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vice thread efficiency

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gerry madden12/01/2020 18:41:49
80 forum posts
38 photos

Hi All,

I'm just calculating the clamping force I can get using my large but ancient vice. Its mechanical advantage comes out at around 260 which would give some theoretically big forces but there must be some losses. Does anyone here have an experienced-based suggestions as to what this might be ? 10%, 50% 80% ?

Vidar12/01/2020 18:56:14
55 forum posts

If it is a vice screw it can't be very efficient as that would not work for a vice. If it was more than about 50% efficient it would just backdrive instead of keeping something clamped.

So less than 50%, and probably not even close to that as vice manufactureres likely wanted to be able to work up pressure and keep things stuck.

Andrew Johnston12/01/2020 19:27:26
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5111 forum posts
594 photos

The manufacturers data for my machine vice shows that the clamping force (lbs) is very roughly 90 times the torque (ft-lbs).

Andrew

gerry madden12/01/2020 19:56:26
80 forum posts
38 photos

Thanks all. Vidar you put me on the right lines and got me thinking. I found lots of data for screwjacks and it comes down to lead angle of the thread and CoF at the thread. So in my case its going to be about 20%. And when plug this figure in I end up in Andrews ball-park ! Clever stuff, maths

Gerry

not done it yet12/01/2020 19:57:46
3933 forum posts
15 photos

Look up ‘fireball tool’ for videos on testing vises. I expect there are others, too. Then work backwards.....

Nick Hulme12/01/2020 23:05:33
723 forum posts
37 photos

Your choice of friction modifier can make a difference.

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