Maybe you guys can answer this relating to probing. A number of shops here probe parts after machining. Results are always fantastic- parts are 'perfect' within 1 or 2 microns for hole positioning and size for example (these are small watch sized parts).
Often however, when assembling, rather significant errors are sometimes evident and when checked these errors can be .01-.04mm for a tolerance callout of +- .002mm. That's a lot!
Seems to me if the part is probed on the machine that made it, in the same setup, any errors in precision inherent to the machine will be duplicated, giving essentially perfect results. Would make more sense to me if the part were rotated 180 degrees and then probed. If suggested this to a couple of shops but get a blank stare.
Could very well be that I have no idea what I'm talking about
, but to me it makes sense. I have zero CNC experience, never used a CMM; I just know that the protoype parts made on my jig borer often seem to go together better than the production parts that follow.
The machines are all late model Swiss or German high precision CNC's specifically designed for the small work involved.
Sidenote: I'm not looking to discuss why the machines are not holding the tolerances- just the technique in probing which seems to be blind to the errors.