It didn't take long for me to become unhappy with the design of my anti-backlash mod. Due to the large amount of friction, I became concerned about excess wear of the lead screw. A lot of nonuniform wear could cause problems when traversing to the extremes of the table. So I started working on a scheme similar to the approach Sherline took on their CNC mill. Their approach uses an external feed screw nut that is snugged up against the table to remove backlash. To keep the nut in place, its outer perimeter has a rather coarse knurl. A thick washer, also knurled on its outer perimeter, engages the external nut. The external nut is turned via the washer until the backlash is reduced to a low value (while keeping the drag relatively low), then the washer is fixed in place with a bolt thru its center.
Below you can see my version of this:
The round piece is the external nut (fabricated from a feed screw nut I bought from Little Machine Shop). I drilled a 1/16" hole in the nut, to engage a wire. The bracket is bolted to the end of the X-axis table. The slotted piece holds a 1/16" piece of piano wire that was bent to fit into the nut, and is fixed in place with a standoff/bolt combination.
Here's a photo of the installed pieces:
In use, the bolt is loosened so the nut can be rotated clockwise in order to remove any backlash, then tightened. Since the only force the standoff, slotted piece and wire experience is the frictional torque between the nut and feed screw, they don't need to be very heavy-duty.
With this setup I was able to reduce the uncontrolled table "slop" to about .001", and the mechanical turns dial vs. DRO indicate I have about .002-.003" of backlash. Before, there was about .005" of slop and about .010" of backlash.
The only thing I would change at this point would be to replace the Philips-style screw with an socket head screw. Right now, to adjust the backlash I have to remove the feed screw bracket to gain access with a screwdriver.
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