Runout equivalent for a non-cylindrical form
Runout equivalent for a non-cylindrical form
(OP)
I am wondering how best to dimension a part with the following characteristics. It is shaped like a short shaft with a bore down its length and a series of rectangular keyways cut full length into it. The keyways are equally spaced, so it is essentially a splined shaft with rectangular grooves. I want to separately control the distance from the keyway bottoms to the axis of the bore and the variation of that same distance; I want to have a tighter tolerance on the variation of the dimension than on the dimension itself. It would be akin to the runout tolerance except it's not a cylindrical form. How can I do this?





RE: Runout equivalent for a non-cylindrical form
(1) Make the bore datum feature, say A. (2) Use basic dimension for the distance between the axis of the bore and the keyway bottoms. (3) Apply the composite profile callout. The upper segment (with looser tolerance) referencing to A will control the distance between each bottom and the axis A. The lower segment (with tighter tolerance) containing no datum feature references will control variation within the pattern of bottoms.
RE: Runout equivalent for a non-cylindrical form
RE: Runout equivalent for a non-cylindrical form
With that being said, I am afraid I don't have any decent solution at the moment other than the suggestion to use an additional drawing note (or even an extra view) and specify precisely what is acceptable and what is not (especially when speaking about the tighter requirement).
RE: Runout equivalent for a non-cylindrical form
It's a shame total runout is not defined in a more general way so it could be applied here. I think I'd favor such an expansion of definition over adding the new dynamic profile modifier. The current application would just become a special case, so you could have full backward (or is it forward?) compatibility.
Thoughts?
pylfrm
RE: Runout equivalent for a non-cylindrical form
The part is chucked using the axis reference, and rotated until the the first flat meets the angularity to the axis using a dial indicator. Set the indicator zero at either the high or low spot. Then the part is rotated 90 degrees, do not reset the indicator, and the total variation is used to verify the angularity while the difference is used to verify the allowable difference. Repeat 2 more times ensuring that the total variation from the axis is not exceeded.
<soapbox>
How many drawings already have notes that describe acceptance of some part exactly the way a new modifier will?
If it aren't many, then is there a lot of value in adding more baggage versus getting users to think through the process and write out what they want to accomplish? Either way, someone will not know these edge cases and have to grab the reference, so placing that directly on the drawing seems best.
I expect it will get as much usage as datum modifiers for customized datum reference frames do, which is not much.
(Can someone, for goodness sake, do a replace of 'invoke' with 'use' I know someone there has a thesaurus and they should have it taken from them. Invoke, verb: cite or appeal to (someone or something) as an authority for an action or in support of an argument. Using stilted language isn't the same as using it correctly.
"a customized datum reference frame may be invoked." No, it cannot be invoked. Stop it. From https://www.vocabulary.com/dictionary/invoke : To invoke is to call up something such as a law, a higher power, or even a ghost. In court, you might invoke the Fifth Amendment (the right not to say something that will make you look bad) if you don't want to talk.)
</soapbox>
RE: Runout equivalent for a non-cylindrical form
For example, how many times did you think about the "continuous feature" idea (along a shaft with grooves cut into it) before you saw the 2009 standard?
How many times after?
That's the value (assuming the modifier is explained clearly when first introduced).
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Runout equivalent for a non-cylindrical form
In my previous job (I was there for 6 years) I never had a chance to use a runout tolerance (for example), because items I was dealing with had no cylindrical features. I never had a chance to use 80% of things defined in Y14.5. So does that mean runout tolerances and the 80% of other things should be gone from the standard? Of course not.
Going back to the original question, both ideas (pylfrm's and 3DDave's) still require some kind of a note to clearly express design intent. In the lack of standardized tool, I would lean towards mixing them, that is to apply 'nX' directly toleranced dimension with looser toletance from the axis to the flat (a drawing note would have to really precisely explain interpretation of this dimension) and also use profile of a surface wrt A with the tighter tolerance value with 'nX' prefix. In absence of a basic linear dimension between the datum axis and the flat this would mean (at least on 2D drawing) that the pattern of n profile tolerance zones would have to stay a polygon, but its overall size (across flats) would be free to shrink/grow.
3DDave,
In my opinion angularity tolerance will not work because as an orientation control it does not fall under simultaneous requirement rule. In other words, with angularity tolerance used 4 flats may be perpendicular to each other but do not necessarily have to form a square - each flat may be at different distance from the datum axis, and the variation of that distance will be controlled by directly toleranced dimension with looser tolerance, which is not what OP wants.
RE: Runout equivalent for a non-cylindrical form
<soapbox>
pmarc, I didn't come close to suggesting that every one needed to be used by every user, just that it should be frequent enough that the general population would see some benefit.
</soapbox>
RE: Runout equivalent for a non-cylindrical form
Of course it (4 flats nominally perpendicular to each other controlled by angularity tolerance) falls under '2009 2.1.1.4 Implied 90° or 0° Basic Angle. But it does not mean that 4 angularity tolerance zones must/will create a square.
Picture an as-produced part that has each pair of two adjacent flats perfectly perpendicular to each other, but the distance between opposed flats #1 and #3 is 1, while the distance between opposed flats #2 and #4 is 10. This will also meet the angularity tolerance suggested by you.
In OP's case, of course, such difference in distances between opposed flats will not be possible because that distance will be controlled by directly toleranced dimension with a looser tolerance, but this still will not be enough, as OP is trying to keep the variaton in distances within a tighter tolerance.
<soapbox>
Well, "frequent enough" is a very subjective term. To me a couple opportunities per month is pretty frequent.
In this thread http://www.eng-tips.com/viewthread.cfm?qid=415186 you seemed to disagree with the committee's decision about removing concentricity and symmetry from the future version of the standard. May I ask how often have you seen true functional need to use these two characteristics? If I remember correctly, you once gave us really great real life example of concentricity tolerance application, but you probably must have seen much more valid applications since in your opinion concentricity and symmetry deserve to stay, right? (BTW, I agree with you that they should stay).
</soapbox>
RE: Runout equivalent for a non-cylindrical form
"Then put a 4X dimension to the center with a flag note indicating which center is to be used, such as the Datum Axis used in the angularity tolerance and, in that note, set the maximum variation among all 4 measurements."
Again - it is the need of the general population. I've had need to represent a tolerance zone in the form of a complex equation, but I don't expect that method to be added to the standard, even though it would make most interpretation problems go away in favor of inspectors using scientific programmable calculators.
Adding rotational symmetry to the standard would also fix this particular problem.
RE: Runout equivalent for a non-cylindrical form
Regarding the comments on customized datum reference frames: I was not familiar with the concept, so I studied up in the ASME Y14.5M-2009 standard and it struck me that if one could set up a customized datum reference frame using a cylindrical coordinate system, then doing what I wanted without notes would be possible. But I suppose that would be too esoteric of an extrapolated application of the concept to be useful.
RE: Runout equivalent for a non-cylindrical form
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RE: Runout equivalent for a non-cylindrical form
RE: Runout equivalent for a non-cylindrical form
Answering to your previous post with the attachment, I would say that equivalency between the two illustrations is at least debatable.
Personally, I see potential issues with the |prof|0.05|A| callout on the illustration on the right. It may be unclear to some readers (including me if I did not know the intent of the callout) as to whether basic linear dimension 34.29 locates this 0.05 profile tolerance zones or not. That is why I suggested getting rid of this basic dimension and go with the solution on the left.
But now, as I think of it more, I would see another option - modification of the picture on the right by just adding 'BASIC 34.29 DOES NOT APPLY' at the end of 'VARIATION AMONG ALL LIKE FEATURES' notation. I think that would solve the problem and would be much more GD&Tish than applying directly toleranced dimension 9X 34.29+/-0.10, as shown on the left illustration.
RE: Runout equivalent for a non-cylindrical form
Yes, of course you are correct. The fact of the basic dimension also applying to the tighter surface profile tolerance slipped by me. As an alternative to your 'BASIC 34.29 DOES NOT APPLY' idea, would the use of a customized reference frame that shows only rotational constraints in the tighter tolerance work? See my illustration, attached. Did I correctly apply the constraints to the degrees of freedom in this example?
RE: Runout equivalent for a non-cylindrical form
I would say that the customized datum reference frame concept, as shown in your latest attachment, will not produce equivalent requirement to the 'BASIC 34.29 DOES NOT APPLY' idea. Since A constrains only two rotational degrees of freedom, there is no requirement for the pattern of nine tighter profile tolerance zones to be centered as a group on datum axis A. Your idea, in combination with the other profile callout, actually creates a requirement pretty similar in meaning to my first proposal in this thread - composite profile tolerance. The difference is that I initially suggested using no datum feature references in the lower segment of the callout.
In general, I don't think that the customized datum reference frame concept will be useful in this particular case. The intent is to have the pattern of tighter tolerance zones centered on datum axis with additional ability to shrink and grow freely within the larger profile tolerances while staying regular polygon. That additional shrink/grow ability is not what the customized datum reference frame concept was designed for.
Some additional comments/remarks:
- if the tolerance for 34.29 dimension is +/-0.10, then the profile tolerance value defining nine larger tolerance zones should be 0.2 not 0.1.
- when the customized datum reference frame concept is used, there is no need to explicitly list degrees of freedom in those feature control frames that actually don't override any DOFs (see geometric tolerances applied to datum features B in figs. 4-45 and 4-46).