fmmv Posted June 14 Share Posted June 14 I thought I'd just post this on here in case there are folks wanting to get rid of backlash on lathes etc, and this helps. The idea is to make a new leadscrew nut from delrin, and instead of cutting the thread, it is formed by squeezing the delrin round a warmed leadscrew. I have a Denford 280 Synchro lathe, and parts are generally no longer available. My inspiration was from the Denford site here. This method is for their slightly smaller Viceroy lathes. The backlash on the cross slide was about 0.2mm,not impossible to work with but annoying, and mainly caused by the leadscrew and nut. I started with an offcut of 50mm delrin rod. I thought I would leave it as wide as possible to help strength - I could always turn it down. It was too fat to fit the space in the castings so I faced and centred it in a 3 jaw, switched to 4 jaw and faced a couple of flats onto it. I did not want to follow the denfordata method exactly by splitting completely as I was concerned that it would be weak on the underside of the nut, where it has to be quite thin , so I bored it and split it from the top of the block but just to to the bottom of the bore with a junior hacksaw. I then gently-ish warmed the block with a hot air gun, and prised the split open and managed to get the cleaned and oiled leadscrew in. I then clamped it in the vice and warmed the leadscrew as per the denfordata method. I had to get the leadscrew quite hot before the delrin could be be clamped totally over. Getting the leadscrew from the lathe for this meant dismantling the saddle so I wanted to be sure all was well before putting it all back to finish. I left the delrin clamped hard in the vice overnight and it seemed to have formed a reasonably solid join. Getting the screw out was hard, and once out I ground 2 small cuts in the end of the leadscrew to chase the thread. After a few passes with oil, cleaning the cuts each time, it worked reasonably smoothly. Then it was back to the4 jaw, and turning it down to fit its location. Having got this far I was rather scared of falling at the final fence. The original brass nut fits in a hole in the cross slide and is retained by a downward conical pointed grubscrew driving a horizontal pin outwards. I decided to just use the split that I had used to get the leadscrew in and drilled and tapped a vertical hole, but used only the first tap so the grubscrew tends to expand the delrin as it's driven in. So, does it work? Yes it does, slightly stiff by comparison with the original worn brass nut but backlash is way down, from 0.2mm to 0.03mm. And that lash is not in the screw and nut, it is in the bearings for the handwheel for which I need to find a way of adjusting. Even if you didn't want to use a delrin nut long term, it would let you use the machine to make a new metal replacement part (not sure I can cut an internal LH acme thread to be honest). Overall I'm happy. 2 Quote Link to comment Share on other sites More sharing options...
sean f Posted June 14 Share Posted June 14 Nice idea, not sure how long it will last but unless you are using the lathe all the time probable long enough for hobby work. Might also be worth a look at the Accu.co.uk site, they sell lead screws and nut in various sizes, if you can work out what you have and its not something weird then they might have something. Quote Link to comment Share on other sites More sharing options...
vulcan bomber Posted June 14 Share Posted June 14 If you have time to worry about 0.2mm of backlash in a lathe you've got time to start another hobby.. 2 Quote Link to comment Share on other sites More sharing options...
fmmv Posted June 14 Author Share Posted June 14 Fair enough, what would be considered an unacceptable amount of backlash? Quote Link to comment Share on other sites More sharing options...
vulcan bomber Posted June 15 Share Posted June 15 10 hours ago, fmmv said: Fair enough, what would be considered an unacceptable amount of backlash? Never really thought about it, as long as you always turn your handles in the correct direction for it, it doesn't cause a problem 2 Quote Link to comment Share on other sites More sharing options...
smallfry Posted June 17 Share Posted June 17 On 6/15/2024 at 12:33 AM, fmmv said: Fair enough, what would be considered an unacceptable amount of backlash? A whole turn ? Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted June 18 Share Posted June 18 23 hours ago, smallfry said: A whole turn ? We're into Land Rover steering territory there Quote Link to comment Share on other sites More sharing options...
vulcan bomber Posted June 18 Share Posted June 18 On 6/17/2024 at 11:16 AM, smallfry said: A whole turn ? I've worked a lathe with around a turn and a half of backlash in it and still got decent jobs from it. Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted June 18 Share Posted June 18 35 minutes ago, vulcan bomber said: I've worked a lathe with around a turn and a half of backlash in it and still got decent jobs from it. That's nothing, I used to have to work a lathe in a cardboard box in a layby with nowt but 3 rats on a treadmill for power - and we were LUCKY! 1 2 Quote Link to comment Share on other sites More sharing options...
fmmv Posted June 18 Author Share Posted June 18 Didn't realise you'd worked for Britpart 4 Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted June 19 Share Posted June 19 16 hours ago, fmmv said: Didn't realise you'd worked for Britpart Only briefly until they got rid of me & the lathe and just used the 3 rats to nibble out shapes from the Chinese scrap metal directly... 1 Quote Link to comment Share on other sites More sharing options...
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