Play in motor shaft

[procarve]

one side of my x car is a little sloppy and can be wiggled just a bit even with the control powered up

i took the motor off to check the pinon and first thought there might be a little play between the pinon and motor shaft but that seemed ok.

i took the pinon off the shaft and there is actually a small amount of play in the shaft in one direction before you can feel the motor engage. not a lot, but enough that you can feel.

is this normal or do i have a problem with the motor? my cut quality is pretty good, but there is definately some chatter - not sure if it is related to this or the fact that i am pushing a pc router a little hard.

this is a new prs standard

Thanks

[richards]

William,
The gearboxes on Oriental Motor gearbox equipped stepper motors may have a little backlash. Of the four PK296B2A-SG3.6 motors that I have on my testbench, all of the motors have barely detectable backlash - meaning that I can just barely feel some movement from the gearbox's shaft when the motor's rear shaft is locked. Oriental Motor publishes tolerance specifications for their motors and their gearboxes; however, I can't find that particular document for the PK296 gearbox motors. But, bottom line, it is normal to have a small amount of radial play in the gearbox. It is also normal to have axial play in the shaft. Axial play (in and out motion) would normally be less critical because the spur gear and the rack can tolerate axial play.

Most likely the chatter marks you're seeing are NOT related to the backlash. Chatter marks that I've seen are usually clearly defined marks about 0.125 inch apart. The linear movement that could be caused by backlash would be closer to 0.01 inch, or less than 1/10th the spacing of the chatter marks.

[procarve]

Thanks Mike -

My chatter is definatley larger than the .01, I just figured I would ask.

Any idea on why one side of the gantry would be sloppy but not the other side? About the same amount of slop all along the xrail, and i don't see the pinon moving in the rack when I take up the slop by hand (a little hard to see though)

Thanks again,

Bill

[richards]

I've marked a single line on my V-rollers and spur gears with a permanent marker so that I can tell at a glance if everything is turning properly. By watching the V-rollers along the entire axis, I can easily see if there are any spots where one or more v-rollers isn't making good contact.

[rob_jones]

William, I was testing for play in my pinions and noticed that my X axis can jiggle a little bit. I have a brand new PRS-S Buddy Benchtop. From what I could see on mine is that the pinion is definitely tight, the pinion gear isn't pushed right up against the rack gear fully so they don't mesh tightly causing some play.
On mine there is a threaded rod connecting the frame to a pivoting plate that the X axis step motor is attached to. You can adjust the two nuts on either side of the pivoting plate to cinch it up tighter to the rack gear... just not too tight. I'm sure there must be a spec for this, I would be satisfied with not being able to jiggle it by hand with significant force. Either way, I think the play it introduces is negligable when machining an expanding medium like wood; atleast for me.
I hear the V bearings are mounted on a cam so you can adjust their tension against the rails too allthough I have not played with them yet. Hope this helps.

[procarve]

thanks guys -

I am going to mark the rollers - that is a smart idea, and make sure I snug the pinon up tight when I put the motor back on.

Not too worried about it, for what I am doing the cut quality still seems acceptable.

Bill