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TIR and ruout or total runout 2

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ozzkoz

ozzkoz

Mechanical
Aug 13, 2009
51
Hi, I am dimensioning an o-ring grove and parkers catalog says the max eccentricity is .002 and states this is TIR between the groove and adjacent diameter. I think TIR is total indicator reading, but is this total runout (two arrows) or circular runout (one arrow)?

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Ha ha Kenat!! That's true!

But this all brings up a good reminder to designers: the relationship of a datum to a prior datum on the drawing should be established. For example, when a pilot hole is called out as a datum for others to be positioned from, that pilot hole should still be tied back to the primary datum surface.

In the figure mentioned (D-4) the intent was to show the old datum symbol, but if really pressed for an answer, we could say that the perpendicularity of that boss comes from the title block (perhaps ±1º) and that should be factored into any functional gage...

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
 
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Or, JP, we could say that the perpendicularity is per gage-maker's tolerances as the a +/- angular tolerance (if provided in the title block) arguably only applies to surfaces (please, measure the inclination of that axis?!). Honestly, people leave way too much up to subjective and selective interpretation. One of the reasons that I advocate using a note that NON-TOLERANCED DIMENSIONS ARE BASIC, and putting a decent general surface profile; it takes another level of ambiguity away.

Jim Sykes, P.Eng, GDTP-S
Profile Services TecEase, Inc.
 
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Hi again Jim--
I agree with your comment about removing ambiguity, and profile is a handy way to do that.

Regarding title block ± tolerancing on angles, I always presumed that it applies to any angle not directly toleranced in the field of the drawing. And the old drafting rule tells us that anything that looks like 90º is implied as 90º, so why wouldn't a center line or axis fall under that rule?

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
 
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Yes, but ... the old way (typically) doesn't provide a datum reference, so it's just +/- degrees to the related feature (i.e. actual face) as opposed to the datum ... potentially a substantial difference. If there's a catch-all note tying back to a datum reference frame it would help, but then would you be checking a secondary datum feature wrt an entire datum reference frame? Ambiguity.

Jim Sykes, P.Eng, GDTP-S
Profile Services TecEase, Inc.
 
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Jim,
Thanks all for your replies. I was certainly only intending this example as a picture to represent the concept (the smallest length pilot I could find in the whole book). I you think about it you will realize that, I myself, was also hoping that you would take section 1.1.4 into account. Otherwise all you would have to do is say: "see, the ASME standard did not do it either". I suspect we all know what that is like.
Frank
 
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Frank:

You asked Jim "how do you teach students to calculate the correct VC for checking the bolt holes and to create the gauge, if you do not give the perpendicularity value of the pilot diameter to the face? (say: Fig. D-4, pg 216 ASME Y14.5M-1994). Do you really tell them it is not important?"

I really didn't see an answer to that question. The gauge for this part would be such that the part would mount on datum A with the 25.4/25.6 mm OD dropping in a hole of 25.6 ID (MMC) that is perpendicular to datum A. There is not a qualifier for datum B since there just isn't any depth to the feature. The only possible qualifier is perpendicularity - not positional.

There would be a clocking or tertiary datum C simulator of 18 mm for anti-rotation and then we would then have 4 pins of 6.4 mm (virtual condition size) for the positional of the four (4) holes.

JP stated "that pilot hole should still be tied back to the primary datum surface". I do agree and it is understood that since no other angle was shown, the feature is perpendicular per 2.1.1.4 of the 2009 edition..

Jim - you stated "we could say that the perpendicularity is per gage-maker's tolerances as the a +/- angular tolerance". What does that mean? Over the years I have had only a few people from gauge shops take GD&T with me and each one has a different shop tolerance on gauges. In each case, the tolerance is larger than expressed in ASME Y14.43-2003.

You also suggested that "NON-TOLERANCED DIMENSIONS ARE BASIC, and putting a decent general surface profile; it takes another level of ambiguity away." So we apply GD&T without any consideration to the function of the feature? The 1994 or 2009 standard does not mandate this and actually gives examples where surfaces and features of size are shown without GD&T. Figure 3-30 Page 47 of the 2009 edition is just one example.

I have been watching this thread and just had to put in my 2 cents worth.

Dave D.
 
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Not to be nitpicky -- but like Frank, I maintain that the boss in Fig. D-4 of the 1994 standard must have a tolerance for its angle, and since none is given directly then we must appeal to the title block. As Jim points out, that has its own perils, but somehow that angle must be accounted for when designing a functional gage.

Dave, I'm 95% on board with your comments. But I don't think we can just make the functional gage hole 25.6, because that is saying that perfect orientation is required at MMC. (Perfect form is required at MMC, but not orientation.) Paragraph 2.7.4(a) or (c) of the 2009 standard would be the only way to safely say that the functional gage is 25.6.

I think that para. 2.1.1.4 is meant only for basic angles, meaning that there is a perpendicularity feature control frame involved. So while the dimension of the angle is implied 90º, we still need to know a tolerance on that angle.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
 
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Dave,,
Each gage-maker shop has rights & responsibilities to use an appropriate tolerance, typically not exceeding 5% of the overall tolerance applied to the feature being inspected. If I'm making a granite mill grinding wheel then the tolerances would be fairly loose and any gages made for checking it would be looser than if it was for a precision bearing. When people tell you things like "my tolerances are looser than that", you have to maintain a view to the source and their market base; you can't make a blanket statement then that nobody uses the published gage-maker tolerances ... as implied by your comment.

Your reference to 3-30 seems irrelevant; tabulated values of tolerances for feature control frames applied directly to a feature on a drawing seems misplaced in this conversation. As for Fig. 3-29 in '09, which I suspect you meant to reference, please also read section 1.1.4 regarding incompleteness of figures when they are showing a specific concept. This figure is specifically intended to show FCF placement.

As for a general surface profile not considering the function of the part ... well, "decent" does not automatically mean "gross" or "excessive". ISO has traditionally mandated that the general tolerance be the shop's poorest capability. To me, that is rarely known and irrelevant ... I'm not going to put a +/-5mm tolerance on a chamfer just because some supplier in Asia uses a hand-file to break edges. My advice to clients is to use the most common (i.e. frequently occurring) tolerance on their drawing as the default surface profile tolerance; this significantly reduces the drafting time and communicates the exact same design intent as putting individual controls on every feature ... plus, it ensures that every feature IS in fact controlled ... the old +/- system never truly achieved that. The issue that a few people have with using the "most common value" method is making the mental leap; it's just a mental switch that needs to be toggled.
As a participant in a number of Y14.5 meetings, I can assure you that the intent of the standard IS to ensure that the entire part is defined. That means that every feature of size (excepting primary datum fos and secondary datum fos under certain conditions) must be toleranced for location. Junk features such as fillets, rounds, chamfers, etc. are still permitted to have +/- tolerancing, but it adds no overriding benefit to the product definition.

As for supporting the general surface profile philosophy, it is shown well in the '09 edition. Start with 2.1.1.2(b) Basic Dimensions. Check out 3.3.35 All-Over Symbol. 8.2.3 Profile Tolerances as General Requirements. Maybe look at 2.1.1 (e) and 2.1.1.1 also.

The argument about "well, the standard doesn't tell me that I HAVE to do it that way" always arises. In a grossly simplified interpretation, "shall, must, will" are directives rather than suggestions. These are mostly avoided to cut off legal issues except where safety is at risk. "Preferably" is about as strongly worded a recommendation as can be made; i.e. do it another way at your own peril ... not recommended...Danger Will Robinson. "May" is typically a guidance word and probably sends you in the right direction for best practices.

Jim







Jim Sykes, P.Eng, GDTP-S
Profile Services TecEase, Inc.
 
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Jim:

You stated "As for Fig. 3-29 in '09, which I suspect you meant to reference, please also read section 1.1.4 regarding incompleteness of figures when they are showing a specific concept. This figure is specifically intended to show FCF placement."

One might use this argument on all the figures shown in the standard since 1.14 appears to be a disclaimer. Does that mean that all other non-pertinent information on each figure can be incorrect? These figures are our examples and we must assume that the examples in the standard are correct.

Section 1.14 states "Numerical value of dimensions and tolerances are illustrative only" which makes sense. It also states about the lack of GD&T application is "neither reason to assume inapplicablity, nor basis for drawing rejection". That also makes sense. It does not state that the applied information in the figures can be incorrect.

So, Jim, are the linear tolerances to surfaces shown in Figure 3-29 wrong? Must all surfaces shown in figure 3-30, page 47 of the 09 edition be reflected as profiles? Is it wrong to have a feature of size with its location shown with a +/-??

Dave D.
 
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Dave,
I really owe you one here; I want to thank you for getting an answer to my apparently uncomfortable question. Your 2-cents is worth a whole lot more to me, today.
Thanks,
Frank
 
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Dave, as a trainer, do your training sample drawings 100% complete? I suspect not, because otherwise you would never get people to focus on the relevant material rather than the irrelevant items. I have worked on standards for over a decade, and continue to do so today. I know from experience and legal advice that "how to" standards cannot be nailed down to everyone's satisfaction, and the most effective avenue is to use illustrative examples. With the exception of a simple basic shape and one or two simple features, it would be impossible to meaningfully illustrate any GD&T concept within the standard while fully annotating everything.

As for linearly-toleranced stepped geometries, which I believe is what you're referring to, while strictly legal it's typically a bad practice except on junk features. My rationale is that there are no opposing points and no indication where to measure to or from ... and you and I both know that THAT subtlety can make a huge difference. For the 35.5/36 dia recess of 9.4-9.6mm depth, where would you inspect it? From any single point on the "A" surface to any single point on the bottom of the recess technically is all that you need ... vice-versa is equally legal. You may think it's irrelevant or not critical in this situation, but let's say that you're inspecting using a CMM. As programmer (offline for the sake of argument) you set several points on each face and run the program. You have point-sample data which may or may not be indicative of the rest of the feature(s). You could have hit a couple of pits or pockets and been out of spec, or maybe those pits & pockets are the only areas in-spec...no way of knowing from inspection data alone. If a profile tolerance wrt datum-A had been applied to the depth, you would have had a clear tolerance zone within which the entire surface must be contained.

It is impossible to appease everyone on the standards committees, never mind the wider population. I've caused hours of debate over whether an illustration that has been in use for over 20 years means what most people have thought for just as long. As a result, information has been stripped from some drawings because it was superfluous to the concept and confused rather than clarified. Such is standards work.

Jim Sykes, P.Eng, GDTP-S
Profile Services TecEase, Inc.
 
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Jim:

You asked "For the 35.5/36 dia recess of 9.4-9.6mm depth, where would you inspect it? From any single point on the "A" surface to any single point on the bottom of the recess technically is all that you need ... vice-versa is equally legal."

Now you are into my area - quality and measuring. I was taught so many years ago that we would come from the plane (not a single point) shown here as datum A and use a 3 point set-up 120 degrees apart located towards the circumference. Zero off the dial indicator on the created plane.

Now, I would sweep the feature with a dial indicator and all surfaces contacted must be not less than 9.4 and no greater than 9.6. I would then record the range of readings such as 9.48 - 9.54, as an example.

I am not doing anything that any CMM Operator would not perform. Of course, when I was measuring parts, the CMMs were not computerized as they are today.

The standard does not get into measuring at all and I am wondering where it states that a 1 point contact is sufficient. I have not read that but maybe you have. Where in the standard is this reflected?

Dave D.
 
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Jim,
I do come on too strong here, it is my personallity. I can imagine that J-P is relieved he did not end up training here, now he can realize how lucky he really was. I assure you all this is do more to my enthusiasm for the subject than some attempt to really disrupt. I have just finished reading through all of the posts on this site and earlier on the yahoo site to glean any knowledge I may have missed. It has made me aware of the fact that, as Ken likes to always remind us, we have already discussed many of these issues before. I really do not see where that is all so wrong but suffice to say there certainly is repetition. I have to admit once I got to my own posts I am frankly embarrassed by some of them. I am sorry if I push you or others the wrong way, I am not sorry I have, and ask, questions and like to explore ideas.
Frank

"Some like to look at the standard and say why, I prefer to think of how it could be and say why not" (pharaphrase RK)
 
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That's great, Dave, that you measure things that way but the ASME standards, indeed no standard that anyone's ever been able to reference for me, says to measure a +/- toleranced dimension from a plane. Please clarify where you get that from. You could successfully argue that it has been a "common practice", but so is avoiding stepping on sidewalk cracks so you don't break your momma's back ... equally irrelevant to valid metrology. Supported by Taylor's Principle, +/- tolerance dimensions only need a 2-point check at LMC. If I recall correctly, the '82 standard and/or predecessors referenced the caliper-rule, which cannot be considered anythying but a 2-point check.

If you are going to advocate measuring +/- tolerances from a defacto datum plane, please provide standards-based justification. Doing something because it's "common practice" doesn't make it safe or legal. It's common for people to race thru yellow traffic lights, but is it safe or legal? No. And I'd be surprised to hear any instructor actually advocate such a practice to someone who doesn't know any better.

Jim Sykes, P.Eng, GDTP-S
Profile Services TecEase, Inc.
 
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No offense taken, Frank. We all like to challenge each other, and I don't get upset about recurring questions ... it's how I learned too, and it still gives me alternative perspectives to consider in contrast to and in support of my own understanding.

I realized after posting my reply that "rhetorical" could be taken different ways. It was not intended to denegrate your question. I thought of your question as more illustrative of question re the underlying topic than an actual question in search of response.

Dave and I tend to spar in these forums because we hold differing backgrounds and therefore philosophies about some of this. I don't take offense at his comments and I don't intend mine to be offensive either. It's all good. Engineers like to "debate".
Jim

Jim Sykes, P.Eng, GDTP-S
Profile Services TecEase, Inc.
 
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Jim:

You answered my question on 2 point measurement with a question. With that answer, I must assume that there is nothing in the 94 and 09 standard on the subject.

When one gets into measuring, there is levels of confidence in the outcome. I reflected how I was taught how to measure at General Motors so many years ago and we did use planes, axis, etc. A shop floor person may only use a depth micrometer but the CMM result superseded the shop floor result.

CMMs came into existence before the wide spread use of GD&T. Yes, we tried to simulate the function of the part just as the datum structure used today. If the +/- dimensions extensively used at that time were only 2 point contacts as you claim, the layout room would only have verniers and micrometers.

Unfortunately, there doesn't seem to any intensive metrology training available or, at least, in our area. This is an area that does need standardization.

Haven't had one of these discussion with you in quite a while.

Have a good weekend.



Dave D.
 
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Figured citing '82 without mentioning '94 or '09 was a clear indication, but ok ... no, I don't recall any specific reference to 2-point checks in the '94 or '09 standard ... I'm not ready to write an '09 cert exam yet as I'm still working my way thru the book.

I haven't found a decent metrology training program anywhere; MCC (Monroe Community College) apparently used to have one, but I understand it's not as effective as it once was. The topic of a metrologist accreditation or certification program pops up every few years but the big companies won't endorse and drive it so far. Another of those things that we need, but business seems to be scared of doing properly ... no problem, keep shipping everything to Asia and India...another topic for another day.

Enjoy your weekend too, Dave. Almost gave you a shout a few weeks back when I was in your area, but it was rather rushed. Maybe next time.

Jim



Jim Sykes, P.Eng, GDTP-S
Profile Services TecEase, Inc.
 
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Dave,

You asked Jim whether the linear tolerances to surfaces shown in Fig 3-29 are wrong.

Fundamental Rule 1.4 (d) on page 8 of '09 states the following:

"Dimensions shall be selected and arranged to suit the function and mating relationship of a part and shall not be subject to more than one interpretation."

One could argue that the linear tolerances to surfaces shown in Fig 3-29 are subject to more than one interpretation when applied to real part geometry. When applied to the perfectly flat and parallel features of the drawing, the meaning is clear. But when applied to real features that are not perfectly flat and/or not perfectly parallel, the meaning is not clear. Does this make the linear tolerances wrong? It depends on your interpretation of "shall not be subject to more than one interpretation". ;^)

The considered feature is not a feature of size - there are no opposed points, no local sizes, no Rule #1 boundary, no rules of any kind. I understand that as an inspector you can't just throw up your hands and say that the requirement is ambiguous. You have to do something, so you come up with practices like the 3-point setup you described. But as Jim said, there is nothing in the standard supporting it. A different inspector might use his caliper as a step gauge and get different numbers. They're all equally (in)valid because the specification itself contains uncertainty.

If the surfaces are produced very flat and parallel, the effects of this uncertainty are minimized. Measurements taken using the 3-point setup and the caliper would closely agree. This is often the case, and so the uncertainty and risk that the linear tolerances introduce often presents no symptoms. If the assumption of perfect form and orientation is close to valid, then the linear tolerances provide a useful approximation. But let's not pretend that it's fully rigorous.

Evan Janeshewski

Axymetrix Quality Engineering Inc.
 
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