Acme Threads

[uncledj]

  Weird one.

  I've a very heavy, very large old Columbia vise that I've come across.  At OSU, one of their shops was throwing out this old Columbia vise because the threads on the ?nut? were stripped.   I've found that they're ACME threads and as I measure the diameter of the rod I get 1 1/8" diameter and count 4 threads per inch.

  I can repair this by finding a coupling nut that will thread onto the rod, cut off the part that's stripped and weld a coupling nut in it's place.

  The problem is that I only find 1 1/4" or 1" nuts offered with the 4 threads per inch.

  1 1/8" nuts are available in 5 threads per inch only.

  I wonder if this is actually a 1 1/4 rod that I'm looking at.   I haven't taken a micrometer to it, but as it sits it clearly measures 1 1/8" and it sure looks like 4 TPI.

  I'm measuring at the end and the threads don't appear worn at this point on the rod.

  Should I expect this rod that measures 1 1/8" is sized small to accommodate the loose fit desired for a vise?

[RDawson]

Got a good machine shop close by? With the industry here our local machine shop has worked with a lot of acme threaded stuff. Somebody like that might can help you. 

[M61A1MECH]

Looking at what McMaster-Carr offers and poking around on some machinist websites I find ,  you are correct that 1/4" or 1" ACME are typically made with 4 threads per inch and 1 1/8" ACME are typically made with 5 threads per inch.

I agree with Ronnie, search out a local machinist to verify what you have, It is possible the vice manufacturer made their own proprietary thread form, that is not really an uncommon practice.

The other possibility is maybe it is not a true ACME thread form, could a Buttress thread or a square thread, they look similar to ACME and are similar in strength and would be suitable for the lead screw on a vice. Again a half decent machinist would be able to tell you.

[Woody]

John do have some pictures of this project?