Interesting info on clamp pressures

[kscott]

On Finewoodworking I found this. It would never occur to me that quick grip clamps provide more pressure than K-body type clamps. This is totally counter-intuitive to me. Your thoughts?
Ken

[oakey]

great test
quote" using a bathroom scale "
say what !
might had better placed the clamps on ones finger and hollered ouch when the clamps got tight
I personally have never seen a quick clamp that would clamp better[ meaning more pressure] than my parallel clamps
call me skeptical

[WilliamHodge]

I didn't realize that people used quick grip clamps for laminating wood until I started reading the Woodworking subreddit on Reddit. This morning I saw pictures of someone edge gluing up a 60" table top with three quick grip clamps. I would use pipe clamps, one per foot with padding to spread the force, with an extra clamp on each end.

With light weight clamps it's hard to adjust the force to get every thing flat. The one problem with adequate force is that all the glue squeezes out if you don't let it sink in before putting the pieces together.

Seeing the foot pound ratings of the different clamps was interesting. Thanks for posting the link to the blog post.

William Hodge

[Steve N]

It is possible to over clamp, and starve your joint, Dry and dry = poor adhesion. I guess what I am left wondering is if you don't clamp to exactly the pressure they infer, what? A week later, 2 years later, 200 years later your joint suddenly falls apart? Probably a lot of people going to get worried about this. So far my experience is that proper stock prep, followed by an ample application of glue, is more important than being able to crush out XYZ pounds per sq/in. I've always squeezed until I see some glue escaping consistently across the joint, and quit. Never have had those fall apart joints. Gonna chalk this up to some guy making a living saying blah, blah, blah......

William makes a good point about using enough of the right kind of clamps. That is an experience thing to get perfect, but to know baby clamps on a 60" wide tabletop aren't going to get it done, and on a 12" x 12" cutting board you don't need 14 Bessey K bodies. That falls under common sense.

I think a little bit of me said, Noooooooooooo when they were talking about using a bathroom scale. Trying to come off like it was a scientific study, and their test equipment likely wasn't worth a darn.

[fredhargis]

I remember reading that article when it was published, and a few months later another reader challenged the resultws in a letter to the editor. FWW stated they were surprised by it as well (IIRC) but they also said the results are stated correctly. Coulda knocked me over with a feather.

[Curlycherry]

Horrible, terrible, lousy test. They used bathroom scales. Those use springs. Springs are wildly variable if not compressed EXACTLY the same in every compression, which by their very nature is impossible. They should have used load cells. I've got some at work that go up to the ranges needed. I should duplicate their results and show them flat out how terribly wrong they are. Cripes, they didn't even do their calculations right.

[kscott]

I would be interested in seeing results using better equipment. I simply cannot believe that the quickgrip provide more force than the parallels.
Ken

[K. L. McReynolds]

Look at the face area of each clamp. The quick clamps have a much smaller area for clamping pressure---thereby creating more psi.

The key to the best clamping success is to get equal pressure that does not starve the joint by pushing out too much glue.

The difficult part is that each species of wood(and even each piece of wood) has a different grain consistency which absorbs glue differently. Gluing red oak to hard maple means the oak allows more of the glue into the grain than does the maple. So, the normal pressure required to clamp two pieces of like species is either too great or too light.

Clamping end grain versus side/face grain requires different pressure. Miter joints often require different techniques and prressures.

On this forum, this subject has been hashed, rehashed, and overhashed. The usual result is that clamping pressure is what is necessary to make a long lasting stable joint. And that cannot necessarily be done scientifically in most of our shops.

[kscott]

On the site the pressure is given in pounds, not P.S.I. and that is what I am questioning. If you add a tiny caul to the parallel clamp you could increase the P.S.I. but that would not make them more effective as clamps.
Ken

[boblang]

When magazines publish stuff like this, it's a sign that they have run out of good material. Editors love to pretend they are scientists now and then, and most don't know what they are talking about, especially on this topic. Good fodder for generating BS discussions, but no nutritional value.