Lathe feedscrew problems

You need to know the diameter, the number of threads per inch if it's English, or the pitch of the threads if it's metric, and the thread form (probably Acme)

With that info, you can probably find a source for a section of ground thread Acme rod to fab a new leadscrew out of. McMaster Carr stocks some sizes, I think.

You may have to actually cut off the end of the old one, and graft the pieces together, in the event tha there are any fancy bits at the driven end. (No biggie. Can be done with the lathe while the leadscrew is off)

Cheers Trevor Jones

Don't part out a Maximat! Contact emco at

They quit the business of conventional lathes, but I know that they buy old Maximats, refurbish them and sell them. So they do have spares. And I bet they can and will help you.

Oh, did you check the shear-pin of the feedscrew?

HTH, Nick

Ooops, they did not.

Nick

================ What is the diameter and tpi of your lead screw?

If you get lucky, you may be able to use a piece of allthread, although you may need to get the ends machined at a shop with a bigger lathe.

Yes, allthread is not precession ground, but it will be a lot better than what you have, and unless you are doing very precision work any slight pitch inaccuracy won't matter.

A fallback position is to get a complete leadscrew machined at a commercial shop. On a big lathe, between centers, and a follow rest, this should be a piece of cake. Again it won't be to the millionths, but more than likely good enough. Even a left hand should not be a problem. Be reminded that there is a DIN/ISO trapezoidal thread that has a 30 degree included angle which can be difficult to tell from a 29 degree acme. For a one off, a M2 HSS bit will be adequate. There may be an extra charge to make one on a surface grinder. [1 hour max.] If you do get one made, use good material [4140?] and not generic HR/CR.

If there is anthing "fancy" [e.g. splines] on the drive end, you can cut this off and drill ream for a hole, do the same thing on the "new" lead screw, and epoxy/loctite a dowel pin in both parts.

Should be at least as good as new, maybe even better.

If the half-nut is "buggered" look into building it up with one of the epoxy/teflon compounds such as moglice, or if you are into the old world craftsmanship thing, you can try babbiting it. (See Lindsay books for info on this.)

Unka' George (George McDuffee) .............................. Only in Britain could it be thought a defect to be "too clever by half." The probability is that too many people are too stupid by three-quarters.

John Major (b. 1943), British Conservative politician, prime minister. Quoted in: Observer (London, 7 July 1991).

If all else fails. Remove the leadscrew and remachine or make an adapter to enable it to be reinstalled reversed end for end. This consigns the worn section to the rarely used tailstock end.

Jim

Yes, and the feed would now be engaging on the "other", unused, side of the thread for the full length. Randy

Thanks for all the good suggestions.

I emailed one supplier of custom Acme threaded rods to see if they can supply two 6' lenghts and also emailed the US rep for EMCO. I don't know why I didn't think to check with EMCO first!

The lathe feedscrew is totally a non-standard item. It is a 15mm rod with 16 tpi threads. The driven end is stepped down in diameter for a plastic/fiber thrust washer and the pot metal drive gear hub that is pinned with the shear pin. The back end is stepped down to 8mm for a length of 57mm. with a keyway and thread for the handle to turn the leadscrew when it is used to move the apron for milling operations.

I am sure I could make a copy of the thing if I can find a metric sized shaft with inch sized Acme threads.

Will keep you informed of progress. I really like the lathe and don't want to have to stop using it.

Paul

Jim wrote:

================ It should be a piece of cake for a larger machine shop to turn some cold rolled or 4140 to 15 m/m and thread to 16 TPI. Even if the thread form is non-standard, a good machinist should be able to grind a HSS tool to fit. They will require a steady rest, and I would suggest between centers. Enco can supply 15 mm drill rod and a 15 mm 5C collet (or use a 4 jaw and indicator to center for centers.) see

?PARTPG=INSRAR2&PMAKA=230-4215&PMPXNO=946241

15 mm should go thorough your spindle so you can machine the ends as required, and if you remove the tail stock you should be able to turn down, cross drill and mill the key way.

Most likely will be better than the original lead screw.

Unka' George (George McDuffee) .............................. Only in Britain could it be thought a defect to be "too clever by half." The probability is that too many people are too stupid by three-quarters.

John Major (b. 1943), British Conservative politician, prime minister. Quoted in: Observer (London, 7 July 1991).

4142 cold finished prehard stress relieved.

Why don't you buy a 9/16 or larger x16 tpi leadscrew and have it ground down (maybe centerless or center) the 15mm size.

Martin

Mart> Thanks for all the good suggestions.