Reworking Sherline Anti-Backlash Nuts

The new Y axis anti-backlash nuts for the Sherline mill have a countersink on the end that fits into the saddle. The nut on the left is as-delivered (I bought two) and the nut on the right is after cleanup:

Sherline Y axis anti-backlash nuts - original vs cleared
Sherline Y axis anti-backlash nuts – original vs cleared

The thread was munged enough to jam the leadscrew; it started fine from the knurled end, but wouldn’t emerge from the countersink. This being a left-hand thread, I couldn’t just run a tap through the nut, so clearing the thread required:

  • Some tedious handwork to clear enough of a path until …
  • I could force the nut over the old leadscrew, which re-formed the thread enough that …
  • More tedious handwork could remove the debris and bent brass

After that, the OD of both nuts was slightly oversized: 0.316 inch, which didn’t fit in the 5/16 inch (0.3125) bore. So I mounted the nut on the old leadscrew, took advantage of the fact that a left-hand thread gets tighter with cutting force from the lathe bit [Edit: wrong! See comments], and turned it down just a hair:

Turning down anti-backlash nut OD
Turning down anti-backlash nut OD

Purists will quibble that I should have used the four-jaw chuck. Turns out the three-jaw has under 1 mil of runout, which is as good as one could possibly want in light of the bearings.

The X axis nuts were fine, so I suspect a recent production run had a bit of a tooling problem.

[Update: The mail brings replacement nuts that look just fine. Must have been one of those glitches. No hard feelings!]

3 thoughts on “Reworking Sherline Anti-Backlash Nuts

  1. “took advantage of the fact that a left-hand thread gets tighter with cutting force from the lathe bit”

    Really? Unless your lathe turns backwards from mine, taking a cut on that nut will try to screw it away from the chuck if it is left handed. An ordinary right-handed nut will screw itself toward the chuck.

    1. I just pulled out the old leadscrew & nut, threaded them together, lined them up like they were in the lathe, gave the leadscrew a twist, and … you’re right.

      There is no reason why that nut didn’t unwind itself into the bit, other than that I was taking my usual sissy cuts, and there’s no explanation for why I thought it was turning tighter.

      I hate it when that happens, but I’m glad you’re paying attention!

      Thanks …

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