So our 1994 Haas VF-3 recently started clamping tools at the wrong spindle orientation, which is very bad because the spindle taper has protruding drive dogs that are supposed to index on the toolholder. Clamping out of proper orientation makes the tools stick out an extra 1/2", spin, vibrate, and do all sorts of bad things. From reading the service manual, it sounds like the machine not being able to consistently stop at its home orientation is caused by a worn out shot pin that locks orientation at the home position, but actually clamping in the wrong position without throwing a spindle orientation error seems like something that would be caused by an encoder ring being loose.

My question has to do with a motor / gearbox replacement that was performed a year ago (but only about 500 machine hours ago). These encoder and shot pin components are swapped over to the new motor / gearbox from the old one during this procedure. Does it seem more likely for the cause of my problem to be simply worn out components or improper installation by the technicians who did the motor / gearbox swap? We now need to get the spindle replaced due to some damage caused to the taper and drawbar by a spun tool, but are unsure whether we can trust the same company to do this work if they may have installed the encoder assemblies improperly before.

Any help trying to sort through this issue will be greatly appreciated. Also, any general information on how the machine verifies its home position when performing a tool change would be very helpful.

Thanks!