How to: (M) on symmetry of two cylinders

[[Ma...]]

Hello,

I can not figure out how to implement this (M) on base A to be able to evaluate it right.
Do you have any tips for me please?

ISO

[[SH...]]

I have not tried this, but it is not possible to add formula in symmetry tolerance ??
Great opportunity for parallel cylinders.... 😱

[[Ma...]]

We have older version of Calypso, so no parallel cylinders.
Can not set MMC ( MMB ) for symmetry base A. Actually i don't know how it could help to 0,6 symmetry.
Or is it written there automatically for keeping tolerance and not using TED?

[[SH...]]

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Ohh MMB 😮 😮
I think it helps, total shift in the pattern in particular direction can change the symmetry...

[[Da...]]

In ISO 2692, a material modifier on a datum is only allowed, if the datum is a feature of linear size, which the distance 63,5 clearly is not. A feature of linear size must be one internal or external (a real) feature or two parallel planes, and not any other derived one from two elements.

The MMR on the datum in this case is nonsensical.

[[Ma...]]

I really don't understand if it is correct callout - I think it's not.

But for now i'll be waiting for parts and if we will have problems to fit into tolerance, then i'll do some magic 🤣

[[Ro...]]

I get a lot of prints drawn by "Junior Engineers" that obviously just learned about GD&T, so when dealing with unrealistic Modifiers i generally just leave them out and see if the part is good without them.....
I know that's not much of an answer, and my situation is probably different than yours, where i now deal with "One time One off" parts and i don't have to deal with production anymore.

What you could do, if you need to add something is take the average of the 2 cylinder diameters and input that into a formula.
0.6 + (((get actual cylinder 1+ get actual cylinder2)/2)-31.57)

[[Ch...]]

This is definitely an unusual callout.

In ASME (not sure about ISO), if the datum letter is in line with the linear dimension, the datum is the 'symmetry' of the linear, typically a key or keyway, (or slot) etc.

There's probably a number of ways to get creative establishing this after measuring the 2 Cylinders. (cross section each cylinder axis top mid bottom, 3 points = plane..)

From there You enter this created symmetry plane as the primary datum and also as secondary datum with MMB/MMB/MMR,etc. for the secondary datum. (Optionally, if results seem high, use Datum A again as the tertiary datum in the Symmetry Characterisitc.

Good luck.

[[Ma...]]

Thanks to all - sometimes even old well-known brands gives us unimaginable drawings and it's easier to be creative on CMM then explaining them what's wrong 🤣