Profile dimension

[Lepage]

Hello everyone,
I’d like to know how I would go about dimensioning profile in PC-DMIS 3.5 MR2? Is a best fit alignment a requirement? If yes, then under what circumstances what decide whether it should be in 2D or 3D?
See attachment. Thanks!

[Matthew D. Hoedeman]

If it is FORM and LOCATION, then you must stay alignment to the datums in the FCF (ie ABC or whatever).

[Lepage]

Hello Matt,
yes, it is form and location. I know that I have to align the part according to the A (primary) and B (secondary) datum in that order and so forth. I’d like to know if I need to do a best fit alignment thereafter or not. If it is required then should it be 2D or 3D? Matt could you please be a little bit specific? Look, I even improved the attachment so that the drawing is easer to read!
Thanks a lot!

[cmmguy]

As matt said, with the location requirement, you would NOT want to use Best fit. The bestfit actually changes/overrides the alignment.

[Matthew D. Hoedeman]

If it is form and location, you can not do a best fit, you must stay aligned to ABC and report it 'as-is'.

[Lepage]

ok guys, thats just what I wanted to know. Thanks for the help!

[djayne]

Lepage,
How is the symmetry call out on this part working for you in PCDMIS? I have a similar situation on one of our parts and it is very inconsistant.

[John Riggins]

What about Datum tolerances?

If it is form and location, you can not do a best fit, you must stay aligned to ABC and report it 'as-is'.

Can't a Best Fit alignment be used after you establish an alignment using the datums IF, after Best fitting, the datums are still within the allowed tolerance for the datums?

[Lepage]

djayne,
the symmetry in this program has been working out good, and has been consistent. Symmetry in general remains very tricky to dimension at best. I’ve had other situations where it hasn’t worked out at all.