depends on what your datums are, and also the amount of tolerance.
I had a part that was fixtured in place by 4 pins, to create my datum A i measured holes that were actually the four pins, but i added sample hits to measure the surface of which the pins went through, to keep from having my holes wander in space.
i used those measurements to create a plain for datum A, then created a line from 2 pin measurements(that i had already measured), created a center point on that line and that gave me B and C Datum.
mind you this may not be the best, but i made it work and my result were repeatable. my tolerance was +-1mm and .5mm down to +-.25mm in some places
depends on what your datums are, and also the amount of tolerance.
I had a part that was fixtured in place by 4 pins, to create my datum A i measured holes that were actually the four pins, but i added sample hits to measure the surface of which the pins went through, to keep from having my holes wander in space.
i used those measurements to create a plain for datum A, then created a line from 2 pin measurements(that i had already measured), created a center point on that line and that gave me B and C Datum.
mind you this may not be the best, but i made it work and my result were repeatable. my tolerance was +-1mm and .5mm down to +-.25mm in some places
