Hello Paul,

Do you know what pitch the leadscrew is please? That will help enormously in checking your screwcutting results

Item 4 The groove down the leadscrew is to provide power take off for powered cross feed

Regards Brian [ An imperial Myford man]

Afaik you can't use thread dials when cutting imperial on a metric (or visa versa). Personally I've never bothered with them for metric.

Hello Paul,

Now that I know the leadscrew pitch [thank you] I can confirm that the second gearing choice you listed will indeed produce a 20 tpi thread of 20.0025 tpi, close enough for most purposes I think. The version of 40/80 as the first reduction stage will produce a 20 tpi thread if followed by gearing of 47/37, hardly handy!

40–idler–63 on the leadscrew works well [error 0.003 tpi ] and with a 63T gear you can get most imperial pitches. My book on lathe gearing covers lathes with 2 mm pitch leadscrews. Available through Google with change from £15 it might solve several problems for you. [Gearing of Lathes for Screwcutting] ISBN 978-1-78500-250-2

Regards Brian

I have just started cutting metric/imperial threads on my Warco GH1322, and found the above by Fulmen to be absolutely correct.
I find leaving the half nut engaged and using reverse works just fine but it does require a greater level of concentration, for me at least.

Well, thanks again for that table, Paul – I've saved it and printed a copy to put in my manual.

I have found that threads I've cut as above – using the gear settings in the manual – have fitted existing components quite nicely, but I'll certainly use your table if I come across pitches not in the manual.

There are two shearpin issues I've come across, both resulting from errors of mine, that it's as well to be aware of:-

a) The leadscrew shearpin on mine (just right of the sleeved flange where the leadscrew drive comes out of the headstock) was made of not-very-mild steel, and failed to shear when I engaged the wrong feed by mistake, resulting in a bend in the apron pinion (or its shaft) that drives the saddle feed. I was able to straighten it, but lived with tight spots for over a year before I found a way to do that. I then replaced it with brass.

I had a chance to examine and test the very similar (and more recent) Chester DB10VS a few months back, and it looked as if it had a brass shearpin in the analogous position, so the factory where both machines probably originate may have done a change here.

b) If the crossslide leadscrew shearpin (which is brass) breaks, it's likely to fall into the apron gearbox, and you'll likely need to take that and the longitudinal leadscrew off to get out the broken bit – which in my case jammed the gearbox most perfectly!

Both of these issues could be fixed with no lasting damage once understood.