Making Acetal Leadscrew Nuts the Easy Way

• #one

HMEM,

I had to terminate working on my first IC engine and tear down my Diamond horizontal mill's table. The leadscrew nut for the y axis is shot. There's no gamble of me finding a replacement anywhere as information technology has an odd outside shape and so I was going to get ahead with turning 1 myself (using the lathe and non borer).

I've done internal acme threading one time before though it was over 10 years agone now.

My first question would be:

Is it brass or bronze and what blend should I try to buy. I'll need a piece of one.75" square stock two.25" in length so it'southward going to be pricey

The side by side question:

Practise I demand to lap the nut to the leadscrew? I read something virtually it online but don't know if that's something I really need to do or not. If so should the threads exist cut slightly under finished....? I approximate that wouldn't work though because the leadscrew wouldn't thread in....? Or is that just for leadscrew nuts that have adjusting screws on them...?

Thank you in accelerate for any advice or guidance y'all can offer.

-J.Andrew

P.Due south. Almost forgot the leadscrew is a iii/iv"-10RH Acme thread.

• #iii

Goldflash,

Thanks but unfortunately nobody makes a nut with a large enough OD to allow for milling down the bottom alignment dominate.

Here's a quick model of the nut since I don't take information technology here to take a photo:

No commercially fabricated nuts take enough meat on them to mate upwardly.

As well not enough clearance on either side of the existing nut's diameter to allow ane to press in a new nut. It's going to have to be made.

Thanks,
-J.Andrew

• #4

Concluding edited: Aug 13, 2014

• #6

Crankshafter,

Thank you a bunch for the very interesting link! I don't think it will piece of work for this awarding because the fabric between the flat mounting surface and the bore is fashion also thin to exist made of plastic. I volition exist filing this method abroad for later use though on other leadscrew restorations! I can't believe how good the backlash numbers came to be!

Goldflash,
I did find a tap on ebay already just it's $95 plus aircraft! The internal threading won't be too much of a problem for me assuming I tin can find out about the whole lapping question.

Thanks all,
-J.Andrew

• #8

Thanks bb218.

I guess I will consider buying that $95 tap. The thread depth for this nut would be 0.074". That's quite a bit of rubbing for a 2.25" deep hole...

Did you use brass or bronze? And which alloy?

-J.Andrew

• #10

J:

As far as lapping probably not.
in lapping an abrasive is added to a soft material similar copper or lead and it smooths the hard material.
some new parts aer lapped together with an abrasive that breaks down this would be better, but you have an quondam sooth lead screw and will accept a new part.

The actetal method is an interesting one I take not seen before.

Anther option is Molguise (SP) or other machine repair epoxy.
diameter out the damaged threads and cast new ones from epoxy.
But IIRC a epoxy lit will run as much every bit the tap.

I have a friend that went through a like set up IIRC he did cease upwards making a new role.
as far as material selection

http://world wide web.mcmaster.com/#standard-bronze-alloy-sheets/=t9eq3d

IMHO 936 aka C93600 would be a skillful pick easy to machine and you tin solder or braze and then you lot tin add the boss and buy a much smaller piece

You may be able to phone call one-888-Dura Bar and they should be able to provide the materiel and advise for the all-time material.

http://www.dura-barms.com/dura-bar/index.cfm
Tin can

• #11

I would brand it out of bronze and consider a small modification.
Make it a couple of threads longer if possible, then slit ii threads radially 3/iv of the manner and place two screws squeezing the saw kerf.
That provide a backlash adjustment.
Make certain the slit is located such that the entire nut is loaded in the positive direction of movement and the 2 threads are loaded in the back direction.

• #12

Is there enough "meat" on the original nut to bore it out, plow up a threaded sleeve and insert it in the hole? That is the way I reco'd the half-nut on my old Drummond lathe. Soft soldered it in position and information technology'south worked for years.

Don't be scared of screwcutting Summit threads. It is pretty easy in contumely or statuary 660. Utilize the biggest diameter deadening bar that will fit in the hole (.600 or so for a 8 tpi iii/4 Meridian). Grind a HSS cut tool much similar a parting tool but expressionless flat on tiptop, no back rake.
Make sure the leading flank on the tool has the actress clearance to clear the helix angle of the thread (examination this by inserting the bit into the thread on the lead screw and eyeballing it.
Make the width of the tool tip to the width of the thread, plus a grand for clearance.
Strop the cutting edge to a fine terminate on an oil stone. Taper the width of the tool narrower as it comes back from the tip, to give chip clearance. Allow the very tip do all the piece of work.

Have the cutting tool sticking out just plenty to cut the full depth of thread plus a few m for chip clearance. Then take .010" cuts until yous become down to petty finishing cuts. Test the thread by screwing the leadscrew into it before taking it out of the lathe, and take more tiny cuts if needed.

No need to lap.

Brass vs bronze. Information technology depends. If the leadscrew is hardened then bronze is fine. If it is hardish, and then 660 bronze possibly ok. If it is not hard or hardish, you tin can use contumely and so it wears but does non wear the atomic number 82 screw.

• #14

If your nut is worn out, you should consider making a new spiral.
You near likely, will not like the feel of the loose and tight spots in the travel.
That is what I have constitute over the years. Just trying to salve you some grief.
Skilful luck

• #16

I think Hopper has told y'all everything you need to know but I will add that I have repaired large nuts by casting white metal around the pb screw.
This gives a good fit and lasts a very long fourth dimension as well.

I always wondered if this would piece of work, sounds like a quick fix worth trying!

• #17

The depth of the thread at two.25" long is tough with a bore of. 670" or so. A tap is the tool for this type repair.

Get a chunk bronze 660 and mount in a lathe, or apply a tiresome head with a reversed cutter to mill a stem, so bore the hole and run the tap through.it will be a long tap vi".

• #xviii

Thanks all for the input. I'm probably going to attempt without a tap. The only tap in that pitch I can find is $95 used on ebay. No sign of long taps either.

For now I cleaned everything and re-installed the nut with a slightly showtime bushing on the tail stop of the leadscrew. Information technology misaligns it just enough to take the nasty slop out. It's a temporary fix until I accept some time to make a new nut.

Information technology's a funny coincidence the simply fourth dimension I e'er did meridian threading was in the brusque lathe schoolhouse in the Navy and I happened to do the exact same thread pitch (3/4"-ten) for my terminal project. It was too in contumely. At least I know it can exist done.

Cheers once more. HMEM members seem to be a good deal more helpful than any of the other machinist forums out there.
-J.Andrew

• #19

Expert lad. Accept a become. All you take to lose is short piece of bronze worth a few dollars. A .625 diameter boring bar should well exist up to the job, and provide enough fleck clearance. The secret is all in careful tool grinding and honing, making certain there is plenty clearance on the front, sides and height of the tool. And that it is oil stoned precipitous sharp abrupt. One of those jobs where the grooming volition take longer than the chore.

lusupen1955.blogspot.com

Source: https://www.homemodelenginemachinist.com/threads/fabricating-leadscrew-nut-questions.23407/

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