adjustable length clamp idea

I'm buying these clamps from Doug. Doug says they need a full 1" thick material to go between the steel bits. I was thinking to laminate some spare 1/2" ply for this purpose. I would have had to make several lengths of these laminations to have different length clamps for the heads though.

Then I got to thinking that I could make a bunch of foot long strips of the plywood, cut one in half and then glue them up so that they are each 6" offset except for two using the 6" pieces glued flush to a 12" piece. Then I could go to TSC and buy a big handful of bolts and nuts of the same diameter as the clamp pins and have an adjustable clamping system. Easier to store and I could easily make them any length I needed without too much extra overhang. Maybe I should use 18" long pieces with 9" offset - make it easier to squeeze in two bolts per mated pair. If I need just a little more capacity but not so much as an extra middle piece would give I could have some of the pieces not line up flush with each other when bolted together.

What do you people here think of this idea?

Looks like good clamps and if I had some I would use them but my Collection includes Pipe Clamps, As my son is an Electrician and does a good deal of industrial wiring , he brings me several lengths of 3/4" EMT pipe which is excellant for clamps. I keep some long pipes standing in the corner waiting for their need, while most are mounte in the 2' to 4' range, for regular use.

When the time comes for long service I simply switch out the clamp bodies to the long pipes.

I think it's worth a try but I'd try it on some scrap first before you sink money into the plan. The bars that I had made up were oak and at least on the longer ones I was able to see a bit of bar flex if I really cranked them tight. I dont know if you'd get the same effect better/worse/no-different with shorter pieces strung together or not or even full length ones made from laminated ply. With shorter bars I never noticed any flex. I think I had made up a few pieces each of 3', 5', and 7' out of the oak and swapped the heads to whichever set I needed. I got rid of all the wood bars already so I cant check this, but I think the hole spacing I used was around 3" or so? Check the screw travel on them when you get them and just make sure you go at least less than the max travel.

Doug - I have a free offcut leftover from my folks home addition work I am going to use for this idea. I'll give it a whirl when the clamps arive and let you all know the results.

I think your going to end up with a banana shape when you apply the pressure. I watch 3/4" black iron bow under pressure of pipe clamps and that is the same basic design so you can most likely apply just as much pressure.

With all the joints your going to have problems even if you can make some really tight joints. Even if you do your still going to have to deal with clearances in bolt holes, the compressibility of the ply, the elongation of the bolt holes, etc. I will be amazed if you don't end up with banana shape when you tighten it up.

Laminating up some plywood bars might work, but joints are just asking for trouble IMO. I hope you prove me wrong though.

I'm now trying to better understand the physics of clamping. Is the torsion concern due to the clamps in question having fixed, immovable jaws? Would the possible torsion / lack of rigidity of the clamp bar not be a concern if the clamp jaw faces were attached by a swivel mechanism, thus allowing for a flat angle of attack onto the clamped object even with some clamp bar deformation?

Your going to see the bar bow upward towards what ever your clamping. It happens with any clamp to some extent. I use a lot of F clamps, I have seen the bar deflect 3/8" or more on 36" clamp and they have swivel caps on the screws. It's just the force trying to bend and stretch that bar. I have seen it on pipe too, just not nearly as bad.

The more rigid the less it bows. But with any joint your going to have some play and the more joints, the more play, the more the bow. And with those clamps it isn't gong to take much to hit the part your clamping.