Restoring old lathes, backlash in leadscrews

[irving2008]

Is the compound/topslide LHT?

If you are going to the extent of fitting new screws then adding dials is a must, surely?

And , if you're going to make your own nut, it'd be worth adding some kind of backlash adjustment to it (you can't adjust a tap, the way you can a split die :() .

Yes they are both LH threads. And you are right, it makes sense to add the dials, its not that much more work (!)

As regards backlash adjustment, what do you suggest? the current nut is about 20mm square so I was thinking that a 20mm cylindrical section screwed into the block and locked in place with a small grub screw. It would need to be a fine thread, maybe 20tpi. Not sure I could do that with the changewheels I have today.

Here is a rough pic...

[BillTodd]

As regards backlash adjustment, what do you suggest? the current nut is about 20mm square so I was thinking that a 20mm cylindrical section screwed into the block and locked in place with a small grub screw. It would need to be a fine thread, maybe 20tpi. Not sure I could do that with the changewheels I have today.

Sounds like a good plan to me :)

Can you get at to adjust it in place? (I can just reach the SB adjuster from the back of the crosslide)

An alternative (used on the hardinge) is a brass bar (with the end threaded in place) pressing down on the screw via the nut mounting hole (I'll add a picture later).

[irving2008]

Neat approach there Bill, but sadly the lug on mine goes into a blind hole in the slide and it would involve modification of the slide itself.

I actually measured the screw accurately last night and its actually 7/16" not 3/8", although if I am remanufacturing it makes little difference. What matters is finding some leadscrew of around that size and a matching tap for the nut at a reasonable price.

I have decided that the screwed in section I previously suggested would be hard to manufacture as I have no means to thread it at the moment. So I am going with the split nut and screw idea previously discussed

[ptjw7uk]

Have you considered casting a nut thread using moglice not any idea how much it costs but an idea.
http://www.moglice.com/articles/repl...tethebook.html
(see figure 14)
I suspect you would need a new length of threaded rod to replace the screw.


Peter

[irving2008]

Have you considered casting a nut thread using moglice not any idea how much it costs but an idea.
http://www.moglice.com/articles/repl...tethebook.html
(see figure 14)
I suspect you would need a new length of threaded rod to replace the screw.


Peter

Peter, I've looked at this stuff before, but its hard to get in small quantites. I did wonder about using plastic epoxy metal and packing the nuts, oiling the screw, screwing it in and leave to set... might contain the backlash for a while - worth a try maybe

[irving2008]

Took the other leadscrew (cross-slide) off today. Its identical to the topslide one, although at some time in the past somone has lopped 7/16" off the brass bearing and inserted a (poorly machined) micrometer dial and attempted to solder a pointer (now missing) to the brass sleeve.

I now have everything ordered I need to do this except some 7/16-10 LH leadscrew, wanted to find a UK source as the US source is 10 days shipping and was hoping to make a start this weekend. Kingston Engineering don't go down to 7/16, their smallest is 1/2 but this won't fit through the holes in the slides :sad:

Anyone know of a UK source for 400mm or so 7/16-10 leadscrew? I wanted to go metric but although MD have 10x2D LH at 99p/100mm I cant get a 10x2D LH tap at reasonable cost unless someone has one they can lend me...