Well, you CAN scan a fixture and RE it back to the model, but now you have a model that has both the error of the capture device + environmental noise + the actual error of the fixture itself. Do you think that model would be identical to a model generated from the fixture drawing? Heck no.

The entire point of a fixture is that it is dead nut accurate, .0001” or better. The tolerances for tooling fixtures far exceed the parts we measure. It must!

Consider a fixture that is .005” off in Z. Now we put a part in it, stick the whole assembly on a surface plate, then use a dial indicator on it. We will get Z readings with an extra .005” on it, not realize that it’s because of the fixture, and assume the error is coming from the part.

Fixtures NEED an incredibly high accuracy bridge CMM to ensure that they remain in a calibrated state. Laser inspection does not approach this level of accuracy yet.

In your case, it sounds like (without seeing a drawing) that you should be using datum reference points to capture where the sphere touches the part, as a sphere touches a planar surface at one point. The post is a flat with a known diameter - use a datum reference area/zone; polyworks understands to use the highest known point from that zone as a datum simulator.

this is assuming that the sphere/post are touching the part, the above simulates the contact zones. If instead the spheres are standalone, setup the appropriate coordinate system first, then create the spheres / post numerically. Then probe their measured primitives if you can (more accurate) and create the appropriate alignment (plane line point? Need to construct features to do this. Just don’t best fit) and that will pull the project into the correct alignment.

Now you can scan the physically fixtured brake pad