Restoring old lathes, backlash in leadscrews

**BillTodd** · 24-08-2009

The Cross-slide is likely to be a left-hand thread. Are they really 8tpi? surely both are more likely 10tpi (How are the dials scaled?).

If you have room, make two new lead screw nut for each slide thread them on the OD. drill the blocks and thread it to take the OD of two new bronze nuts. Use the OD thread to take up the backlash.

Alternatively, again if room allows, a new nut could be screwed on to the existing screw and fixed to the existing block.

Pictures would help :)

**Ross77** · 24-08-2009

Like you said one for the experts.

I'll be watching this one tho. Need to fix mine at some point.

So lots of pics please.

**irving2008** · 24-08-2009

OK, a closer inspection and the application of some cleaning cloths showed I was wrong in assuming the SuperRelm was like its smaller brother. Where the RelMac has the leadscrews working directly into the cast iron, the SuerRelm is more sophisticated and I found, after moving the tool carrier and cleaning 85 years of gunk off, a screw head. Further inspection revealed a bronze/brass nut held in by a screw - see pics.. this is the topslide, but the cross-slide also has a screw head only visible once the topslide is removed.

It is 8tpi LH x 3/8", I measured it accurately with the digital calipers. RDG do a 3/8 x 10tpi LH tap for £10 but not an 8tpi :sad:, then again i dont want to be making a new screw if I can help it...

I can move the nut back and forth about 1.0mm on the screw. And the screw's endfloat in the brass bearing/mount is about 0.3mm but thats easily rectified with a washer under the handle

How do I measure wear on the screw - is it likely to wear or can I assume the wear is all in the nut?