Evaluation setting on Profile using free form

[[Th...]]

Hi, I'm not well versed using free form to check a profile of a feature. In the free form evaluation tab, choosing best fit and creating an alignment from that will make the measurement result to be better. My question is do I use best fit or not and when is it appropriate to use best fit? Thanks

BEST FIT.JPG

[[Cl...]]

I struggled with this recently. I was told by Zeiss applications that it is only to be used when the profile
is to itself (no datums). However, I did recently use it to get me to pass a type-1 GRR, referencing it in
a secondary alignment to allow rotation around the Y axis.

In other words. Surface profile callout of a pocket to Datum -A- (cylinder), both along the same (Y axis).
No clocking datum. So, I created the best-fit and alignment allowing rotation around Y. Then I created a
secondary alignment using -A- as my rotation in space (Y+) referencing that best-fit alignment.

I hope that makes sense. This was explained to me by Martin Jansky. He's more familiar with this than I am.
Maybe he'll chime in. I will add that I do not know the difference between Gauss and tschebyscheff.

[[Ma...]]

If you can wait i'll help. But it will take about 9 hours to get to work to be more precise with tchebyshev.

If you have not datum for FF you can choose no datum/alignment in profile callout. This will trigger bestfit.
If you have fully defined datums for profile callout, then you can not use bestfit at all.

Any specific question?

[[Th...]]

Thanks that answered when it's allowed to do best fit. The feature is datums defined.