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:
X axis leadscrew hole counterbore
On the Y axis:
Y axis leadscrew hole counterbore
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:
Loosening leadscrew bolt
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.
#1 by George Martin on 10-July-2012 - 09:12
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?…………………….
#2 by Ed on 10-July-2012 - 09:19
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…
#3 by George Martin on 10-July-2012 - 09:51
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!!!
#4 by Ed on 10-July-2012 - 14:54
Ooooh, I could use Pumpkin Glitter again!
#5 by max on 23-January-2013 - 00:57
Cannot you put the lead screw in it then knock with a piece of wood to remove the nut?
#6 by Ed on 23-January-2013 - 06:20
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.
#7 by sod on 24-January-2013 - 01:38
Yeah, the worn out one you were replacing. :-)
#8 by Ed on 24-January-2013 - 07:54
But, but … [splutter] … it’s not that worn out …
I have this problem; some days it’s really bad. [grin]