Hello - I purchased a used Woodworker that looked well maintained. When first rebuilding it on the QCW…and manually pushing the X rail backwards to the rear I could sense and hear a “wobble”…e.g. the leadscrew resistance was not consistent on the left side Y axis.
Once assembled the same Y-axis motor intermittently failed to move and binding would occur. I found the RCA for that issue was a cable pin that had migrated in the plug.
Once assembled, powered, homed etc. and running the Y axis forward and backward, visibly the the leadscrew is wobbling. The opposite side Y axis lead screw is flat. You can hear the vibration caused by the wobbling lead screw.
So….assuming that I am dealing with a bent lead screw caused by the binding previously noted…I removed the lead screw and checked the straightness…and it looks good to the eye and with a light source. I certainly am not seeing the ±1 to 2mm or more wobble that was present when in operation…easy to see the wobble.
I then focused on the lead screw nut (the bearing that moves due to screw rotation). The white nylon/plastic wipers connected to it are oblong in shape due to wear (?) and the orientation of the wear is vertical which matches the wobble orientation. I could tell via teh set screw indents how they were mounted.
So my question to the community is what is your experience to the wear pattern of the lead screw nut or the white plastic wiper? Do you recommend I have the lead screw tested via run-out before proceeding? Replace the lead screw nut? Others tests?
Thoughts appreciated.
Have you checked the bearings that capture the ball screw in the aluminum block? It is possible that they are worn - unlikely, but an inexpensive solution to check. Did you happen to check the ball screw nut to see if it was applying the correct tension? I believe Onefinity recommends tightening until the washer can barely be moved under the nut.
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Working on your ideas I rebuilt the Y axis assembly (and I repacked the screw nut just for fun). Note: the lead screw ball nut would freely with no play move along lead screw when free of the mounting blocks…so I had faith that the ball nut is “ok”.
Once reassembled and mounted with the X axis off, the resistance and wobble is present. I focused on the ball screw nut that is in the operator-side of the assembly. I found that with no torque on the bolt (the washer can be moved with a small amount of resistance) that the Y-axis travelled well, less noise and wobble. As soon as I applied torque to the ball screw nut and applied torque until the washer can move (but it takes force with the edge of an Allen key for example) the noise and wobble is back. This supports your suggestion that the lead screw bearings in the mounting blocks are the source….not able to handle the wee bit of lateral force.
I will disassemble and replace the 4 bearings and will update the results.
Thanks
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The root cause of the lead screw wobble was the bearings in the end blocks. The bearings are under a bit of lateral stress due to the tension of the lead screw end nuts. The old bearings had lateral play and also had some points of wear/stickiness. I replaced the 6804RS bearings that are 32 mm OD, 20mms ID and 7mm Width with ABEC 5 rated bearings. Speed is not a factor of course…..just wanted the tolerance and hopefully a longer life.
For newbies (such as me) that have not had a CNC before and therefore are not aware of how easy or difficult the unloaded axis should operate….with the new bearings in place and appropriate leadscrew end nut tension (the wash can be pushed and will move) the axis carriage (?) can be pushed with one finger under moderate force and the noise from the leadscrew assembly is consistent and not very loud. This test is with the motor attached as well….if the motor was off things would be even smoother.
Before the bearing replacement I had to use 2 hands to move the carriage and the noise was periodic and loud. The lead screw would flex when the end bearings provided resistance.
Many thanks for the good advice.
CMc
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