Vice feed screw and nut replacement

[MozamPete]

I'm looking at repairing an old machine vice that came with my mill when I brought it. I don't really have a need for it but figure I might as well tidy it up.

Once dismantled the dove tail, gib, jaws, etc all look in reasonable order, but the feed screw and nut (not sure it that is the correct term for a vice but you know what I mean) are stripped and need to be replaced. It's is about a 1/2 inch, 10 TPI acme thread.

While I could have a go at single point threading a new feed screw I don't think turning an internal thread on a nut that small would be an option. So I need to source an acme tap or a nut and some screw rod which I think will be problematic where I am (still need to check but I imagine it will be a internationally order off ebay - and with the current postal strike is South Africa who know how long it will take to get here)

The alternative is to just use a M12 thread - I have threaded rod and the necessary taps and dies for that. I know a 'V' thread is not recommended for a drive screw but what I would like to know is just how bad would it be. Would it work or is it a total no-no?

 

[John Hasler]

The V thread will work but it will take roughly twice the torque to get the same amount of clamping force as you would get with acme. Polishing and greasing the threads will help.

 

[MozamPete]

Found a supply of expensive ACME threaded rod - would of probably cost me twice what the vice was worth just for the rod and nut. Then I had a brainwave - went to the local car wreakers and picked up a car jack which had hardly been used for under a tenth of the cost. Has about twice the length that I need of a square thread rod and a extra long nut I should be able to adapt nicely.

 

[Walsheng]

Found a supply of expensive ACME threaded rod - would of probably cost me twice what the vice was worth just for the rod and nut. Then I had a brainwave - went to the local car wreakers and picked up a car jack which had hardly been used for under a tenth of the cost. Has about twice the length that I need of a square thread rod and a extra long nut I should be able to adapt nicely.

That is brilliant! Post some pictures.

John

 

[Rbeckett]

I think that idea will work great. And the machined place where the jack wrench goes will make opening, closing, and tightening much easier and better than the single point rod idea.

Bob

 

[george wilson]

Good thinking!! I rather enjoy making square thread screws and Acmes. The square thread is more of a challenge since the cutting tool width is critical. This is why they went to Acme. It is easier to do.

 

[MozamPete]

One small Hic-up. Had to go back and buy a second jack - this time one with a right hand thread. Should of paid more attention when I got the first one I suppose. Well at least I now have a length of left hand square thread on hand if I ever need it

Original stripped feed rod and nut from the vice:


First jack (with a left had square thread):

Second jack I brought, this time with a right hand thread:


Component roughly laid out just as is (still need to machine the feed nut to fit the vice, cut the rod to length, etc). The thread is not a typical square thread - it's doesn't look symmetrical, the 'valleys' seem wider than the 'teeth' and the 'teeth' seem to have a radius on the top. Any how, as it was in a jack it must been some sort of 'drive' thread so should work better than just using a bit of M12 threaded rod.




The jack also came with a small thrust bearing at the drive end so I think I will use it and bore out the cast end plate of the vice and to recess it in. May also need to add a spacer in between the end plate and the nut I'm intending to weld on to the end of the shaft as the drive to make sure the nut is still sticking out past the the vice base when clamping thin items.

 

[bollie7]

Its probably a rolled thread rather than machine cut. Thats good as it will be stronger than a cut one. Seems a shame to destroy a good jack but I've done the same sort of thing before so know where you are at. I picked up a scissor jack from a curbside cleanup recently. It came from a Ford Courior ute (Pick Up for the rest of the world. The Courior Ute that was sold here in Australia was actually made by Mazda I believe) Anyway this particular jack has a gear reduction drive on the end and the thread is larger in dia than a passenger car jack. So if any one is looking for a jack to use the threaded bar then keep an eye out for a jack from a commercial vehicle.
regards
bollie7

 

[MozamPete]

Components have been remanufactured. I decided to insert the thrust bearing in the spacer and just machine a light cut off the cast iron end plate to flatten it up - leaving the original parts as original as possible and in case something doesn't work.

Still want to knurl the space to give it some grip so I can use it to manually open and close the vice - but are waiting for my kurling tool to arrive.


Also installed a small Delrin bush in the end plate just to keep the threaded rod centralised and made a collar with a grub screw to fit on the inside to pull the vice open (the original just has a cerclip but the collar gave me more flexibility on the position instead of cutting a cerclip groove and then having a dimension wrong)


And a new coat of paint for the body.

 

[rick9345]

Nice Job
Way to repurpose