated separately, and both have the same DRF. Is there anything special I should consider with this symbol? Err… maybe more generally what should people keep in mind when a slot IS a datum and not referenced to one? Yes I know one is the box on the print and the other is the mating envelope that designates the Datums.

There are numerous free tutorial sites but most act like they are tutoring an engineer who should not need the tutoring any way.

I have a test this coming week for a quality control position I applied for. I especially like the symbols laid out so one can click on them and get a thorough explanation of the meaning and application of it. I have years of experience as a web designer and that pops out as brilliant to me. It has been years since I took courses in drafting and design and this site made for a good memory refresher.

Thank you so much! We enjoy working to continue keeping this content up to date and really appreciate that you are learning from it.

We want to make sure we help as many people as possible with this often over-complicated topic. Good luck on your interview!

The inspector reports that the characteristisc is. How should I interpret this. Is this reporeted disprepancy is the distance from the center? Thank you in advance for help. Reported position tolerance is always in diametric size. Im learning a lot from your site. As i gain knowledge the more question pops up on my head. Can you asnweer me please. I have a hole mmc positional tolerance of 4thou, to check it im using a checking fixture. Now as we know fixture has tolerance also since we can not do perfectly as 0, 0.

The part is located and fixed on datums on the fixture. How i would be able to decide for the location tolerance of my checking pin on the fixture? Hello Mark- your basic dimensions are the location of these checking pins. Remember measurement equipment is theoretically perfect, however, you would need to look up the applicable gauge tolerance. The standard ASME y Should the symbol of datum A triangle be changed to point downward? There is nothing in the standard that dictates which way the symbol the triangle should be pointing.

The intent is clear that the bottom surface represents datum A. Sometimes stuff just fits together better the other way. Hello, first of all thanks for your contribution! I was wondering if the reference system is defined by the datums or by the exact dimensions. For example, in a case where the datums A and B are not perpendicular, but the exact dimensions are so. What if the plate was trapezoidal and the datum A and B were not perpendicular. If I consider that plate with the datum A as it is horizontal and the datum B with an angle with its own exact dimension.

I could still put the two exact dimensions 30 and 20, plus the angle. Thanks for your answer. As an example you could have a typical parallelogram with the flat face as your primary datum and your two edges as secondary and tertiary datums.

It does nothing to change how the concept of basic dimensions or tolerance zones work. In this case, however, you would need to dimension everything directly back to the vertex i. The way to handle this on a drawing typically is to use a basic angle and a basic dimension to your feature.

Step one when reviewing or creating a drawing is to locate your datum structure. All features using geometric tolerances that call out those datums must relate back to them. I have a question. Imagine a 50mm x 50mm square plate with four 5mm holes in a centred square pattern say 10mm from and edge and 30mm between centres in both directions. What is separate requirements? True Position Overview 7. Chapter 5 - Form Tolerances 8. Perpendicularity as a Refinement of Position 9.

Gauges, Dimensioning and Errors 7. When to use composite FCF? Geometric Dimensioning and Tolerancing Beginners- explained with example 7. Bonus Tolerance in Stack Up Analysis 7. Check out our course at http: This video talks about the 2 main benefits of using the Position symbol Simple explanation of how position tolerance is applied to assemblies.

Develop a passion for learning. If you do, you will never cease to grow. D'Angelo Purpose of this video is to discuss diffrent theories of interpretation while position tolerance On the last slide, the final diameter should be 50 Do Datums confuse you?

For more Tips visit http: Don Day starts a 3 part series on Composite Tolerancing. In this video I will discuss the basic rules of setting up a part using geometric dimension and tolerancing and to read a control frame. We discuss the definition of datums, the rules The only source of knowledge is experience. Albert Einstein Objective of this video is to discuss the different types of position tolerance. D'Angelo Purpose of this video session is to discuss advantages of circular tolerance zone over rectangular Try to learn something about everything and everything about something.

Thomas Huxley Objective of this session is to discuss concept of bonus tolerance in detail with case study and related

Ten

It just could have been done in a more conventional manner. Also, I understand why we give X, Y and Z dimensions for the axis location of tubes. But, giving X, Y and Z separate tolerances that are all the samenumber is odd.

Why not just give it a position control with a diameter of 4 millimeters that confines the axis of the tube. Here is an illustration from one of my textbooks: Datum Feature Shift Hello Mr. I am looking at a tool drawing someone designed with the second hole referenced to the first hole with a datum modifier MMB and a 3rdhole referenced to the 2nd hole at MMB.

I have attached a scan of a page from your book 1st and 2nd scanned pages. I understand the simplicity you used for the sake of explaining the concept, but otherwise, is there any practical reason to not set up the second hole to just have true position tolerance with extra bonus instead of a shift modifier?

Also, I have a question on the 3rd and 4th pages I scanned. So when there is a datum modifier, should I always consider the datum feature to shift with the type of tolerance in the original reference frame, like perpendicularity in the 3rdpage.

I have seen some explanations from others that made it seem as if you took your example, it would be looked at like a positional shift no matter if it originally referenced something like perpendicularity.

Best Regards, Joey The pages Joey scanned from one of my books: Granted, there are some isolated cases where this strategy might work out, but many more cases where it will not. Certainly, for a pattern of holes referenced to a datum regular feature of size such as one hole , as the datum regular feature of size departs from its virtual condition Maximum Material Boundary concept , that pattern of holes may shift as a group an additional amount.

This apparent shift of the pattern of holes is actually a movement of the datum feature axis away from its imaginary datum axis. This concept is thoroughly explained in other sections of this book. The planar primary datum will serve the purpose of perpendicularity control, while the secondary datum feature will be a hole which generates an axis that will be used to hold a millimeter distance.

So, datum A will be for perpendicularity and B will be for location in the following illustration. FIGURE [Part Drawing] In the simple example depicted below, the following illustrations show correct distributions of the tolerances that would allow parts to pass the gage. In reality, they are quite different. In Example 1, the shaft axis is controlled for perpendicularity within a diameter of 0.

As the shaft departs from MMC is made smaller, but still within size limits , the tolerance zone will grow to permit a maximum out-of-perpendicularity of the axis to datum plane A of a diameter of 0. Datum feature A has not, in this case, been controlled for flatness. Datum plane A is taken from the high points of the datum feature.

That surface must be within two parallel planes 0. All elements of the controlled feature bottom surface of the part must lie between these two parallel planes. This controlled feature is not only controlled for perpendicularity but also for flatness to within 0.

Since the surface being controlled by perpendicularity is not a feature of size, it is not allowed to be modified with the MMC symbol. The flatness of the surface is controlled to within 0.

This means that as the datum feature departs from its MMB is made smaller than The two parallel planes 0. This has the effect of increasing the allowed out-of-perpendicularity; but at the same time, the flatness of the controlled feature is held to within 0. When you have one hole positioned to another, it is like saying that they work together, for example, they mate with the same part.

If they mate with the same mating part, the MMB modifier used with the MMC modifier in the same control, is a way of saying that if either hole deviates from its virtual condition, the holes may deviate more from being perfectly positioned to each other. The larger the hole without being more out of perpendicularity to a planar primary datum , the more each hole may move away from the basic dimension that connects them. Picture a gage with two virtual condition sized gage pins on a plate, one for the datum feature referenced at MMB and the other for the hole being positioned.

As each hole grows without being made more out of perpendicularity to the primary planar datum , that hole may move more before it hits the gage pin. Or, as each hole grows, it may be more out of perpendicularity to the primary planar datum. Or, a little bit of both, but no more than the gage pins would allow. In that instance, the gage pin simulating the datum feature would have to expand into the hole, locking it up, and allowing no shift.

There is quite a bit of difference between angle and location. Position controls both angle and location, but perpendicularity controls only angle. So, the shift on a perpendicularity control that references a datum feature at MMB would only allow an angular shift zone, since the relationship being controlled is only one of angle not distance. I am still a little confused on the second concept I brought up and you explained, but this figure I attached actually illustrates my problem better than what I tried to use.

For the hole on the right, does the datum modifier of -B- at MMB represent added positional shift being in the original Datum Reference Frame of the feature datum or perpendicularity shift since that is what -B- has as a tolerance type of the feature datum? That one is positional shift. The relationship between the second hole being positioned and the first hole which is what the second hole is being positioned to is one of location.

So, as the first hole datum feature B grows from 49 toward 50, the second hole may shift away from the datum axis of B by the growth of B. Any out of perpendicularity of datum feature B negates the shift it allows as it grows. The theory, as explained in Y The theory is that as datum feature B grows, its axis may shift away from the imaginary datum axis B.

This is pretty easy to visualize, if you picture the gage I described with two pins on a plate. The first pin axis simulates datum axis B. If the hole B is larger than the gage pin virtual condition , the hole B axis may shift away from its own gage pin axis. So, to someone holding the part in their hands, it will appear as if the second hole has shifted away from its perfect location from the first hole. But, the theory is that it is the first hole that has shifted.

The axis of hole B datum feature B has shifted away from the imaginary datum axis B simulated by the axis of the gage pin. Runout and Free State. I hope you are doing well. I have taken a couple or your classes in Huntsville, AL, and I would like to get your input on a of couple questions, please. As I understand it 6. Figure p seems straight forward with respect to free state, however, Figure leaves me with some questions.

Thank you for your time,. Yes, the runout controls in Figure are free state measurements. All measurements are free state unless a note is written to specify they are to be restrained while measured. Free state measurements are considered those wherein the measurement equipment chucks, probes, etc.

In the gaging and fixturing standard Y Still, we all understand zero measurement force is unattainable. But the goal is understood to be: Yes, you can measure it on the same machine on which you manufacture the part. Taking the same example, the true position can also be specified with a maximum material condition callout. This means you are now controlling the envelope of the entire hole feature, including the size of the hole throughout its entire depth.

With an MMC callout you now can use a functional gauge to measure this part, to determine that the size and geometric tolerancing are within spec at the same time.

Formula for a the functional gauge to measure the true position of all holes: This would be the go gauge that would measure for hole size, orientation and position. The part would be pressed down onto the gauge and if it fits the part is in specification. Notice that datum A, B and C are all included in the gauge to check the location of the hole.

As long as the gauge can go into the part, it is in spec. This makes it very easy to accurately gauge the part right on a production line. The function of the part is confirmed because as long as the surface that the part is bolted to has the same tolerances, it will always fit.

Remember the further you are from MMC when it is referenced in the feature control frame, the more bonus tolerance you are allowed. Keep in mind the opposite is true for a positive feature like a pin, where the smaller the pin means you have more bonus tolerance. There are two ways true position can be called out — either as a distance, in X and Y or most commonly as a diameter. When true position is called out as a distance, you are permitted to move from the tolerance in X or Y direction by the allowed tolerance.

However when done this way, the tolerance zone actually forms a square. This is usually undesirable since in the corners of the square are further from the center than the sides. Another common way true position can be called out is with slotted features. If you have a slot in your part that must always be located correctly, you can use true position to ensure that each of the planes that make up the slot are always located in the correct position.

Symmetry can also be used in this case — but only if the slots have a referenced datum plane that they are symmetrical about and measuring symmetry is very difficult! Clean, functional, and with good explainations! Thanks for a great resource! Glad to hear it. We are rolling out a training program for students in at universities soon.

Thanks for the kind words! Glad to be of help! Simultaneous requirements are a useful thing to learn, but does not come us as much as some of the other material, such as MMB and datum reference frames. Thanks for the suggestion though, its good to know what information people are looking for. When the center distance of two holes shown with Basic Dimension and Datum shown at the left side leader line. Does that mean,the center of the two holes to be considered as a datum? Yes, you are absolutely allowed to use a pattern of holes or other FOS as a datum.

The net result being that the datum is then a plane or planes located exactly between the two features. To have the datum at either side of the basic leader would be incorrect. I hope this helps, keep the questions coming. While using Position control for hole in a plate ,having X axis-basic dimension and Y axis basic dimension, diameter symbol will precede tolerance in Feature Control Frame FCF. Instead of a hole ,a square opening is available at the plate with X axis-basic dimension and Y axis basic dimension to the center of the square opening.

Could diameter symbol precede the tolerance in FCF? When tolerance of position is used to control either a tab or a slot such as the example you cite no diameter symbol is allowed to precede the tolerance in the feature control frame.

The diameter symbol is restricted to the use of controlling circular features. Glad we could help. I guess the algorithm the machine is woring with is not the true position we are looking at. Either way is acceptable. I have a slot that is Datum C but it is dimensioned like this: If you have a datum that is constraining the part but it is say on the face of the hole or pin instead of the sides, you are controlling the orientation perpendicularity in a addition to the location the two datums on the side of the feature.

I hope this helps! I think I see an error in the formula used to calculate true position. Ill get that fixed right away. Thanks for pointing this out! You could insert the part and slide it down datum B instead either by accident , or design. Yes — all gauging must have instructions or a method to use. This is just a basic overview to understand the concept of gauging for a very simple part.

The instructions would have to state that you pin the part to datum A, then B and slide it down to datum C. The datum order does matter, and we will be covering this in a future article. Thanks for the comment! Under true position — location of a feature there is a statement that: I think the formula needs to result in less than one half of the position tolerance for that part to be within specification.

In other words, you calculated a vector distance from true to actual center. The positonal tolerance being diametral is 2x the max radial vector distance. You are right — there should be a 2 in front of the radical symbol to make it diametric. The beauty of true position is the use of basic dimensions. You are specifying exactly where the perfect nominal feature should be then simply saying how far off of that perfect location your feature can go to be in spec.

You would not put true position on a dimensional tolerance, because you are already specifying your position with your dimensions. The benefit of true position is that you are giving a clear nominal point, and by using datums, showing how the part should be measured and controlled.

You also have the benefit with true position of having a circular tolerance zone, thus giving you a little more functional tolerance than with the square tolerance zone that exists with X and Y dimensions.

Check out our page on Max Material Condition. We talk about how gauges are developed around the virtual condition that arise from the bonus tolerances. It makes thing simple. When creating a true position for a hole back to another hole, you need two datums in order to do this, correct?

You can chain basic dimensions off each other as long as they can be referenced to an original datum at some point. If these holes are concentric or coaxial, you can actually call out one of the holes as a datum, and then give the true position of the one hole to the other as long as your datum hole is also controlled in some way.

Pls share and advice about Tru position without Symbol Diameter Tru position 4. Usually it is better to use profile for these cases, without seeing the print my guess is that your true position of the line or plane needs to be 4. True Position is the theoretically exact location of a feature of size as established by basic dimensions. The Position tolerance of a feature of size is specified relative to the True Position.

I realize that the metrology field has historically mis-used the term True Position to mean Position, but that is beginning to change. According to the ASME y I think it is merely semantics though as if someone referred to a true position, you would understand that it is the exact point, but the true position tolerance would be the tolerance zone or range.

If we are going by the ASME though, it appears to always refer to the tolerance as position and the specific location as the true position. Great comment that got me thinking about this! Not sure, the SL is new for me. I am not sure if it is S L which do counteract eachother.

The two used together though would be counter-intuitive so I am not sure. The information I am learning so far is invaluable. The last couple of weeks we are seeing more and more of these drawings Datums and Callouts presented to us. Our only measuring devices are Mitutoyu calipers.

Can this measuring device be used for this application? Should we be investing in a CCM machine to properly perform the tests?

Thank you so much for the kind words! For measuring certain types of call-outs you need special equipment. For instance, measuring the parallelism of a plate, only requires a granite slab and a dial gauge. However if you are measuring the profile of a car hood, you will probably need more sophisticated equipment. A CMM is the ultimate measuring tool. Calipers on the other hand are really only good for measuring distance.

You may be able to roughly measure some geometry, but not very accurately. We go through each symbol and talk about what type of equipment is typically used in the industry to measure for it. Check out our training page if you are interested in learning more. Thanks for the great question! You should be investing in CMM Machine. I am a programmer for CMM and it really helps in out inspection. In general, the position tolerance of the Hole 2 mm is applicable individually to A, B and C datum separately… Which mean the position tolerance of the Hole 2 mm can vary individual from each datum A , B and C separately??

Not really — the position of the hole is taken when you constrain the part along datum A, B and C, Then you would measure the location to determine the location. If I place a position tolerance on a bolt hole around a nozzle bore, and reference the i.

Yes your surface datum, combined with the position tolerance will act just as a perpendicularity tolerance. Your cylindrical tolerance zone will be directly perpendicular to the bottom surface, and your hole axis will need to fall within this cylinder.

I have a question; if I want to know true position of a circle wrt to only one DATUM A which is a also circle then, still the same formula valid? Yes it is the same formula when calculating from X,Y components to Position tolerance.

I usually see True Position explained with hole positions and such. But how about for 2 flat surfaces in different areas? For example Datum A and Surface2 are supposed to be co-planar within 0. But they do not touch, they are separated by other features. If they were not on the same plane, then it would be easier because I could smack a dimension on Surface2 with on leader to Datum A a zero dimension is awkward.

This is actually a secondary use of Profile. If you call both surfaces with Profile and no datum they need to be located and within the form tolerance between them. Psition cannot control surfaces, only features of size holes, spins, slots tabs You are looking to us Profile to do this which can control the size, location orientation and form of surface elements.

I have a part with several features and several datums. First, I thought there was an engineering mistake but I have seen several drawing like this recently so it must be me missing something. Think of the datums as the ways of securing this in a frame. You now have your part secured in all 6 degrees of freedom.

Now you would determine how your bolt hole orients itself in 3D space. It would have to be perpendicular to Datum A. And only Located to Datum B and C. When using a perpendicular datum, like A in this case, Position controls the perpendicularity. The B and C establish where the perpendicular hole should be located in space.

I hope this is what you are asking. I understand it is possible to have different call out back to different datum but other than that is it possible? If one is a refinement of the other it is possible. Example, You can have a 0. Then a tighter 0. This way you are saying that the second tolerance needs to be met within the first tolerance. It is called a composite control.

Can you please let me know what is the correlation between the size tolerance value and true position tolerance value for a feature of size? Whether the true position tolerance value must always be less than the size tolerance value of a feature of size?

If true then why so? There is no correlation and the two tolerances can be independent. It all comes down to what you require for function. If you are trying to alight two holes with tight tolerances, your true position tolerance must be somewhat tight. However if you are locating a hole where a hose or wire must go through. You may have a tight fitting tolerance but a fairly loose position tolerance.

The image for the formula comparing true position and actual position is confusing. The formula makes sense if the goal is to get the distance of the positions by getting square root of x and y coordinate differences.

The correct formula is 2 times the square root of the distances. Yes, that is precisely correct. Draw your Cartesian coordinate system, place a 2 x 2 square at 0,0. Now, draw a circle that circumscribes the square with a center located at 0,0. The circle should only contact the square at the 4 corners. Thus, half the diagonal of the square from 0,0 is equal to the radius of the circle. To get the diameter you multiply the Pythagorean theorem by 2.

Pardon me but drawing a square centered at 0,0 and the diagonal distance and circumscribe it with a circle is just muddying the waters. In far simpler words, the TP tolerance defines the diameter of a circle centered at 0,0.

The actual center of the feature must be within the circle. The distance from 0,0 to the actual feature center must be equal to or less than half of the given TP tolerance value.

I have a customer that requires true position of a diameter on an end of a shaft from datum A which is a different diameter on the other end of the shaft. The datum and the diameter feature are considered theoretical centerlines correct? And measured as such RFS? Should this requirement be shown best as a true position call out or concentricity or maybe runnout?

Position could be the correct way as it would ensure that the axis of the diameter feature is coaxial to the datum axis within the position tolerance diameter. Runout and Concentricity are more than just making a part coaxial. Runout would be controlling the coaxiality and the circularity of the diameter feature. Concentricity is also controlling coaxiality but it making sure that the form of the diameter is evenly distributed. Runout on the other hand would be useful if the diameter feature was rotating and making contact with another part.

Runout is called a combined control because it can control the position of the axis coaxiality but also control the form circularity. The only thing you might want to add is a definition of the floating datum system, there TED theoretically exact dimension is only indicated between two or more features without any reference to datum.

In this case you must not use datum letters in tolerance definition and none of the relative degrees of freedom between TED and rest of the part is locked. Yes that is true — Position does not require datums if you are trying to align a theoretically exact dimension on something like a coaxial shaft. Hello everyboby, I have a question. What is a tolerance zone when the true position is within diameter symbol? May be the form of tolerance zone is square?

In the ISO I have many cases in my everyday practice us metrology specialist. This cylinder is located at the basic dimension location. If you calculate the X,Y coordinates away from the True Position, you would get your limit, however it would be the radial distance away from the center. Since Position is measured as a diameter you need to multiply by two to get the equivalent Position tolerance.

Even though you are only 0. One side wall is Datum B and have a hole at 1. The true position call out is. Something like this would be fairly hard to measure without any computer based measuring.

For the Datum AB top the design intent allows for a functional gauge to be used since the MMC symbol is used This would mean you would Setup a fixture to secure the pin and go perfectly center at datum A, and then butt up against datum B. You would then take a gauge pin at this exact location centered to datum A and 1.

For the second position callout, you would secure datum A, but not B. You would then have a gauge pin secured exactly center.

This gauge pin would be at the hole size — 0. If you want to know more about functional gauging we cover this in our fundamentals course.

Learn more at https: But how to measure it without CMM? I have a PCD of 76mm dia for threaded hole M6 with position tolerance 0. How can i measure this without CMM. Threaded holes are a gray area for functional gauging. However to truly ensure that the pitch is located correctly requires the use of a more advanced setup.

Thing is about true position with two datums. But these datums are paraller to each other. Round part with a eccentric hole. The datums are the outer diameter and the eccentric hole. Mikko — Sure, send it along. Did it bounce back? I hate doing something on blind faith.

It helps when I understand why I am doing something. True position is the diametric zone that the axis of the part should like within. Since it is a diameter it is dual sided and the formula needs to divide by 2 to go from a radius to a diameter. I hope you are finding the website material helpful in your studying.

I have a copy of the ISO standard and it appears that when you have a positional tolerance without the dia symbol applied to a circular hole, you are able to control the tolerance in two directions that are orthogonal to one another.

The tolerance zone in the feature control frame is telling you that the extracted actual median line of the hole must be contained within two pairs of parallel planes positioned apart by a distance equal to the value of the tolerance in the direction specified and perpendicular to each other.

Both pairs of planes are oriented relative to the datum reference frame and symmetrically disposed about the theoretically exact position of the considered hole.

I hope this helps. Hello, and thank you for this awesome resource! Wondering if you can help me out on this: The company I work for, one of their core manufacturing processes is laser cutting and subsequent press-brake air bending a secondary process that can be ignored for the sake of this question.

The profile is a piece of cake, since it does not have to rely on predetermined datums. Welcome and excellent question! Recall that, unlike profile, position requires the use of datum s. Also, keep in mind that without a datum callout, profile only controls form.

Note 1 always calls out material, Note 2 always calls out finish etc. This document could then specify for certain types of features which datums to use with a position tolerance in the drawing title block.

This route seems much more fraught with complications and opportunities for mistakes, however. Thank you Matt, definitely some food for thought here! Problem is, our parts are not defined by basic dimensions, but rather the CAD file itself more specifically, a DXF that is generated from the 2D drawing. Our flat parts are complex enough that full dimensioning is not practical not to mention unnecessary , but I still want to convey a certain dimensional expectation, based on the CAD file, not basic dimensions.

It would have to control not only the surface profile of individual cutout features, but also their location. Bill — I think you are most of the way there. This drawing does not fully define the product. The model does not fully define the product.

All dimensions obtained from the model are to be considered basic. Define all datums used in feature control frames 2. Specify on the drawing controls for all critical features or those that mate with other parts 3. Callout controls for all threaded features studs, tapped holes, helicoils, nutplates etc. Things like chamfers, radii, non critical holes, diameters, skin thicknesses etc. The important point here is that there are no dimensions or tolerances called out in the model.

This may not be the optimal way to do it, but it seems to work for us. Grab the bull by the horns Bill, be the agent of change. Datum A is the OD of tube. How do I figure tolerance zone of Basic angle from a Dimensional callout? I am using an Optical Comparator to inspect.

Datum A as you have it defined for your part is the central axis of the tube. Your hole is located at a theoretically exact angle from this center line of Note that the theoretically exact centerline of your line intersects with datum A.

It is about this theoretically exact line that the diametral tolerance of. As for inspection with an optical comparator what comes to mind is to place a gage pin of appropriate diameter in the hole and then place them both in the comparator. If your drawing is dimensioned how I think it is with an angle and an off-set distance you should be able to verify this on the comparitor.

You would treat it the same as you would with orthogonal thru holes in a flat plate. This should at least give you a few ideas of which direction to head down. I hope this helps, let us know what you actually end up settling on. We want to keep the forums here healthy and active with useful information.

Yikes, delving into some more complicated material here. First, in the standard the terms Inner and Outer Boundaries are done away with. The symbols circle M and circle L , application and interpretation of the meaning remain the same between the and standards. What they allow for is: The use of fixed functional gages. Imagine a circular part.

Your datum feature simulator for datum A has a diameter of 9 MMB size. Your functional gage to verify location of the smaller holes would have pin diameters of 2. Your gage would look like the negative image of your part, i. Without the MMB callout, you would have to reject the part. With the MMB callout you are able to move the part in the gage to hopefully get your part to fit not always possible as the center hole of the part departs from MMB to LMB. However, if the part center hole is produced at 11 you have 1 of float in any one direction to get your part to fit.

You are in effect re-centering the axis of the part. Caution, if you have features opposed to one another that wander in opposite directions, no amount of float over the gage is going to get you into a fit condition.

It does get a little bit more complicated than this as you must respect controls of higher precedence datums. However, this should allow to get a better grip on the situation. I hope this was clear. Let me know if we can be of further assistance.

Thank you Matt, I need the formula to convert the. My way of thinking is it would be easier to know zone, angle wise verses Decimal wise. That tolerance zone is inclined by your basic angle relative to your datum A.

No matter how far off from true position you are. As long as the axis of your manufactured feature is entirely within this zone the part is good. I think you are asking how much variation in angle is allowed via this diameter tolerance zone.

If this is indeed the case, some straightforward geometry should do the trick. The variation angle depends on the size of the tolerance zone and the wall thickness of the part. A thicker wall is going to restrict your variation in the same manner a tighter tolerance zone would.

Check my math here as I did this on a napkin. For a tolerance zone of d, at a basic angle of I assumed a wall thickness of.

Yes, that is perfectly legal. We do it all the time. I have a customer part, where, their drawing calls out true position on the bore of a Round Single Bore Tube. The call out is. All examples I see are typically a cylindrical feature, hole or boss, on an otherwise linear planar part. Anyone have advice or seen this kind of usage of true position before? The specific application that appears to be going on here is for positional tolerancing of coaxial features of opposed diameters. Datum A is the flat face of the part, this is the start of the universe for this part.

From there the outer diameter, datum B, is constructed. Now, with datum A defined and datum B defined relative to datum A we locate the inner diameter with a diametral tolerance of.

Why have datum A as the flat surface and why have it called out first? My guess is that the end of the tube mates up against some other feature at a higher level assembly and it is more important for the inner diameter to be perpendicular to this surface than it is to be located relative to the outer diameter.

Any number of applications for parts could fit this bill. Remember, datum selection is based upon functionality at assembly. What mates first, is there a sequence of assembly that matters etc. I think your asking how to go about calculating the actual position of a hole versus the drawing requirement? This formula should clear up any issues. This will produce a diametral positional tolerance that you can compare against the drawing requirement. If your calculated tolerance is larger than the one specified you are not in spec!

The bonus tolerance is equal to the the amount of departure from MMC of the considered feature. This gets added to the tolerance value stated in the feature control frame. It has a positional tolerance of. For the purpose of our example locate your X,Y Cartesian coordinate system at the bottom left corner of the plate.

In a perfect world the axis of the hole would always be located at 1, 1. In reality there are always sources of error that prevent this from happening. You get the part in house and use a digital coordinate measurement machine to determine the actual location of the hole as 1. Is the part good? How do you figure it out?

Delta X and Delta Y represent the difference between the actual measured location and the basic location. The position requirement was. Thus, this part must be rejected. I highly recommend going through some of the other comments in the true position forum as there are some other really good examples I have put up there. I am having a hard time with this. How can a square with a size of 0.

To me the square box has a larger tolerance zone. Though I know that two parts will not fit together the same way, or at all. I can easily clear up your confusion. Take a piece of paper and draw a perfect square. Now, over the square draw the smallest circle you can such that the corners touch the edge of the circle.

Label all sides of the square The area of the square is If I asked you to calculate the area of the circle how would you proceed? Where r is the radius. The point at which the square intersects the circle i.

Plugging this back into the circle area formula we get — 3. This person gathered like minded individuals and started developing commonly accepted standards that eventually evolved into what we know as ASME Y I understand your explanation but have one question.

If the true position without a diameter call out is 10….. To me this should be Ah, in this case you are referring to a feature of size other than a circular one. In that case you are controlling the center plane of the toleranced FOS a tab or slot as determined by parallel surfaces of the FOS. The tolerance value represents the total distance between two parallel planes. Sorry about all that, my previous explanation was bit long winded.

For further information refer to Section 7. Let us know if you need any more help. Machine shops or metrology houses will have a digital Coordinate Measurement Machine CMM that does all the work digitally.

There is a small spherical diameter ball or probe on the end of an articulating arm that is hooked up to a machine with special software.

After locating datum surfaces the hole position can be compared against the datum structure and ultimately the drawing. A fixed functional gage. If a part has a high quantity manufacturing run it may make sense to use a fixed functional gage.

The hole size would have to be verified separately. The gage for say, a block with a hole in it, would be one that simulates the referenced datum structure in your case A at MMB and B at MMB with a pin at the virtual condition of the hole and located relative to the datum structure.

If the block fits over the gage, then the position requirement is met. Through the use of a special set of calipers http: How is this done? The drawing calls out basic dimensions or should these are theoretically exact dimensions. The formula for calculating the actual positional tolerance to compare against the requirement is: Delta X and Delta Y represent the differences between the manufactured distance from a datum and the basic theoretically exact dimension.

This could be done with a regular set of calipers without the cylindrical tip shown, but your accuracy will suffer greatly. An alternate way would be to specify the axle of one wheel as a datum and have the axle of the wheel that is intended to be co-linear with it controlled using runout.

As for using positional tolerance I would refer you to section 7. This section addresses the capability to control coaxial positional tolerances through the use of composite positional tolerances. In particular, Figure 7. It shows coaxial holes, but the concept also applies for external features of size.

If the hole position is controlled by just 2 datums A and B in this case at what cross section along the hole would you use for measuring to determine whether its within tolerance?

For example, if you had a crooked hole, if you measure on the surface its good, but on the bottom its off. With a 3 datum setup you can control this. Just wondering for a 2 datum setup how would work.

All parts of the hole axis have to be within the tolerance zone defined by the feature control frame with respect to your datum reference frame. In the above example, if the hole position was just controlled with respect to only datum A and B would the tolerance zone still be a cylinder? Wouldnt this be the same tolerance zone if the hole were controlled with respect to A, B, and C? Not sure what the difference would be between controlling hole position with 2 vs 3 datums.

The sequence of the datum reference frame A-B-C or C-B-A etc is telling the inspection department in which order to set up the part on the inspection table. To begin measurement the primary datum comes in contact with the datum feature simulator, followed by the secondary and finally the tertiary.

There is no set rule as to what your datum sequence should be, it really depends on your part and your assembly and what you view as the most important. Now, with that being said, for flat parts it is normal to see the surface perpendicular to the hole as datum A, with datum B as the longest edge surface for stability on the inspection table and datum C as the next longest edge surface.

You have to be able to basically theoretically exactly locate your feature of size relative to your datum reference frame. With this bit of information you should be able to infer that you would need at a minimum of 2 datums in this case B and C to properly locate the FOS. All of your tolerance for your FOS comes from the feature control frame. Or do I have to calculate the true positional tolerance formula in order to know what distance I can have against the Datums?

Could you elaborate, please? Hello — When you have a cylindrical tolerance zone as indicated by the diameter symbol that means that the tolerance zone is located exactly where the basic dimensions place it. The axis of the feature must remain within this zone but is otherwise free to move anywhere within it. We delve into a grey area. Simplistically, for a flat rectangular part in order to be fully constrained there needs to be 3 datums. These datums are essentially telling you that from your datum reference frame the axis of the hole is located theoretically exactly basically from two edges and theoretically perpendicular basically to the primary datum.

Obviously, this changes when you start dealing with cylindrical parts. Every dimension and callout must have a tolerance in order for the part to be produced. The feature control frame is describing a cylinder in which the axis of the part can vary this produces your tolerance.

It can be a tricky subject and the more you deal with it the more sense it will make. Let us know if you need any additional clarification. I would be happy to understand if my reading is wrong. In this particular example the designer is specifying that the edges are of more critical importance than the back flat surface. Remember that the order of datums is specifying the order in which the part comes into contact with the inspection equipment. In this particular case it is specified that first one edge, then the other, followed by the flat surface are to touch the inspection equipment.

Hi, I was wondering if it is possible to apply a percentage tolerance to true position. To further complicate things there is also a bleed tolerance where the ink will bleed out from the printed image and this is typically constant regardless of feature size.

the sport

When to use composite FCF? Geometric Dimensioning and Tolerancing Beginners- explained with example 7. Bonus Tolerance in Stack Up Analysis 7. Check out our course at http: This video talks about the 2 main benefits of using the Position symbol Simple explanation of how position tolerance is applied to assemblies.

Develop a passion for learning. If you do, you will never cease to grow. D'Angelo Purpose of this video is to discuss diffrent theories of interpretation while position tolerance On the last slide, the final diameter should be 50 Do Datums confuse you? For more Tips visit http: Don Day starts a 3 part series on Composite Tolerancing. In this video I will discuss the basic rules of setting up a part using geometric dimension and tolerancing and to read a control frame.

We discuss the definition of datums, the rules The only source of knowledge is experience. Albert Einstein Objective of this video is to discuss the different types of position tolerance. D'Angelo Purpose of this video session is to discuss advantages of circular tolerance zone over rectangular Try to learn something about everything and everything about something. Thomas Huxley Objective of this session is to discuss concept of bonus tolerance in detail with case study and related Don Day continues his 3 part series on Composite Tolerancing.

For more Tips go to http: Section 7 - Tolerances Add positional tolerance annotations to your drawing 7 By Pandora Beck. Virtual Condition - Holes and Pins Summary: This route seems much more fraught with complications and opportunities for mistakes, however.

Thank you Matt, definitely some food for thought here! Problem is, our parts are not defined by basic dimensions, but rather the CAD file itself more specifically, a DXF that is generated from the 2D drawing.

Our flat parts are complex enough that full dimensioning is not practical not to mention unnecessary , but I still want to convey a certain dimensional expectation, based on the CAD file, not basic dimensions. It would have to control not only the surface profile of individual cutout features, but also their location.

Bill — I think you are most of the way there. This drawing does not fully define the product. The model does not fully define the product. All dimensions obtained from the model are to be considered basic. Define all datums used in feature control frames 2.

Specify on the drawing controls for all critical features or those that mate with other parts 3. Callout controls for all threaded features studs, tapped holes, helicoils, nutplates etc. Things like chamfers, radii, non critical holes, diameters, skin thicknesses etc.

The important point here is that there are no dimensions or tolerances called out in the model. This may not be the optimal way to do it, but it seems to work for us. Grab the bull by the horns Bill, be the agent of change. Datum A is the OD of tube. How do I figure tolerance zone of Basic angle from a Dimensional callout? I am using an Optical Comparator to inspect.

Datum A as you have it defined for your part is the central axis of the tube. Your hole is located at a theoretically exact angle from this center line of Note that the theoretically exact centerline of your line intersects with datum A.

It is about this theoretically exact line that the diametral tolerance of. As for inspection with an optical comparator what comes to mind is to place a gage pin of appropriate diameter in the hole and then place them both in the comparator. If your drawing is dimensioned how I think it is with an angle and an off-set distance you should be able to verify this on the comparitor. You would treat it the same as you would with orthogonal thru holes in a flat plate.

This should at least give you a few ideas of which direction to head down. I hope this helps, let us know what you actually end up settling on. We want to keep the forums here healthy and active with useful information. Yikes, delving into some more complicated material here. First, in the standard the terms Inner and Outer Boundaries are done away with.

The symbols circle M and circle L , application and interpretation of the meaning remain the same between the and standards.

What they allow for is: The use of fixed functional gages. Imagine a circular part. Your datum feature simulator for datum A has a diameter of 9 MMB size. Your functional gage to verify location of the smaller holes would have pin diameters of 2. Your gage would look like the negative image of your part, i. Without the MMB callout, you would have to reject the part. With the MMB callout you are able to move the part in the gage to hopefully get your part to fit not always possible as the center hole of the part departs from MMB to LMB.

However, if the part center hole is produced at 11 you have 1 of float in any one direction to get your part to fit. You are in effect re-centering the axis of the part. Caution, if you have features opposed to one another that wander in opposite directions, no amount of float over the gage is going to get you into a fit condition.

It does get a little bit more complicated than this as you must respect controls of higher precedence datums. However, this should allow to get a better grip on the situation. I hope this was clear. Let me know if we can be of further assistance.

Thank you Matt, I need the formula to convert the. My way of thinking is it would be easier to know zone, angle wise verses Decimal wise. That tolerance zone is inclined by your basic angle relative to your datum A. No matter how far off from true position you are. As long as the axis of your manufactured feature is entirely within this zone the part is good.

I think you are asking how much variation in angle is allowed via this diameter tolerance zone. If this is indeed the case, some straightforward geometry should do the trick. The variation angle depends on the size of the tolerance zone and the wall thickness of the part. A thicker wall is going to restrict your variation in the same manner a tighter tolerance zone would.

Check my math here as I did this on a napkin. For a tolerance zone of d, at a basic angle of I assumed a wall thickness of. Yes, that is perfectly legal. We do it all the time. I have a customer part, where, their drawing calls out true position on the bore of a Round Single Bore Tube.

The call out is. All examples I see are typically a cylindrical feature, hole or boss, on an otherwise linear planar part. Anyone have advice or seen this kind of usage of true position before? The specific application that appears to be going on here is for positional tolerancing of coaxial features of opposed diameters.

Datum A is the flat face of the part, this is the start of the universe for this part. From there the outer diameter, datum B, is constructed. Now, with datum A defined and datum B defined relative to datum A we locate the inner diameter with a diametral tolerance of. Why have datum A as the flat surface and why have it called out first? My guess is that the end of the tube mates up against some other feature at a higher level assembly and it is more important for the inner diameter to be perpendicular to this surface than it is to be located relative to the outer diameter.

Any number of applications for parts could fit this bill. Remember, datum selection is based upon functionality at assembly. What mates first, is there a sequence of assembly that matters etc. I think your asking how to go about calculating the actual position of a hole versus the drawing requirement?

This formula should clear up any issues. This will produce a diametral positional tolerance that you can compare against the drawing requirement.

If your calculated tolerance is larger than the one specified you are not in spec! The bonus tolerance is equal to the the amount of departure from MMC of the considered feature. This gets added to the tolerance value stated in the feature control frame. It has a positional tolerance of. For the purpose of our example locate your X,Y Cartesian coordinate system at the bottom left corner of the plate. In a perfect world the axis of the hole would always be located at 1, 1.

In reality there are always sources of error that prevent this from happening. You get the part in house and use a digital coordinate measurement machine to determine the actual location of the hole as 1.

Is the part good? How do you figure it out? Delta X and Delta Y represent the difference between the actual measured location and the basic location. The position requirement was.

Thus, this part must be rejected. I highly recommend going through some of the other comments in the true position forum as there are some other really good examples I have put up there.

I am having a hard time with this. How can a square with a size of 0. To me the square box has a larger tolerance zone. Though I know that two parts will not fit together the same way, or at all. I can easily clear up your confusion. Take a piece of paper and draw a perfect square. Now, over the square draw the smallest circle you can such that the corners touch the edge of the circle.

Label all sides of the square The area of the square is If I asked you to calculate the area of the circle how would you proceed? Where r is the radius. The point at which the square intersects the circle i. Plugging this back into the circle area formula we get — 3. This person gathered like minded individuals and started developing commonly accepted standards that eventually evolved into what we know as ASME Y I understand your explanation but have one question.

If the true position without a diameter call out is 10….. To me this should be Ah, in this case you are referring to a feature of size other than a circular one. In that case you are controlling the center plane of the toleranced FOS a tab or slot as determined by parallel surfaces of the FOS. The tolerance value represents the total distance between two parallel planes. Sorry about all that, my previous explanation was bit long winded. For further information refer to Section 7.

Let us know if you need any more help. Machine shops or metrology houses will have a digital Coordinate Measurement Machine CMM that does all the work digitally.

There is a small spherical diameter ball or probe on the end of an articulating arm that is hooked up to a machine with special software.

After locating datum surfaces the hole position can be compared against the datum structure and ultimately the drawing. A fixed functional gage. If a part has a high quantity manufacturing run it may make sense to use a fixed functional gage. The hole size would have to be verified separately. The gage for say, a block with a hole in it, would be one that simulates the referenced datum structure in your case A at MMB and B at MMB with a pin at the virtual condition of the hole and located relative to the datum structure.

If the block fits over the gage, then the position requirement is met. Through the use of a special set of calipers http: How is this done? The drawing calls out basic dimensions or should these are theoretically exact dimensions. The formula for calculating the actual positional tolerance to compare against the requirement is: Delta X and Delta Y represent the differences between the manufactured distance from a datum and the basic theoretically exact dimension.

This could be done with a regular set of calipers without the cylindrical tip shown, but your accuracy will suffer greatly.

An alternate way would be to specify the axle of one wheel as a datum and have the axle of the wheel that is intended to be co-linear with it controlled using runout. As for using positional tolerance I would refer you to section 7. This section addresses the capability to control coaxial positional tolerances through the use of composite positional tolerances.

In particular, Figure 7. It shows coaxial holes, but the concept also applies for external features of size. If the hole position is controlled by just 2 datums A and B in this case at what cross section along the hole would you use for measuring to determine whether its within tolerance?

For example, if you had a crooked hole, if you measure on the surface its good, but on the bottom its off. With a 3 datum setup you can control this. Just wondering for a 2 datum setup how would work. All parts of the hole axis have to be within the tolerance zone defined by the feature control frame with respect to your datum reference frame.

In the above example, if the hole position was just controlled with respect to only datum A and B would the tolerance zone still be a cylinder? Wouldnt this be the same tolerance zone if the hole were controlled with respect to A, B, and C? Not sure what the difference would be between controlling hole position with 2 vs 3 datums. The sequence of the datum reference frame A-B-C or C-B-A etc is telling the inspection department in which order to set up the part on the inspection table.

To begin measurement the primary datum comes in contact with the datum feature simulator, followed by the secondary and finally the tertiary. There is no set rule as to what your datum sequence should be, it really depends on your part and your assembly and what you view as the most important. Now, with that being said, for flat parts it is normal to see the surface perpendicular to the hole as datum A, with datum B as the longest edge surface for stability on the inspection table and datum C as the next longest edge surface.

You have to be able to basically theoretically exactly locate your feature of size relative to your datum reference frame. With this bit of information you should be able to infer that you would need at a minimum of 2 datums in this case B and C to properly locate the FOS. All of your tolerance for your FOS comes from the feature control frame. Or do I have to calculate the true positional tolerance formula in order to know what distance I can have against the Datums?

Could you elaborate, please? Hello — When you have a cylindrical tolerance zone as indicated by the diameter symbol that means that the tolerance zone is located exactly where the basic dimensions place it. The axis of the feature must remain within this zone but is otherwise free to move anywhere within it. We delve into a grey area. Simplistically, for a flat rectangular part in order to be fully constrained there needs to be 3 datums.

These datums are essentially telling you that from your datum reference frame the axis of the hole is located theoretically exactly basically from two edges and theoretically perpendicular basically to the primary datum. Obviously, this changes when you start dealing with cylindrical parts. Every dimension and callout must have a tolerance in order for the part to be produced. The feature control frame is describing a cylinder in which the axis of the part can vary this produces your tolerance.

It can be a tricky subject and the more you deal with it the more sense it will make. Let us know if you need any additional clarification.

I would be happy to understand if my reading is wrong. In this particular example the designer is specifying that the edges are of more critical importance than the back flat surface. Remember that the order of datums is specifying the order in which the part comes into contact with the inspection equipment. In this particular case it is specified that first one edge, then the other, followed by the flat surface are to touch the inspection equipment.

Hi, I was wondering if it is possible to apply a percentage tolerance to true position. To further complicate things there is also a bleed tolerance where the ink will bleed out from the printed image and this is typically constant regardless of feature size. You might look into that avenue. Your application of positional tolerance to an ink-jet image is a new and intriguing one for me though!

The only time you should come across the discussion of radial tolerance is in a tolerance stack, i. You will only ever find the diametral or spherical diametral symbol prior to the tolerance in the feature control frame when they are required.

I want to ask whether the position tolerance on a feature of size can be more than the total size tolerance on that feature of size.

Is there any explanation? Absolutely, there is no restriction on the tolerance with regard to the position control. It is only with the form controls that are governed by Rule 1 MMC at perfect form that require that the tolerance be smaller than the size tolerance, i. For form controls this is the case unless: I am working on a drawing 2d to 3d and on there are two values of lmc and mmc for holes for eg 2. All help is appreciated.

Are these mmc and lmc values or are they something else? What you are seeing is just one of the ways to represent a tolerance. Every dimension must have a tolerance and the different ways allow the designer to convey intent. If I were to put the dimension of a hole down as 2. The designer is indicating that he wants a hole of diameter 2. The same applies for unilateral tolerance i. The case that you illustrate is known as limit dimensions where the absolute limits of size are indicated.

In this scenario the designer is indicating the limits he can live with but is expressing no preference for size. As a CAD drafter or machinist I would split the difference when producing the hole so as to reduce the chances of having a part rejected i.

If I had two plates with holes in an array, what control features would I use to ensure the plates are always aligned? After reading up on this a little it seems like a true position diameter tolerance with an MMC condition referencing the same datums A, B, and C you did in both examples would be the way to do it.

Am I correct in that thinking? Hello Patrick, You are absolutely on the right track — Great work! I wish I could go into more detail about it here in the comments, but I may add this lesson as a free video for the site in the near future, since it is such a common application of Position.

They do represent datums, but not always flat planes. What that datum structure in the feature control frame is telling you is the sequence in which the part must contact the inspection equipment. It is saying that first the part must be in contact with datum A, then B and lastly C. Can datum A control spatial?

Can Datum A control plane rotation? Can Datum A control X,Y? Can Datum A control Z? Ok now on to Datum B, what is left to control? Can Datum B control Spatial? Can Datum B control Planar rotation? Now to Datum C. I have seen countless Datum schemes and the feature types are mixtures of planes, cylinders, spheres, torus, etc… The inspector must follow the order listed.

They are very different simply by the order of the letters. Hi, would you be able to answer my question below? If I have a plate with datum A B C being the base and edges. There are 2 holes in the plate. I require hole 1 to have a true position of 20mm with a positional tolerance of 0. I also want hole 2 to be positioned 10mm from hole 1 within a positional tolerance of 0. If the actual position of hole 1 ended up being Could this be achieved by chaining the dimensions between hole 1 and hole 2 similarly to what you have shown in example 1, only referencing datum ABC?

Or would I need to make Hole 1 a separate datum D, and reference datum D in the positional tolerance of hole 2? The best way to go about doing this would be to change your datum structure so that hole 1 is datum D and hole 2 is then referenced off of that. The formula you quote is for determining the diametral tolerance zone, you should not be dividing by 2.

This way you can directly compare against the requirement stated in the field of the drawing. Let us know if you have any other questions. I have hole position: Y Basic is symmetry.

Without the diameter symbol, how would you Calc TP? I think you may be mixing a few concepts together. Dear Team, I want to control all around form of the part which is plastic and it is going to be chrome plated.

How I can define my tolerancing scheme without datums. Just in a note or by giving some presentation. Recall that if no datums are called out a profile control is only controlling the form. We use a similar note all the time at my company. Hello, We have a disagreement between a few of us on how to interpret the call out on a print. We have a round pin the will have a hole drilled through the OD which is datum A. There is a basic dimension from the face on one end of the pin which is datum B.

Both dimensions have the diameter symbol in front of them. Our issue starts as one inspector claims we are only allowed the. A few of us disagree and feel as long as the two dimensions jive, and say within a figured tolerance pe the formular for X and Y coordinates, then we have acceptable parts.

Can you please clarify as I fear we have been scrapping good parts. For the AB position I would say that at any point along the hole axis it should not deviate from the basic by more than 0. For the A position I would say that at any point along the hole axis it should not deviate from the A datum axis by more than 0. The diameter symbol in these cases of no datum C can seem to be applied wrong, but they are actually controlling perpendicularity and position, which is why I noted at any point along the hole axis.

The diameter zone of 0. I get quite a few drawings from one Company in particular that have a hole position datumed off the face it is drilled through, there is no reference to directional tolerance, only the face that it is on. If a is the face of the paper, how do you work out the positional on a face? If the position is on a pattern, the requirement is simply to the pattern itself not any other feature on the part, Otherwise it is simply a perpendicularity tolerance.

Surely then, if it is just a single hole a perpendicularity symbol should be used to indicate that a cylinder measurement is required. If the part is a thin piece like paper thats not possible so would the positional tolerance meaningless? The perpendicularity still would theoretically exist, but may not be functionally necessary. You would still have to position the hole though in space and that is where Position will be important.

I have japanese drawing, where a nut is welded over a pierced hole. The position tolerance has LD written above it. I guess it stands for Lower Deviation, and it is a modifier for Feature of size, but I do not know how does it affect the calculation of the tolerance field.

If it affects… 2xM6 LD pos. Yes, I was reading incorrectly. Total allowable tolerance would be callout tolerance plus bonus tolerance. Basic dimensions, how are basic dimensions recorded on a inspection report? Do you ignore them? Do you record actual valves? Do you just list the nominal? Do you list the True Position that they control? Both the length and width are designated separately, and both have the same DRF.

Is there anything special I should consider with this symbol? Err… maybe more generally what should people keep in mind when a slot IS a datum and not referenced to one? Yes I know one is the box on the print and the other is the mating envelope that designates the Datums. There are numerous free tutorial sites but most act like they are tutoring an engineer who should not need the tutoring any way. I have a test this coming week for a quality control position I applied for.

I especially like the symbols laid out so one can click on them and get a thorough explanation of the meaning and application of it. I have years of experience as a web designer and that pops out as brilliant to me. It has been years since I took courses in drafting and design and this site made for a good memory refresher.

Thank you so much! We enjoy working to continue keeping this content up to date and really appreciate that you are learning from it. We want to make sure we help as many people as possible with this often over-complicated topic. Good luck on your interview! The inspector reports that the characteristisc is. How should I interpret this. Is this reporeted disprepancy is the distance from the center? Thank you in advance for help. Reported position tolerance is always in diametric size.

Im learning a lot from your site. As i gain knowledge the more question pops up on my head. Can you asnweer me please.

I have a hole mmc positional tolerance of 4thou, to check it im using a checking fixture. Now as we know fixture has tolerance also since we can not do perfectly as 0, 0.

The part is located and fixed on datums on the fixture. How i would be able to decide for the location tolerance of my checking pin on the fixture?

Hello Mark- your basic dimensions are the location of these checking pins. Remember measurement equipment is theoretically perfect, however, you would need to look up the applicable gauge tolerance. The standard ASME y Should the symbol of datum A triangle be changed to point downward? There is nothing in the standard that dictates which way the symbol the triangle should be pointing.

The intent is clear that the bottom surface represents datum A. Sometimes stuff just fits together better the other way. Hello, first of all thanks for your contribution! I was wondering if the reference system is defined by the datums or by the exact dimensions. For example, in a case where the datums A and B are not perpendicular, but the exact dimensions are so. What if the plate was trapezoidal and the datum A and B were not perpendicular.

If I consider that plate with the datum A as it is horizontal and the datum B with an angle with its own exact dimension. I could still put the two exact dimensions 30 and 20, plus the angle. Thanks for your answer. As an example you could have a typical parallelogram with the flat face as your primary datum and your two edges as secondary and tertiary datums.

It does nothing to change how the concept of basic dimensions or tolerance zones work. In this case, however, you would need to dimension everything directly back to the vertex i. The way to handle this on a drawing typically is to use a basic angle and a basic dimension to your feature. Step one when reviewing or creating a drawing is to locate your datum structure. All features using geometric tolerances that call out those datums must relate back to them. I have a question. Imagine a 50mm x 50mm square plate with four 5mm holes in a centred square pattern say 10mm from and edge and 30mm between centres in both directions.

Now consider the tolerances. I want the holes to be in true position in relation to one another within 0. The position of the holes with respect to the edges of the plate are of little importance to me, say the entire hole pattern could be located with tolerances of 2mm with respect to the edges of the plate. I am not sure how to specify this tolerance on the holes in a drawing, particularly the internal relationship between the holes.

True position requires a reference. What reference do I choose? You are describing a classic example of a composite positional control. For a composite control you have two segments feature control frames one directly above the other , only the position symbol is entered once and the height of both feature control frames. The tolerance for the upper control frame can be large, as you suggest 2 mm, keep your datum structure as A, B, C. Then for the lower segment enter 0. It can get a little more complicated depending on whether you want the pattern oriented a particular way, or basically located from one of the datums.

Otherwise you are good to go. True Position —Location of a Feature Position in terms of the axis, point or plane defines how much variation a feature can have from a specified exact true location.

True Position —Location of a feature A 2 dimensional cylindrical zone or, more commonly a 3-Dimensional cylinder, centered at the true position location referenced by the datums. True Position —Location of a Feature True position of a feature is made by first determining the current referenced point and then comparing that to any datum surfaces to determine how far off this true center the feature is.

Note on Bonus Tolerance: True Position —Location of a feature True position is closely related to symmetry and concentricity as they both require the location of features to be controlled.

True Position —Location of a feature In example 1 you can see how a hole can be called out using true position. True Position —Location of Hole Example 1: The True position callout on a block With true position called out the holes do not need to be in exact positions as shown below, but their centers can vary by the amount specified by the tolerance.

Same specifications This would be the go gauge that would measure for hole size, orientation and position. Top view of the part once inserted into pin gauge As long as the gauge can go into the part, it is in spec. Bonus Round Remember the further you are from MMC when it is referenced in the feature control frame, the more bonus tolerance you are allowed. Profile of a Surface Link Enlarge. Total Runout Link Enlarge.

Profile of a Line Link Enlarge. May 6, at 2: May 6, at 8: May 12, at 1: November 4, at 1: November 18, at 8: November 7, at 9: July 28, at 7: August 3, at 2: September 6, at 2: September 6, at September 21, at May 18, at 1: May 20, at 7: May 19, at May 22, at 9: May 22, at May 26, at May 27, at 9: June 17, at 4: June 17, at 6: June 29, at 1: June 29, at 4: June 29, at 5: June 30, at 4: July 15, at July 18, at August 6, at 5: July 28, at 5: December 24, at 3: August 6, at 1: August 16, at 9: August 21, at 4: September 4, at 9: August 26, at 7: September 3, at 7: September 29, at 5: September 17, at 4: September 29, at 8: September 30, at 7: October 2, at 8: October 6, at 3: October 16, at October 25, at 2: November 2, at 3: November 3, at 3: November 18, at 9: November 5, at 7: November 10, at 5: November 13, at 9: November 25, at 3:

Pokies Meaning Condescending Meaning

Bonus Tolerance in Stack Up Analysis