Assembled gearbox binding despite all parts in tolerance

I assembled a gearbox with gears, shafts, and housing. Each part individually measures within spec. But when I assemble it, the gears bind and don't spin freely. I tried using feeler gauges to check clearances, all good. I also swapped out the bearings for new ones, no improvement. The binding seems to occur at specific points in rotation. Could it be a cumulative tolerance stack-up causing interference? How do I diagnose and fix this?

#MotorSelection# #PLCProgramming# #Automation#