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Swinden Vice Problem

Problem with main thread

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David Millar 328/01/2021 16:19:54
15 forum posts

Hi There,

I wonder if someone could give me some guidance.

I bought an old Swinden vice a few years ago from a car boot sale. At the time of buying I could appreciate the quality of the vice but hadn't heard of that brand before.

It was working fine after just a good clean and lube up.

I let work borrow it and now a section of the thread is very tight. Only over an inch or two but tight enough to make using it awkward.

I'm guessing that the main thread (I don't know the proper name for it) has been stretched by over zealous tightening and that's what is causing the problem.

Does that sound like a likely diagnosis?

Any ideas for a remedy? I've tried working the jaws back and forth over the tight section but it hasn't helped.

Could I run a tap down the thread to try to correct the stretch?

If that was a sensible option, does any one know what the thread is? I've had a snoop around the internet but no luck so far.

I can't complain too much about the damage occurring at work. It's my Company

David

not done it yet28/01/2021 16:39:02
6285 forum posts
20 photos

You will need a die, not a tap. A tap will alter the action for the whole length of the screw and may not help for that sticky section. Probably easier/cheaper to either skim the dodgy threads on the lathe if it is an awkward size thread or just make another.

David Millar 328/01/2021 16:42:04
15 forum posts

Thank you. That makes sense.

Howard Lewis28/01/2021 16:49:36
5241 forum posts
13 photos

What form is the thread?

It could be Whit form, (or 60 degree if the vice is of American origin ) or it could be Acme, Square or Buttress.

Thread gauges may all you to find the form and pitch

Then you need to measure the diameter and the pitch of the thread.

"Running a tap down the thread"

A Die actually, for the male thread.

This may cure the immediate problem, at the expense of removing metal so that some of the threads will be thinner than they should be, leading to increased backlash and reduced strength in that part of the thread..

Howard

David Millar 328/01/2021 17:17:44
15 forum posts

Thanks Howard. I guess I've got nothing to lose from trying to recut the thread. I'll give that a go.

Thanks to you both.

Jeff Dayman28/01/2021 17:23:17
2169 forum posts
45 photos

Before doing any machining rework, I'd suggest checking for dirt / grit jammed anywhere. it is very possible to stretch a vise thread, but grit stuck somewhere happens more often. The nut / screw may have a bunch stuck in it at one spot, or the slideways may.

David Millar 328/01/2021 17:57:28
15 forum posts

Thanks Jeff. I'll check that when I strip it down.

Pete Rimmer28/01/2021 18:41:06
1053 forum posts
69 photos

Sounds like they have stretched the thread but I've no idea how as they clamp so well it should not be necessary. Probably using it as a press.

They are pretty easy to dismantle. Strip it down and inspect the thread.

David Millar 328/01/2021 19:25:36
15 forum posts

Thanks all. That'll be a nice lockdown project

John Reese29/01/2021 01:52:11
975 forum posts

Lesson to be learned: do not lend your tools.

John Reese29/01/2021 19:18:46
975 forum posts

I would suggest making a new screw. The threads on either side of the stretched area will be out of phase. I hope you find a cause other than a stretched screw. I have owned quite a few vises over the years and I abused them. I never stretched a screw. I think it would be near impossible to stretch the screw without putting a cheater on the handle and that would likely bend the handle before the screw stretched.

David Millar 330/01/2021 08:33:34
15 forum posts

Thanks for that John. I'll have a close look as I strip it down. I hear what you say about, if it was stretched, the thread being out of phase beyond the streched area. That doesn't seem to be the case. The thread is tight over an inch or two, then runs freely again. Perhaps the thread profile has been damaged rather than stretched.

Food for thought!

Thanks to you all. I'll let you know how I get on.

David Millar 302/02/2021 19:25:56
15 forum posts

Hi all. Just to give you an update. I didn't have easy access to a die do I spent an hour dressing the problem area of the thread with a flat hand file and it seems to have done the trick. It's 99% as it should be. Runs freely apart from slight resistance over about 1/4".

I identified the problem area by screwing into the "captive nut" section until I felt resistance then backed the thread back out again to dress it then tried advancing it again.

I couldn't see much wrong with the thread but there must have been something!

Thanks again to you all! Much appreciated.

Jeff Dayman02/02/2021 19:28:36
2169 forum posts
45 photos

Glad you were successful! a good vise is a pleasure to use.

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