Originally Posted by
TomH,ShopBot
For all the motors sold over the years the pinion shaft sizes have been .5", 12mm or 14mm, just depends on the motor model.
normally to make sure you get the correct pinions we will ask you for the motor model and the rack width. since they are machined bore pinions the fit can be tight on some of them. I'm certain that if it were the wrong size pinion you would not be able to hammer it onto the shaft at all, there's at least a half millimeter difference...but I won't say that it isn't possible. I don't have the motor spec sheet with me so you'd have to shoot support an email to confirm everything is right with your motor model-pinions.
it sounds like you need to replace the keyway and the setscrew as well.
if the shaft itself has too much damage (and the issue is appearing in the X axis) we can do a simple test. if your Y axis or Z axis motor is the same model, swap one of them and their pinion/keyway with the X motor and see if that tightens up the x (and possibly causes a problem in the other axis but will tell you the issue)
With the pinion on or off, motor unmounted and power on, does the click back and forth you hear translate to a discernible amount of play? very small amounts to play are normal even in low-backlash motors and don't often translate to discernible differences in cut quality with most bits/operations with normal stepover.
there was a time where using a dial indicator to measure the amount of play an axis has seemed like a good method to measure and correct overall play, but overwhelmingly using the push-pull method is the most practical. if push pull doesn't find anything then the issue often is elsewhere (like motor/pinion/rack engagement, tool level, YZ car square/plumb)