Clamps open during use

[Mark Gibney]

I got four of these clamps at a yard sale. Problem is they open up when I use them.

I had one open up on a caul last week, however the passive arm was loose to begin with and I thought that was the problem (I subsequently had it spot welded). Various other clamps stayed shut tight.
332138
But two of the four open up on work I was routing last night.

They are a nice size, 13" jaws, make in W. Germany, so they "should" be decent, right?

Anyone know why this is happening, and how I can fix it?332137

[Tim Bridge]

The edges may be too smooth. Maybe file small notches along one edge so the movable section can grip the bar.

[peter gagliardi]

Check the edge of the movable jaw facing the fixed jaw, behind the spine it slides on for a set screw. Bessey clamps of that style have an adjustable setscrew in that location, you tighten it slightly as the clamp wears giving it more grip.

[larry senen]

without clutch plates (as found on smaller pony or pipe clamps) this type will loosen when there's any vibration. that's why i don't use them for holding fences or other machine parts.

[Mark Gibney]

You learn something new every day - I'll check for smoothness / set screw, and won't use then around any vibrating. Thanks everyone.

[glenn bradley]

Check the edge of the movable jaw facing the fixed jaw, behind the spine it slides on for a set screw. Bessey clamps of that style have an adjustable setscrew in that location, you tighten it slightly as the clamp wears giving it more grip.

Not to nit-pick but, the screw doesn't tighten anything. It simply rotates to a fresh set of threads for a renewed grip ;-)


without clutch plates (as found on smaller pony or pipe clamps) this type will loosen when there's any vibration. that's why i don't use them for holding fences or other machine parts.

I have not found this to be the case with quality clamps and reach for my clutch style clamps last. Just a difference of opinion/experience. Even Bessey "mighty-minis" at about $5 each hold tenaciously in their range of intended use. I use them by the dozen.

[pat warner]

A serious safety issue, especially if used during a hand or machine operation.
Not great for glue-clamping either.
Scrap the offending clamp; sooner or later it will land on your big toe.

[larry senen]

A serious safety issue, especially if used during a hand or machine operation.
Not great for glue-clamping either.
Scrap the offending clamp; sooner or later it will land on your big toe.

use them for all kinds of clamping with little problem. maybe any vibration is an overstatement, but why take the chance?
i

[peter gagliardi]

Not to nit-pick but, the screw doesn't tighten anything. It simply rotates to a fresh set of threads for a renewed grip ;-)



.

You're not nit-picking, but on mine, that screw doesnt do what you describe. It is bored and threaded at an angle to the spine, the threads have no value for grip, it relies on the clearance thru the jaw, allowing it to pinch opposing corners of the bar. The setscrew adjusts to allow the jaw to be adjusted closer to perpendicular to the bar so it will grip.
I can adjust them in until the movable jaw is fixed to the bar.