Making Acetal leadscrew nuts the easy way

[Paul Alciatore]

Evan,

Once again you did it my friend. Great technique and thanks for sharing. I am definitely going to try it for the cross slide in my SB when I get my shop moved. With a new screw, of course.

[clutch]

Evan,

I don't want to reread all this. Is this your nut for the cross slide?

Will you post an update after you have some time on the nut to let us know if it was a good idea or a great idea?

Clutch

[Evan]

It's a great idea. I have been using acetal lead screw nuts on my CNC mill Y and Z axis from day one and they have almost no wear. In contrast, the bronze nuts on the X axis need adjustment frequently.

[clutch]

It's a great idea. I have been using acetal lead screw nuts on my CNC mill Y and Z axis from day one and they have almost no wear. In contrast, the bronze nuts on the X axis need adjustment frequently.

Excellent, the application I had in mind is a X? sized mini mill. I'll know which one right after I can afford one.

Clutch

[Dale Lusby]

If I were to press this into a metal bracket how much oversized should I machine the acetal? It would be about 1.25" diameter. Would the same press fit tolerances be used as recommended in the handbook or more or perhaps less?

[Evan]

Don't rely on press fit alone to hold a plastic part in metal. The coefficient of linear expansion (and contraction) is around six times higher for most plastics compared to metals. Always use some sort of positive mechanical method to permanently fix the part in place. Glue, pins, threads or other means work. Delrin and acetal glue well with cyanoacrylate glues.

[plunger]

acetal nut

would this stand up to the abuse of a tailstock on a 13x40 lathe drilling say a one inch hole in a piece of steel in a home shop environment?

[Evan]

It depends on the size of the nut and type of thread as well as the engaged length of thread.

[alsinaj]

making acetal leadscrew nuts the easy way

Looks as if this method would also work to make linear motion bushings at a fraction of the cost of commercial units. Just use a piece of polished rod instead of acme thread. And the rod wouldn't have to be round, either. It would be nice to be able to make fully supported linear slides in decent sizes (say, up to 6') without paying for Thomson rails and bearings. Thoughts, anyone?

[Toolguy]

Delrin Evanut

I just made one for the Y axis on my 8 X 18 Kent surface grinder and it worked out very well.

[Evan]

I have some more experiments in mind thanks directly to Darryl's suggestion of using graphite powder on the screw. It may well make for a better fit with no need to chase it and may also provide some additional lubrication. Another possibility is to lubricate the screw after forming with spray on PTFE resin and run the nut over that while still quite warm. PTFE will form an "alloy" with acetal so it may incorporate it into the surface of the threads. One more possibility that I think may have promise is to tightly wrap the threads with a layer of PTFE plumbing sealing tape before forming. There is a lot of room here for experiment and possible improvement.

[Rigger]

Talking to Sir John on the sat phone today and he mentioned he'd experimented a while ago after seeing Daryl's post on PM and managed to do some without doing them in two parts so no change of it splitting in two and he'd formed these onto spare lengths of ball screw to make a plastic "ball nut"

Apparently it's not new as a company in the UK makes and sells these.

Rigger

[Evan]

I had an e-mail from a John a few days ago and he has a raft of leftover pieces from ball screw shafts. He said he was going to play around with it to see what he could come up with.

[Robin R]

Another posibility for coating the leadscrew, before forming the Acetal around it, might be a Molybdenum Disulphide product. A couple that look like a possible fit are Molyslip ADF, http://www.molyslip.com/products/spe...ying-film-adf/ and Molyslip Moly Powder. http://www.molyslip.com/products/spe...p-moly-powder/ The molyslip ADF might bond to well to the leadscrew to release well, but I think it would work to spary it over a coat of wax polish. The Moly Powder actually lists leadscrews among the applications it is suitable for.

[Evan]

I though of Molyslip but I hate the stuff because it migrates faster than spotting ink. I used to service equipment at a molybdenum mine and the entire place was a uniform shade of dark gray including the surrounding trees and landscape. It was a very monochrome place, very strange to see.