We have a part that is calling a Profile to be Datum A. The shape of this profile looks like a potato chip, so I believe this would covers all 6 degrees of freedom. I created a lot vector points on the surface and did a best fit alignment to it.
My problem is this, how do I define this as Datum A when I create geometric tolerancing?
After you align, you can make generic features (three planes) for X, Y and Z. Name them A, B and C and use those in your GD&T if that's what you are needing.
You just can't apply MMB on them. If you are counting on MMB for some reason, it won't work.
We used to make a partial knee that resembled a potato chip. I talked the customer into creating datum target points to use for the alignment of the part. The iterative alignment worked like a charm and made the implants so much easier to measure.
And more repeatable across multiple machines and programmers.
This is the ideal method, but we aren't all lucky enough to get customers that have engineering time to spare for fixing lax designs.
I have a couple that will and more that won't.
At that point, second best, get on the phone with the CMM programmer at the customer and agree on the alignment method (and target points if applicable).
Unless you are even luckier and the customer just doesn't care (I had a friend that made the buttons that you push at a crosswalk, lucky sob). I am extremely jealous of those people lol