Question about Parallel Clamps

[John Helles]

Hi,

Yesterday I bought some parallel clamps and when I got home I noticed that the fixed jaw was not square to the bar on several of the clamps. The distance from the top of the bar to the top of the fixed jaw is just under 4", and over that distance they are out of square typically by 1/64" - 1/32". A couple of 12" clamps were worse (1/16" - 3/32").

Previously I had thought the whole point of parallell clamps was that the two jaws were each square to the bar and parallel to each other.

Does anyone know what sort of tolerance is acceptable ? Have I bought junk that needs to be returned or am I missing something here?

Thanks for any replies.

[Brian Tymchak]

Hi John,

Did you take those measurements with something clamped in the jaws or without? They might square up under pressure. Just speculating here. I haven't actually checked the squareness of my Revos. And that misalignment may not make much difference in the end. Even if I'm using my Revos, I'm always going to check for square on my glueup using other means.

It would be interesting to know which direction they are out of alignment. If they are short at the tips of the jaws, they might align under pressure. If they are short at the bar, well, that may be a little different story.

[glenn bradley]

There are planet of 'parallel' jaw clamps out there of dubious quality. The jaw on the Irwin offerings are downright sloppy. The Peachtree and other 'discount' offerings all fall pretty short of the mark. Jorgensen Cabinet Masters and Jets seem quite good although they are bit heavy in longer length as are the Bessey Revo clamps. The older (and slightly lighter) Bessey K-body are my favorites but, of curse, no longer made. You are after jaws that are in line with the bar and sty parallel when under pressure.

P.s. Clamping pressure does not have to be super human. Distorting the bars by over clamping foils the parallel function. Ergo, poor clamps lose parallel under less pressure than better clamps.

[Judson Green]

I'll have a look at my k-bodys later but I don't think that fixed part is square to the bar. I believe the jaw is ment to be slightly acute so it will square up when in use.

[John Helles]

I took the measurements without anything being clamped (no pressure, just the fixed jaw). They are short at the tips of the jaws, longer at the bar side of the jaw, so the natural angle is a little less than 90 degrees.

[Judson Green]

Just got in from the shop.

277687

[John Helles]

Yup that looks familiar, though in my case its not hugely consistent from clamp to clamp. Thanks for showing.

[Brian Tymchak]

Curiosity got the best of me so I checked out a couple of my Revos this morning. As yours are, my Revos are a fraction short of 90* at rest, but deflect well beyond 90* under just moderate clamping pressure. The deflection beyond 90* at the near the tip of the jaws is right at 1/32". Now I don't normally clamp anything up right at the tips of the jaws so the deflection I show in these pictures is exaggerated beyond a typical use. But, interesting to know that those jaws deflect that much. Being plastic though, it seems reasonable and I'm not bothered by it. Here's a before and after of my experience:


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[Metod Alif]

Good quote from Einstein. He would (probably) understand various forces and their distribution in clamping situation, then use appropriate clamping technique. For some forms of mating surfaces, such as between rails and stiles, parallel jaws are not even adequate,
Best wishes,
Metod