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Parallelism with MMC

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By [Ca...] ,
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[Ca...]

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Lets pretend I have a callout, it's a 1.500±.005, with a .005 parallelism at MMC.

How do I add MMC to parallelism?

I have half a memory about creating a bogus diameter from the actual 1.500±.005 length, and it gets fuzzy from there....

Thoughts?
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[Ri...]

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1.500±.005, with a .005 parallelism at MMC. If the 1.500 dimension is the width of a gap between the considered feature and the datum feature then 1.495 would be the MMC. Right click on the Tolerance field in Parallelism and click on Formula. The formula will be the actual width value, either from a distance or from location, minus 1.495, then that value plus 0.005

It might be a good idea to describe your method of determining MMC bonus in the comment field.
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[Aa...]

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Not to be a pedant here, but a plane isn't a feature of size. Ergo, material condition modifiers can't be applied to tolerances applied to planes.

If the two planes are nominally parallel, then together they form a width, which is a feature of size, and the 1.500 +/- .005 is the size tolerance on the width.

Rule #1, the Envelope Principle, says that at MMC, perfect form is required on features of size. There ways to override this rule and relax form control. 5.4.2.1 of Y14.5 describes the appropriate method for the situation at hand. Treat the 1.500 +/-.005 as a width. Apply a flatness tolerance of .005.
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[Jo...]

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Is the parallelism applied to a single plane, relative to a datum plane or is it applied to a width relative to a datum plane that is NOT one of the walls of the width? If it's the former then it's a bad callout. As someone previously said, you can't modify a surface at MMC. If it's the latter then maybe what Richard said will work considering Calypso doesn't even give the option for parallelism at MMC.
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[Ri...]

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No it doesn't and Parallelism of two Planes in Calypso would be calculated as a single Plane relative to a Datum Plane, which makes MMC troublesome. My thinking for this was as the distance of the two planes deviates from the minimum allowed distance, the amount for the Parallelism of the considered Plane could increase. Another, perhaps more appropriate solution could be to ignore the MMC but then inspection risks rejecting good parts. My solution utilizes MMC with a rational (maybe) reason. That's why I suggested making a note in the comment field describing the method for calculating bonus.
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[Ja...]

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Aaron, I don't have a copy of those standards. Can you post them here (if it's legal)? As far as I know you can't add a modifier to parallelism. If you do, it becomes profile. I'm sure that's why Calypso doesn't have that capability.
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[Jo...]

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You can modify an orientation tolerance with MMC as long as the feature being controlled is a feature of size and the tolerance is associated with the size dimension. The tolerance then applies to the axis or centerplane of the feature.
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[Aa...]

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I'm not sure how much of the standard I could legally post.

What John said applies to straightness and flatness, too, in Y14.5.

ISO 2692 also has examples in Appendix A of applying MMR to orientation tolerances.
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[Me...]

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The parallelism characteristic will allow a non-cylindrical feature of size to be modified if it’s created with the “Symmetry Plane” feature. Since the tolerance applies to the center plane of the feature, form error will need to be excluded. This can be accomplished by creating a copy of the symmetry plane via “Recall One Feature”, and using it to evaluate the orientation of the center plane with applicable modifier.
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  • 1 year later...
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[Mi...]

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As I was reading this thread and saw the actual call out I was thinking that the callout wasn't to a single plane but to the distance between the 2 planes and that a plane symmetry would be the solution. Didn't even think of recalling it into another symmetry to account for form error. This gives me something to research, I've had several difficulties with similar problems were this may be a solution in those cases as well! Thank you.
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[Da...]

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I knew it's worth it, to revive 1/2 year old thread 🙂
No rush Michael, but when you discover something, please report back!
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[Mi...]

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I just did. I had a profile on a plane that was called out to a single datum plane. It was giving me trouble by introducing form error from the datum which was in turn created by recalling 4 separate planes. I created a new plane and recalled the datum plane into it and used that plane as the datum. Didn't change it much but it helped.
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