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:
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:
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!]