Screwcutting Acme threads

In which case because of the backlash in the train it will rip the previous threads

In Delrin he might get away with a 5/16" boring bar with the tool sticking out the required 1/8" or so and by taking things steady, steady. Or could always mount the Delrin on the cross slide and use a slender boring bar between centres.

The heat and squeeze method is sounding better all the time.

No apologies necessary Michael - it's fine. I just wanted to clarify my intention in asking about ACME threads in view of your comment. Nonetheless I appreciate your courtesy.

Hopper - brainfade eh? Tell me about it! Thanks for your further suggestions - I think it should be possible to get a tool in to cut an internal thread in Delrin at this pitch/diameter (especially if the thread is only 0.09 deep). The heat'n'squeeze method does seem the best way forward though.

I'll be getting a look a the leadscrew tomorrow.

Robin.

I have made quite a few Delrin nuts with a variation of the theme on Home Shop Machinist, published by Evan Williams but he pinched the idea from a guy over on Practical Machinist and wouldn't give him credit for it.

My method is slightly different in that the two previous methods you had to split the nut and force it round the screw.

I made mine with the bore of the nut the same as the OD but tight, in other words a pre-stripped nut. Cut the middle man out.

I think this sketch explains it better.

Basically you thread the 'new' nut over the screw, drop unto a tapered cup and fit a ram piece. This then goes onto a press and the cup and screw is heated with a hot air gun whilst pressure is applied.

This has the advantage of making it one piece and with a bit of experiment on how far you press the cup in you can choose what fit you want. Something the squeeze in the vise method can't do.

AFAIK this method is my own and I have not seen it repeated anywhere else.

Because at one time I had loads of ball screw thread offcuts from cutting long screws down i even made some Delrin nuts to fit these screws. Not as good as ball screws by any means but certainly better than Acme screws.

Again nothing new here Moore International make screws and nuts such as these and call them Ronda screws.

Any Google Child can find them.

[EDIT] There should be no gap between the ram piece and the top of the screw so as the ram piece is pressed down it carries the nut and screw with it so it cannot push the threads.

This is one made by the split method as it needs jacking screws for adjustment.

This is an 8 start thread off one of Mr Rollsie Royces test jigs in the crack detecting department.

Their guys couldn't make a new nut

Edited By John Stevenson on 19/10/2016 00:18:37

Nice one, John. If no hydraulic ram I suppose lesser mortals could rrange a means of pulling it down with threaded jack bolts, or even a threaded cap and suitable washers beneath.

I have progressed from my initial findings (of melting acetal and casting), thu drill core size and squeeze, to this method over a few months.

The heat and squeeze method is still more appropriate for Richard's half nut, I think, but yours for round is good. Next logical step might be whether a lathe leadscrew nut might be made in all delrin (with just a metal insert for the holding bolt/screw), rather than using delrin as an insert in the old worn out body.

Edited By not done it yet on 19/10/2016 08:15:40

A slight digression, if I may:

MarchantDice [who I think probably know better] are listing this on ebay **LINK**

http://www.ebay.co.uk/itm/TR12x2Dx600mm-2mm-Pitch-Trapezoidal-Acme-Ballscrew-Leadscrew-Fine-Pitch-/311308776672?hash=item487b72f4e0:m:mKxSqvo3Vh7GwWiplZX-0tg

So far as I am aware: Trapezoidal does not equal ACME, and neither form qualifies as a Ballscrew.

MichaelG.