The Y axis on my Sherline CNC mill has developed about 8 mils of backlash, a bit more than seems reasonable. Some poking around shows that the anti-backlash nut is loose while in the middle of the leadscrew and snug while at either end, which suggests the leadscrew thread is also worn. That’s no surprise, as I didn’t figure out that having a bellows over the leadscrew was a Good Thing until, let us say, considerably later than I should.
If I must replace the leadscrew, I may as well take the whole XY assembly apart, clean everything, and replace the consumables. So I ordered a sack o’ parts from Sherline; they’re all cheap and readily available. The overall index has the exploded diagrams and the parts list for my mill boiled down to:
- 54161 Y axis leadscrew (9 inch)
- 50140 Y axis anti-backlash nut
- 50200 Y axis nut
- 50171 X axis leadscrew
- 50130 X axis anti-backlash nut
- 40890 X axis nut
- 50150 anti-backlash lock
The only gotcha: nowhere (that I can find, anyway) is it written how to get the leadscrew nuts out of the stage. It turns out that the holes through the stage aren’t uniform: the X narrower on the right and the Y on the front, so you must drive the X axis nut out to the left and the Y axis nut out to the rear. The counterbore is visible just behind the anti-backlash nut if you know what to look for, so you’re driving the axis nut away from the backlash nut.
On the X axis:
On the Y axis:
Trust me on this: you cannot drive a 5/16 inch nut through a 19/64 inch counterbore. If you have a 19/64 inch transfer punch, that’s a dandy way to get the nuts out.
The easiest way to loosen the socket head cap screw holding the flex coupling to the leadscrew is to grab the coupling in a lathe chuck (with the leadscrew protruding into the headstock) and then apply the hex key:
They used red (high-strength) Loctite on all the leadscrew bolts, as well as on the tapered joint between the leadscrew and the flex coupling, and on the bearing preload nut… so I will, too.
The Smell of Molten Projects in the Morning 
Blue Loctite242 (I think) is the one to use. It’s removable.
Red Loctite in permanent. It takes heat (as in torch) to remove. How do I know?…………………….
Now, I ask you, what could possibly be wrong with applying fire to a project? [grin]
That said, cracking the preload nut loose required quite a bit of torque. The residue was definitely red, so I leaped to the conclusion that Sherline likes the high-strength juice in that situation.
I’m also leaping to the conclusion that threadlocker colors are consistent across manufacturers…
One other technique is to put finger nail type (lacquer) polish on the threads. Let it dry and then assemble.
Red Loctite is evil to get off!!!
Ooooh, I could use Pumpkin Glitter again!
Cannot you put the lead screw in it then knock with a piece of wood to remove the nut?
Only if you don’t mind beating on a leadscrew… [grin]
The nuts had a surprisingly large burr under the lock screw and put up quite a struggle to remain in place. I think they should just slide right out, in which case the leadscrew will work fine.
Yeah, the worn out one you were replacing. :-)
But, but … [splutter] … it’s not that worn out …
I have this problem; some days it’s really bad. [grin]