Making Acetal leadscrew nuts the easy way

[bkahler]

Wow, this is definitely an interesting thread!

I'm a wannabe machinist who recently purchased a used Excello (XLO) mill which is a bridgeport clone that is slightly larger and heavier. I'm in the process of cleaning it up and fixing a few things.

The X axis has backlash that I will need to address before I start using the mill. Would this application work for replacing the lead screen nut on the Excello mill? In other words will it be strong enough to handle a mill table of this size?

Thanks Evan for taking the time to post this great information!

Brad

[JeffKranz]

I think the only problem of using this idea (which I think is great) is on a used screw with some wear - any wear and the EvaNut would have problems when the less used area is used. If you cast it on the less used area then you would have backlash in the used area. I think it is easier to buy new threaded stock and make it fit to your machine and then use this idea to make the nut since those are harder to find than the screw stock.

[bkahler]

I think the only problem of using this idea (which I think is great) is on a used screw with some wear - any wear and the EvaNut would have problems when the less used area is used. If you cast it on the less used area then you would have backlash in the used area. I think it is easier to buy new threaded stock and make it fit to your machine and then use this idea to make the nut since those are harder to find than the screw stock.

Jeff, thats a good point and I'm glad I asked. I need to find out what size lead screw I have start looking for a replacement.

I do know a replacement lead screw nut is available but its $95 plus whatever the cost of a new lead screw is so using a Acetel nut should reduce my cost some and make for a better system.

Thanks!

Brad

[Evan]

That is definitely a potential problem. If the leadscrew is noticeably worn then replacing just the nut isn't going to fix it regardless of what material the nut is made from. Even so, using an acetal nut has advantages over using a bronze nut on a new screw and will be my choice.

In the case of a mildly worn lead screw casting the nut on the unworn end should result in a very nice fit on the worn portion without needing to be chased to fit. It will be tight but manageable on the unworn end since the acetal is slightly forgiving compared to bronze. Another very desirable characteristic of acetal is that it has a high internal damping factor. This should help to reduce chatter in many cases.

BTW, this also looks like a viable solution to worn half nuts.

[BMSS]

A Great idea Evan, Congratulations on your "out of the box" thinking.

I did something similar to that a year ago, though I am not trying to Hijack your post, here, I will try to give a short version of my idea. Unfortunately, I didn't take any pictures, but I suppose I can make it clear enough by explaining it.

I had an old leadscrew that I had gotten from somewhere, but I needed a nut to make it usable on an adjusting table that I was wanted to build.

Since I have been using aluminum casting for some time, I decided to see if I could cast a nut for it.
I started off by cutting about a 6" piece off the old lead screw to use in my "mold".
Since I had a pot of aluminum heating, I turned to the mold. I decided to use an old, clean green beans can,,grinning.

I filled the bottom 2" inches with my casting sand, and cutting a couple of short lengths of wire to support the top of the can central to the leadscrew.
Then using an acetylene torch, on my pattern. I put a heavy coat of carbon , thoroughly "blackening" the threads. I wasn't sure how much carbon buildup I needed, but I figured I couldn't put too much on it. Then I set the lead screw into the sand in the bean can, and used the wires to hold the top of the leadscrew in the center of the opening.

Once the aluminum was molten, I poured it into the can, and left it to cool. The next day, I pulled it all out of the can, and then chucked up the leadscrew in my lathe and turned the aluminum round, and concentric to the lead screw. Then I went to work trying to remove the old sacrificial lead screw from the aluminum. Wow, it was VERY tight, and I wasn't sure if this was going to work or not, but finally I clamped the aluminum in my vise, and got out the 18" pipe wrench. In a few minutes of work, I got it to start turning, and got the lead screw finally to come out. After washing out all the carbon from the "nut" it moved with very little resistance, and was an extremely good fit. I have used it in my adjuster table for quite a while now and it seems to work well for me. It being aluminum running of a steel leadscrew, I am not sure if it would take a lot of torque, but in my application it has worked well. I then milled the outside of the nut square, and then drilled and tapped it for mounting.
If you do any aluminum sand casting, you might give this one a try.

[jackary]

Thanks Evan for you great idea. The "EvaNut" I wonder if this will enter the machinist language like Hoover?
Alan

[Liger Zero]

Thanks Evan for you great idea. The "EvaNut" I wonder if this will enter the machinist language like Hoover?
Alan

As long as it doesn't become the Kleenex of lead-screw nuts... Try as I might I cannot come up with a Xerox joke... sorry Evan.

[plunger]

acetal nut

I would be curious to know if this would work on a tailstock nut for a 13x40 chineese lathe I am trying to fix as I cant get spares for this lathe in darkest africa. I notice we have different names for plastics and metals in different parts of the world.
www.vesconite.com is a proudly made in s africa product that has a good reputation. Would this be suitable for this application
regards eugene

[Evan]

How can you tell the difference between a Xerox salesman and a Xerox technician?

The technician washes his hands before he takes a piss.

Who knows the names and phone numbers of the most pretty women in town? The Xerox technician. (not a joke )

Inside joke: How can you tell the difference between the Canon tech and the Xerox Tech? You can't. The Canon tech used to work for Xerox.

[Evan]

Would this be suitable for this application
?

No, it seems to be a mix of perhaps acetal with PTFE. It has a melting temp of 500F which is much too high to work well.

However, you should have no trouble finding acetal copolymer as that is the generic name for the plastic world wide.

Quadrant Engineering is the primary maker of Delrin and acetal copolymer. They have a main office in SA at:

SOUTH AFRICA
25 Nickel Street,Technicon
P.O.Box 63
ROODEPOORT1725
Tel +27 (0) 11 760-3100
Fax +27 (0) 11 763-2811

[Peter.]

Wow, this is definitely an interesting thread!

I'm a wannabe machinist who recently purchased a used Excello (XLO) mill which is a bridgeport clone that is slightly larger and heavier. I'm in the process of cleaning it up and fixing a few things.

The X axis has backlash that I will need to address before I start using the mill. Would this application work for replacing the lead screen nut on the Excello mill? In other words will it be strong enough to handle a mill table of this size?

Thanks Evan for taking the time to post this great information!

Brad

I reckon it will hold up just great. I fully intend to make a leadscrew nut for my Herbert mill since the nut is part of a cast bracket which I'm never going to find a replacement for.

On the question of lead-screw wear, my lathe lead-screw is pretty worn in the middle, so I used a part of the screw that was half-way between the un-used end section and the most worn middle section. I have no back-lash in the middle with the new nut and it only tightens slightly at the extremes.

Another benefit for the home shop machinist is that there is now a method whereby a modestly skilled user can produce a leadscrew which might not be fully to form, though will be of an even form along it's length, and they can just make a nut to fit that individual screw. I see great possibilities with this very basic technique. Make a really nice job of it and get it running smoothly and it's almost good enough for home=brew CNC without the expensive ball-nuts.

[Weston Bye]

... you should have no trouble finding acetal copolymer as that is the generic name for the plastic world wide.

Quadrant Engineering is the primary maker of Delrin and acetal copolymer.

Delrin? DuPont owns the Trade Mark for the Delrin name for acetal - the rest is generic. My gear supplier was adament that for their purposes they found that Delrin provided the best quality and performance. For the HSM, the generic would do just fine.

By the way, they also said that when they needed to machine prototypes, they purchased Delrin rod from McMaster-Carr.

[Mike Burdick]

I've used that method several times myself, mostly just experimenting....

Darryl,

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

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

[Evan]

Quadrant makes a full range of Delrin products.

http://www.quadrantepp.com/default.aspx?pageid=78

Delrin? DuPont owns the Trade Mark for the Delrin name for acetal - the rest is generic. My gear supplier was adament that for their purposes they found that Delrin provided the best quality and performance. For the HSM, the generic would do just fine.

Delrin and generic acetal are not the same product. The have different properties and significantly different chemical resistance. For the purpose of making lead screw nuts either will work although generic acetal copolymer is less prone to developing porosity.

[Liger Zero]

Last time I tried to explain this I got it mixed up...

Delrin? DuPont owns the Trade Mark for the Delrin name for acetal - the rest is generic. My gear supplier was adament that for their purposes they found that Delrin provided the best quality and performance. For the HSM, the generic would do just fine.

Quadrant is just a supplier. Dupont makes the resin that I know and loath.

Now there is a HOMOpolymer and a COpolymer form of Delrin. For some applications this is a big deal.

Homopolymer is the Delrin that we are talking about.

Most (not all) of the "generic" acetal stuff is copolymer.

Consult Wiki or a material supplier for specific material recommendations.

That said... I have worked with an "internally lubricated acetal before... molded parts with it.

Evan, others: Would something like that be of use for these lead-nuts? I can track down the resin and knock together a low-tolerance shape-mold if there is enough demand for the Evanut.

I envison a blank with a pilot-hole through the center... you drill it out to your size and split it along the two molded in guidlines.