Straighten a acme lead screw?



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

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wrote:

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.
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I might just have 4 feet of that stuff, Came off a large process camera, I'll let you know tomorrow
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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.
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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. <g> --
-JN-
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wrote:

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..
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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.
--
SVL



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Gunner, have you looked at the precision leadscrews from http://www.mcmaster.com? My FiL used one to fix up his lathe - accurate and cheap. Geoff
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On 24 Sep 2003 04:26:06 -0500, geoff merryweather

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..
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pixelated:

Y'all can find a steel bar and a file, cain't ya? It'll be good practice. <gd&r>
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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 <afn2nvg7s4m0ldkni48gk7mobqee2ur
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ian R. Weeks

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?
So turn the screw 180 and drop it again?
;)
Joel. phx

up
before
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Gunner,
Whats the dia and pitch ?
I got a nice piece of brand new saginaw 1.00 dia kicking around here somewhere.....
A 6 ft length, it would be either 4 or 5 tpi-----I paid a purty penny for it many years ago, for a project that was later abandoned......
--

SVL



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On Mon, 22 Sep 2003 10:59:07 -0700, "PrecisionMachinisT"

Ill check

Im pretty sure its only around 5/8 or .75 max. Ill pull it today. I think your screw is gonna be a bit big, but thanks anyways.
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..
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Gunner wrote:

The trouble with bending a screw is that you'll often deform the thread shapes. If the bend is in a threaded area, then just putting the whole thing back on a single centerline might not make it workable. This might be a replacement job.
KG
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Sounds like a job for a lead hammer with a soft 2x4 underneath for padding. Gary Brady Austin, TX
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padding.
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.
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wrote:

Greetings Gunner, I have straightened lots of shafts. And got 'em really straight. This is what worked for me. Saw vee blocks out of aluminum. The shaft rests on these in a hydraulic press. Beneath the shaft mount a 1 inch travel indicator. Rotate the shaft to find the high spot and use an aluminum pusher between the ram and the shaft. When doing threaded shafts I used a wide indicator point that bridged the crests of the threads so that the indicator didn't need to be moved constantly to find the high spot. Start to apply pressure and note where the indicator is. Relieve pressure and see how much bend was taken out. By applying more and more pressure and noting how much indicator travel equals how much bend removed you can guess how much firther you will need to go. Since the aluminum crushes with pressure you need to rotate the shaft each time when it gets close to straight to guage how straight it is. When the shaft starts to yield a little it will take less movement to get the same amount of straightening than when first starting out. When the shaft gets close to straight it will be very easy to over bend. If this happens it will take much less pressure the opposite way to put the bend back in. To get the shaft really straight you will need to move it in .001 increments. With a manual hydraulic press I have used a long bar on the pump so it is easy to depress and so a large movement of the handle translates into minute movements of the ram. You know my number so feel free to call if you want more help. Cheers, Eric R Snow, E T Precision Machine
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Very Good information.
Regards,
Stan-

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wrote:

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