Making a Nut to Fit an Oddball Acme Screw?

[Crunch]

I need to make a nut to fit an odd sized Acme screw (if it wasn't an odd size, I'd simply buy a nut).

 

What I was planning to do was:

1. chill the Acme-threaded screw

2. coat its threads with nickel-based high-temperature anti-seize

3. heat a doughnut-shaped piece of steel to forging temperature

4. slide it onto the Acme screw, and

5. beat on it on my anvil to shape threads on the interior of the donut-shaped piece of steel.

 

(The nut doesn't really need to be square or hex-shaped for my purposes, and the nut will not need to be strong enough to take much of a load when in service; it will simply be used for positioning.)

 

Does this sound like a decent plan of attack?

 

Anything I should watch out for?

 

Thanks in advance for any tips.

 

 

 

 

 

[ciladog]

I don’t think your plan will work because as you ‘beat’ the doughnut on the screw it will just stretch and get larger as if you were working it over the horn of an anvil.

 

The easiest way to make an Acme nut is the way vise screw boxes used to be made.

 

Get yourself some square stock (like key stock) or forge out some square stock that is the same size as the threads on the screw.  Heat that stock with a torch and wrap it around the screw at the minor diameter.  When you have enough wraps (the length you want) unscrew it off the screw.

 

Measure the outside diameter of the thread you just made.  Take an all-thread coupling and drill it or bore it out to that diameter and braze the thread into it.

[Jason @ MacTalis Ironworks]

might  work, but I'd personally take a cold 6 pack to a machine shop...

[doc]

Another way to do it is to get one of the many castable resins made today and cast your nut. Cover the screw with oil, paraffin or some other release agent and us a paper tube around the screw as a mold. I've seen half-nuts for lathe lead screws done this way. Or use some sheet metal as a mold and cast it from babbitt.

[Crunch]

I don’t think your plan will work because as you ‘beat’ the doughnut on the screw it will just stretch and get larger as if you were working it over the horn of an anvil.

 

Thank you for your reply... Maybe I wasn't clear.

 

The Acme screw is actually more like a machine screw than a wood screw in the sense that there is no tapered end on it. It is square on the end. There is no point or cone at the tip like there is on the tip of the anvil's horn.

 

So I wouldn't be beating the "doughnut of steel" to make it larger...I would be beating it down to make it smaller, after it already had the Acme-threaded rod going all the way through it.

 

In other words, I would in effect be swaging (with a hammer rather than a press) the "doughnut of hot steel" down around the threaded part, and using Acme-threaded rod as a "mandrel," so to speak.

 

My theory is that the plasticity of the hot steel, when it is beaten over the mandrel of the Acme-threaded rod, would allow threads to be "molded" in the interior of the "doughnut of hot steel." 

 

I believe forged Weatherby rifle barrels are made this way: A hollow tube of hot chrome-moly steel is swaged, or forged, around a mandrel rod which has a "positive" of the rifling in it. 

 

Do you still think it won't work?

[Revtor]

Still think it wont work..  The "nut" will get larger and sloppy.

 

 I'd cast it from liquid titanium epoxy or something like that.  You could make the shape of the "nut" whatever you'd want, cast in holes etc.  Ciladog's idea is great if the thread is large enough.

 

have fun!!!  let us know how you get on with this

 

~Steve

[ciladog]

Crunch, I understood what you wanted to do but hot metal doesn't act the way you think it would in this instance. If you could press that doughnut on all sides at once in a spring swage and a press, it might work but hitting it over a mandrel (which is what that threaded rod would be) will make the hole larger, not smaller. And you may damage your screw.

 

You could always try it and if it doesn't work move on to something else.

 

[Crunch]

Well, darn. Now I get it. 

 

I wonder whether crushing it in a vise over the Acme rod would give the same results...sounds like it would. That's a disappointment.

 

Maybe, instead of a "doughnut" of hot steel, I'll try using a "C" shaped piece of hot steel that's not quite long enough to wind all the way around the threaded rod...maybe by beating on it, that'll lengthen it enough to span the full circumference, and then I could weld the two ends together. There's gotta be a way...

 

Thank you all, again, for your replies. 

 

 

 

 

[ciladog]

Why don't you post a picture of the screw with some measurements and we can all get a better look at what you are trying to make.  There were some good suggestions posted that you seem to be resisting.  Is that because of your skill leavel or maybe your understanding of what was posted.  This is not a hard thing to do being that it is not going to carry a heavy load.

[SmoothBore]

Without sounding too "preachy", ... there's a reason ( or 10 ) why nuts are not formed in the way you describe.

 

I suspect any introduction of hot steel, will have a negative effect on the male thread.

 

 

Before assuming a nut is unavailable, I'd want to determine what thread it is, exactly, ... and then determine it's availability.

 

I often single point unusual threads in the lathe, ... because I CAN, ... not because there's no alternative.

 

 

 

.

[dablacksmith]

i would go with some type of casting method ... less possability of damage to the threads and it is a proven way to do things if it is not on a vice i would use a lead or tin and cast it on the threads (with a suitable releaseing agent) if it requires more strength i would go lost wax pattern and cast in bronze but allow for shrinkage .. good luck! forging a piece to use as a nut would be hard unless you have a extra threaded rod then you could use a piece as a top die and use a swage block c shape as bottom die hammer it down into your piece .. make two half pieces and weld um together ... it will mess up the piece used as a die  tho.. 

[JNewman]

I have to agree it will not work and I question whether any epoxy will work either.  I would check the dimensions again you might be surprised you may be able to find a matching nut at one of the large industrial suppliers such as MSC or Mcmaster Carr.  If not you could try Babbitt which will not be terribly strong but I think will work better than trying to forge a nut. 

[doc]

Check out this link for some solutions;   http://www.practicalmachinist.com/vb/general/half-nut-repair-226759/

 

and here is another        http://bbs.homeshopmachinist.net/threads/43645-Making-Acetal-leadscrew-nuts-the-easy-way

[Stephen Olivo]

If you are looking at making one why not make a tap.   This can be forged and filed to fit the thread your working with.  I came across the part of a book in which he explains how to forge and file a tap for a thread as I was doing some research last night. The book was The Woodwright's Workbook by Roy Underhill.

http://www.uncpress.unc.edu/woodwright/index.html

Then you just drill (or punch) a hole through a peice and tap the thread into it.

[John B]

Some facts regarding the screw's diameter, and any other useful information such as pitch, width of thread, and the use it is to be put to, would help enormously in deciding a suitable way to tackle the problem. 

[Ricko13]

I have access to a nifty piece of software that calculates threads with no issues. If you give me some dimensions, i can find a standard for it. Really important to know the major diameter an pitch (thread per inch). And if you can measure the minor, that will also help a great deal (major dia - (2x thread height)=minor) to determine if it is a stub or general acme.

Our shop is making quite a few internal acme threads right now if ever you need something done, PM me.

[Bill Farmer]

DIDN'T ANYONE SEE THE PREVIOUS SUGGESTION OF TAKING THIS TO A MACHINE SHOP???? I CUT NUMEROUS ACME THREAD SCREWS/NUTS AND IT IS REALLY NO CHALLENGE IF YOU'LL JUST TAKE IT TO A MACHINE SHOP, OR EVEN A HIGH SCHOOL SHOP. I HAVE A PERFECTLY MATCHED SCREW/NUT COMBO. MADE IN A HIGH SCHOOL MACHINE SHOP TO RESTORE A LEG VISE IN THE SHOP AT FORT BOONESBOROUGH'S FORGE.

[Backwoods Blacksmith]

You would be surprized how many machinist have never turned an Acme thread. Also a 3/4 or even 1 inch dia id  Acme can be a pain. But you are right a machined thread is the best way to go unless the shaft thread is badly worn or streached.  In that case the shaft threads will need to be  trued up and a nut made to fit..  If it were me and a machinist was not avaliable I would go to Enco and get Acme thread stock and a nut to fit and replace both at the same time.

[thingmaker3]

When you say "odd size," do you mean "metric?"