Source for 1/2-8 LH Precision Acme Lead Screw

I need a source for 1/2-8 LH Precision Acme Lead Screw for the cross slide of my Sheldon Lathe. The specs are listed below for the screw. I have a .125" direct reading dial. I think it is a single start screw but am not sure.

MSC has double start 1/2-8 LH, but what is the difference in single and double start?

Here are the specs on the screw from someone I know who worked for Sheldon:

The thread is an American Standard 29 degree Acme GP thread, 1/2"-8 left-hand. The screws made by Sheldon had a 5 degree 25' helix & measured .550" to .552" over 3.072" wires. They were made of Stress-proof 1/2" ground & polished stock.

Any suggestions greatly appreciated.

Thanks, Steve

Reply to
Sierevello
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Hmm ... by "direct reading", do you mean that the cross-slide moves 0.125" for a full turn, or that it moves 0.0645" per turn, resulting in a removal of 0.125" diameter from the workpiece?

If the dial is 0.125" for one turn, it should be single start. you would have a full turn adding up to 0.250" or 0.500" for a double-start 8TPI, depending on which measurement system you are dealing with.

A double start has *two* thread grooves. In this case, they would each have a pitch of 4 TPI, and one would run half-way between the turns of the other. As a result, it moves twice as far for a given rotation.

*And* -- your dial would have to be 0.250"

Hmm -- wasn't that "three 0.072" wires", not "3.072" wires"?

Can you still get the leadscrew from Sheldon? It is likely to have parts which are larger in diameter than the thread (let alone than the thread root), which would have to be turned to act as bearings, and to mount the gear for the power cross-feed, so starting with a bare threaded shaft would mean that you would have to join it to other pieces of metal to complete the leadscrew assembly. I know that my cross-feed leadscrew goes to above the 0.500" diameter at several points past the thread.

Hopefully, someone else will know where to get the pre-threaded stock. I'm afraid that I don't.

Of course, you could try turning a new leadscrew shaft yourself. They've told you the material and the starting size, and how to measure that you have the thread depth correct. You'll have to take out the old leadscrew and make a lot of careful measurements and a good drawing before putting it back in while you turn the new leadscrew.

You'll need a steady rest to support the rod as you turn the threads, or the threads will be too tight in the middle of the screw's length, thanks to it bowing while you turn.

Enjoy, DoN.

Reply to
DoN. Nichols

Green Bay manufacturing makes precision acme screws for machinery. Their link is:

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Reply to
Dick

Yep, what DoN said, all except for the steady rest. I can't help but believe he's really talking about a follower rest. A steady wouldn't provide the support you need, and would get in the way.

Nice post, DoN. It's important for readers to understand the difference between pitch and lead where threads are concerned.

Harold

Harold

Reply to
Harold and Susan Vordos

Steve, FWIW, good friend and sometimes RCM contributor, Gary Repesh, recently made a nice lead screw on his lathe. He used un-treated drill rod; machined it with a follower rest on a 14" Logan.

Reply to
Robert Swinney

Yes, you are right, a follower rest, which I have seen referred to as a "traveling steady rest" by UK posters, hence my mistake in terminology.

Thanks, DoN.

Reply to
DoN. Nichols

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