Additional MMC

the B & C (M) are not the same as the one for the tolerance. For the B&C, it is datum shift, not bonus. (and, IMO, that is backwards, the tolerance should be before the datum callouts)

Matthew D. Hoedeman is correct. The callout is backwards and the tolerance should come before the datum references. However, ignoring that, this is how you are supposed to approach this in PC-Dmis....


I assume you have a recent version that uses the geometric tolerance command?

You firstly need to add a geometric tolerance to control the relationship of B to the higher precedence datum A. This tolerance will be used to calculate the MMB boundary for the secondary datum B(M).
Next you must add a geometric tolerance that defines the relationship of C to the higher precedence primary datum A and secondary datum B(M). This tolerance will be used to calculate the MMB boundary for the tertiary datum C(M).
Lastly, create your geometric tolerance from your screenshot. PC-Dmis will look up through the routine for datums B(M) & C(M) and use that data to calculate the MMB boudaries for the A|B(M)|C(M) datum reference frame.

refer to Y14.5-2009 Fig. 4-16 and para 4.11.6.1

Yeah I'm not sure who drew the print, I agree. Now from doing a little looking myself, does what you said pertain at all to to the Deviation tab that you get in the position feature? I've seen posts about it but if I'm not mistaken it's not a feature you ever really want to use. I'm assuming that what neil.challinor said about how to dimension it is going to be the way I should do it?

Yup, what neil said. I don't use "new" Pcdmis, I'm all legacy, so datum shift isn't anything I use (and for 99% of what I do, even if it is on the print, it is impossible to use it).

The MMC on the tolerance (Ø.010 M in your example) is a bonus against the size of the feature, and it applied directly as the deviation from the condition (MAXIMUM material condition in your example) to the actual size of the part. Add that to the tolerance.

Any modifiers to datums are so simulate what could be done at assembly.

Say you are putting together a crappy shelf thing from Walmart.

You start all the screws and fastners, but you don't tighten anything down. Then you get to wiggle it it best fit all the screws so they ALL go in.

If they all go in, the MMB on datums B and C in your example covered the issue.

If they all go in, then the parts are out of print.

There isn't easy math you can do to calculate what this is. And it is to be applied completely, you shouldn't be datum shifting +.010 on B for feature 12 and -.005 on B for feature 40. You can't do that with the shelf, so you can't do that with the part.

(there is some wiggle there based on exactly what is assembling, hoses can move more than a steel L bracket.)

The MMC on the feature tolerance is making allowance for big screw holes and small screws giving you more wiggle while you assemble those shelves, as the screw and hole have more air in them.

Can someone show me an example of what that callout would look like dimensioned in a CMM program?

Nice explanation!

Can you tell us what the datums are?

I am assuming -A- is a plane...What are -B- & -C-? Are they coaxial holes or are they holes that are going into the face of -A-??

I use legacy dimensions, if you give me some more info I'll whip up what I would do on the hex block model & share the code

Yes -A- is a plane, -B- is center of the part and -C- is a timing hole at a specified radius and angle off the part (~14.02 dia. for -B- and -C- is at R7.400 and angle of 1.5º.

the visual would be greatly appreciated! I'm struggling to define this correctly in PCDMIS and I know I should be able to get the answer I know is right!

ok cool, you're gonna wanna use an offset line

you look that up & i'll whip something up, ttys