Making Acetal leadscrew nuts the easy way

[Evan]

According to Quadrant they make Delrin. From the link above:

Delrin® Acetal


Delrin, a homopolymer acetal, is also manufactured and stocked in rod and plate. It offers slightly higher mechanical properties than Acetron® GP Acetal, but may contain a low-density center, especially in larger cross-sections. Copolymer acetal also offers better chemical resistance than homopolymer acetal. Delrin is ideal for small diameter, thin-walled bushings that benefit from the additional strength and rigidity of homopolymer acetal.

[Evan]

A quick phone call to Quadrant EPP clears up the confusion. Quadrant manufactures stock shapes, not resin. They buy all resin from other suppliers including Delrin resin from Dupont. Because they buy the resin from Dupont they are able to use the trade name Delrin on the product.

[Liger Zero]

Suppliers change names/trade formulas/buy each other out so often I have a hard time keeping track.

Back in the day General Electric made Lexan. Now its made by Saudi Basic Industries Corp. I have found other makers of polycarbonate resin... which I encourage customers to switch to for "personal political reasons."

[Liger Zero]

zomg! double post!

[Dale Lusby]

Excellent post Evan. This will be the perfect solution to the leadscrew I am planning on making for my LeBlond T&C grinder. I also need a nut so I will be searching for some Delrin/acetal to make one of these up. I'm glad I read this one as I was going to hold off on making the screw but now this is the motivation I needed to do it.

Thinking about it I will probably have extra so if anyone has an interest in a small piece let me know and I'll sell it to you cheap. I will probably be getting 1.5" bar so I could cut a small blank of the length you need from it to mail to you. That will probably give enough diameter to machine down to the size needed.

[dfw5914]

Certainly this will become "The Way" to make accurate leadscrew nuts. Although I would call it the "EvanSqueeze Method".

Great idea and thanks for sharing.

[Duffy]

Evan:-Two points. First, using your method, would not just about ANY "cheap and dirty" acme screw stock make a perfectly acceptable set? Rather than paying top dollar for a piece of ground thread stock? Second, would this method not also make an excellent replacement set of half nuts? In some cases Keystone could provide a length of acme stock six feet long.
It sure has to be a better method than my "armstrong" tapping using a tap made from the screw stock. That worked butwas t ever a Devil to turn the tap!

[Evan]

See the last sentence in post 49 Duffy.

[lazlo]

Darryl,

I remember you talking about it way back in '05.

http://www.practicalmachinist.com/vb...ew-nuts-79338/

LOL! I guess Evan's going to have to pay Darryl a royalty fee for the "EvaNut" :

I've experimented with heat forming uhmw around a threaded shaft. I made a two sided nut by simply clamping two softened pieces of uhmw around a threaded shaft. I used some wood to make 'clamping plates' that would allow the soft uhmw to press into the threads on the shaft. The wood pieces have a shallow groove cut into each one where the shaft will lie when it's pressed in a vice or a press. The end result is a two part nut that has 'wings' which can be used for mounting the nut, and also allow you to adjust the play by skimming material off the inside surfaces of these wings. In use, one side of this two part nut can be bolted solid to whatever it needs to propel, and the other wing can either be shimmed apart some to create some play, or clamped tight to eliminate play, or have some material skimmed off then bolted together to create a tight fitting nut. Or the second wing can also be used to hold the nut to it's home in the mechanism, and both wings can be shimmed or skimmed as needed to adjust the play. Whichever would work best in the room available for the nut.

I found the initial fit to be tight without any shimming or skimming, and if anything, there needed to be a thin shim between wings to create an easier turning shaft.

It's my feeling that a nut formed this way from uhmw is superior to one turned in the lathe, in the same way that a rolled thread in steel is superior to a turned thread. Smoother threads and more accurate.

During my experiment, I determined that an accurate two part press mold would be needed, as the uhmw faithfully takes on every little offset and wrinkle in the mold. You would be looking for accuracy without a next step machining operation, as this plastic is 'springy', and will take some skill to machine to an exact size. Best to mold it to finished size right away. Having said that, it wouldn't be hard to include markers in the mold to define where to drill mounting holes in the finished nut halves.

One thing about pressing the softened plastic around a threaded shaft this way is that the shaft tends to self-center. Of course your mold can always have alignment grooves to center the shaft automatically anyway. The two sides of the mold should have some means of aligning to each other as they are pressed around the shaft and softened uhmw pieces.

One drawback to a nut made this way is that the resulting threads in each nut half don't go full depth for a full half circle, but this could be offset by making the length of the nut longer.

Something which I thought of but didn't try is to coat the threaded shaft with a graphite lube or something, prior to the clamping. The idea was that some of that lube might end up locked into the plastic, giving a self-lubricating action.

[Evan]

LOL! I guess Evan's going to have to pay Darryl a royalty fee for the "EvaNut"

Har. I have at least half a dozen unique claims. His is an example of prior art to which I have added non-obvious improvements.

Of course they are obvious after the fact to one skilled in the art but then that is always the case.

[darryl]

Make the cheques direct deposit to my bank account. I cold use deeze money. The 18 million my friend from Nigeria send me is nearly to be send, but is not recieve so soon, almost gone. I spend it on laser pointers and test plastic. For you to make Evanut from out it my frined. Such I have a great deal from you we have a joint businnes planned so trustworthy my partner. ? Let us make these nut form millions!!

[Walter]

ROFL, Thanks for the chuckle.

Evan, nice work, you just solved a mill issue for me. Well... when I get about 1/2 a dozen other things finished.

[kmccubbin]

For a worn lead screw, how about forming a nut, charge it with abrasive, and use it to lap the unworn areas? Then make another nut.

Kerry

[Evan]

That will not produce the type of flank wear typical of a worn screw. Besides, if it is bad enough that the nut won't run over the entire screw reasonably then it is time to replace the screw. It isn't difficult to cut one. Use some 1040 normalized steel for best finish and long wearing. After turning and polishing heat to red with the screw rotating as held in a drill chuck and plunge straight down into a bucket of water while still turning it in the drill. That will produce a very straight screw. Since you will be making a nut to fit the actual thread form the dimensional accuracy will not be critical. The only thing that will matter a lot is the thread pitch.

[S_J_H]

Love it! It looks like a fantastic method and I will surely try it out very soon.
Thanks for the how-to
Steve