Straighten a acme lead screw?

Very Good information.

Regards,

The way I see it is there is no way to restore precision without replacing the screw. If absolute precision (in that axis - in otherwords relative position is is enough) is not needed then straightening (an lapping in) to the point of non-binding may suffice. Your call.

Hope this helps. Ken.

Terribly sorry old man..Im still stressing about dropping the Gorton Pantograph...

Gunner

"Anyone who cannot cope with firearms is not fully human. At best he is a tolerable subhuman who has learned to wear shoes, bathe and not make messes in the house." With appologies to RAH..

I removed the table tonight..and the screw is bent in two places, both of which should be easy to straighten. Unfortunately......the bends are on the wrong side of the nut, which is bolted to the top of the knee, under the table. And the screw will turn, but only to the first bend. Unfortunately again..it only will screw out in one direction, as there is a flange machined into one end of the screw, so the direction it comes out..is the one blocked by the bend.

The nut is held in with a couple of large screws, both directly under the screw. The screw has to come out to get to the nut fasteners..and it wont come out because of the bend...sigh. Now I have to figure out a way to straighten it while its still in the machine, though fully exposed. The nut is a long cast iron "tube" tapped inside for the thread

I suppose I could take a die grinder and cut away that flange that holds the screw from going the other direction..but it aint gonna be pretty....

This is gonna be a head scratcher..

125 thou per revolution, so its 8 TPI by 7/8", if anyone happens to have 4' of this kicking around...

Gunner

"Anyone who cannot cope with firearms is not fully human. At best he is a tolerable subhuman who has learned to wear shoes, bathe and not make messes in the house." With appologies to RAH..

Old gunsmith: "When I was younger I could straighten a barrel over my woody"

Young gunsmith: "He! I bet you can't do that any longer!"

Old gunsmith: "Naaa.. I'm not that strong anymore"

Gunner wrote in news: snipped-for-privacy@4ax.com:

Gunner, Try McMaster Carr, they care ACME screws in standard lengths/sizes, and are relatively inexpensive.

I might just have 4 feet of that stuff, Came off a large process camera, I'll let you know tomorrow

On Tue, 23 Sep 2003 06:16:21 GMT, Gunner pixelated:

If you can get to the outside of the bend, maybe a porta-power bow-and-arrow sling would do it. Wrap cable (bow string) around the ends of the screw (bow), secure, and insert the porta-power ram (arrow) in between, against the bend. Pump it straight. Use additional cables to maintain the integrity of the screw in the mid points if necessary.

---------------------------------------------------------- --== EAT RIGHT...KEEP FIT...DIE ANYWAY ==--

- Schnazzy Tees online

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Yes Jim, but the indicator shows the movement, which is the most important thing. ERS

You could try straighten the screw by heating the bend with an acetylene torch. If you heat it to cherry-red it will bend easily. Perhaps you = can straighten it by running it through the lead nut while it's still red?

Don't worry about ruining the hardening, the screw is probably soft = anyway

- besides, it's not a swiss clockwork we're dealing with here.

--=20

-JN-

MSC has them too, but they are rolled threads. I would think a fellow could cut an acme thread more accurately in any good lathe. I've made many of them of 12L14 at the Lumber mill I used to work in. Of course if the lead screw is worn out you get a sloppy lead thread in your screw. Cutting acme threads with a follow rest is a bit like juggling sometimes until one gets used to it.

Gunner,

The force that bent it was from the handle hitting the dirt, am I correct ?

Can you remove the handle and housing and put a long piece of pipe on it up almost to the nut?

Or if its on the other side of the nut, maybe use a pinch bar and an aluminum block, after rotating the bow towards the underside of the table..... Better yet, get a helper and do both.......

Im straightening aluminum extrusions in the vises, loaded on the cnc before machining, measuring warpage with an indicator in the spindle, Im using a

16in. crescent wrench and a piece of pipe to add leverage.........

The keyword here is "leverage"......

Good Luck.

Gunner, have you looked at the precision leadscrews from

My FiL used one to fix up his lathe - accurate and cheap. Geoff

So turn the screw 180 and drop it again?

;)

Joel. phx

I think this is my only option at the moment. The Nut is a hotdog shaped piece of cast iron, and will not take a lot of pressure, if I try to do a pipe and force straighting, and there is not too many places I can clamp it, to take the pressure off the nut. The screw is pretty darned soft btw.

Master Carr doesnt carry 8 tpi 7/8" acme screw..or its not listed in my yellow book..sigh..so Ill try the red heat thing with a rosebud, then back it through the nut, unless anyone thinks this is a "Bad Idea".

Anyone?

Gunner

"Anyone who cannot cope with firearms is not fully human. At best he is a tolerable subhuman who has learned to wear shoes, bathe and not make messes in the house." With appologies to RAH..

Yup. No 7/8 x 8 tpi listed. Darn it.

Respects

Gunner

"Anyone who cannot cope with firearms is not fully human. At best he is a tolerable subhuman who has learned to wear shoes, bathe and not make messes in the house." With appologies to RAH..

On Sat, 27 Sep 2003 09:19:42 GMT, Gunner pixelated:

Y'all can find a steel bar and a file, cain't ya? It'll be good practice.

-- Music washes away from the soul the dust of everyday life. ---- --Unknown

Dear All, I missed the first part of this posting ,so I dont know the size of the Lead screw. However 2 years ago I straightened a 3ft 3/4" screw on a Theil Miller. It was bent 100Thou eccentric but took less than 1/2 an hour to get within 0.5 thou of concentricity. The method was suggested by my friend Harold who called It a "Jim Crow". Take 2 pieces of angle iron I used 2"x2"x6" long ,on the first I welded a piece of 1/2" square bar on the 2nd at each end I welded a similar piece. Place the angle iron between the vice jaws. Mount leadscrew between centres on lathe. "clock maximum eccentricty, mark ,transfer to vice ,nip gradually,transfer to between centres,re-clock, transfer to vice-repeat ad nauseam and in about 1/2 hour good as new leadscrew! Kind Regards IanIn article , geoff merryweather writes