spindle movement, unround holes

[bbortnick]

Hi,
Wondering about some things (related?) with our shopbot prsalpha 48x48.
1) Small holes made with profile CUT are slightly oblong and therefore one dimension is a little smaller than the requested dimension.
2) When changing bits in the middle of a file, it's very easy to move the spindle, loosing your x/y position. I can reset with proximity locations, but if x/y was elsewhere, it's very hard to restore to that spot.

Everything seems tight on the gantry, but is the most likely cause of oblong holes worn pinion gears?
Is there a method to changing the bits in the middle of a file that does not risk moving the spindle and loosing your x/y?
Thanks for the help!

[coryatjohn]

I have a 2013 PRS Alpha and when the system is powered up, the gantry is solid as a rock. No way to move it at all. I've changed bits hundreds of times and never lost position.

I suspect your machine needs a little TLC. When was the last time the pinions were changed and/or adjusted? They are a wear item and have to be changed every so often. If they're loose or worn, you'll have a lot more slop in the system.

Try shaking the gantry with the power on and the reset button pressed. At that point, the motors are energized and should lock the gantry solid. If you detect any movement or even a clicking sound, then there's too much slop in the system and something has to be adjusted or replaced.

[bbortnick]

Thanks for the tip! - can you point me to a pinion adjustment/check routine?

[bbortnick]

I should mention I hit the red stop switch and the key is removed from the control box (which powers the VFD/spindle I believe) during a mid file bit change. Note that I have found the shopbot docs on checking play and replacing pinions.

[coryatjohn]

I suggest refraining from hitting the red stop button during bit changes. It's not only unnecessary, it also cuts power to the motors, rendering them free to move. All you need to do is remove the key to access the wrench.

The purpose of the red stop switch is to immediately cut power to the system in the event of an emergency, such as the being caught in the machine or having the machine do something obviously wrong (like crashing into the work). I've used that button maybe twice in a decade and both times it was due to a screwup on my part.

[bbortnick]

Hi,
So I removed all the spindles to inspect the pinions. All 3 of the x/y pinions were a little loose on on their shafts: I don't know if the key, or the slot in the pinion is warn out, but it was not holding the pinion stationary. I tightened all the set screws and that removed the slop. I am guessing that will not last, however. Should the pinions be rock solid on the shafts with they key, and the set screws not yet tightened? check out the video:https://photos.app.goo.gl/emoixKN1oYmB7U8z9