Question (WOODWEB Member) :
A technique for clamping flat panel glue-ups I use is to take four pieces of square tubing, 1" or larger. Stainless would be the best, but it can be done with black pipe. If black pipe, laminate one face with vinyl edge banding so that the glue does not react with the metal. Stack the tubing two high and drill corresponding holes through both pieces about 30" apart. I drilled to allow a 3/8" carriage bolt. Run a 4" carriage bolt through the hole, and lay out two pieces of tubing on the table with the bolts pointed up. Lay up as much panel, drawer front, table top, etc. in between the bolts as possible. Drop the top tubing over the bolts, and snug down with a wing nut. Clamp the panel together as tight as you want. With the panel sandwiched between the tubes, they cannot cup when pressure is applied by the clamps. Using 60" tubes, and regular pipe clamps I can lay up about 14 square foot of door panel at a time, and they will come out perfectly flat.
From contributor C:
We do something similar to this except that our cauls are spring loaded at both ends. One end pivots and the other is buckled with a destaco latch clamp. The cauls themselves, in our case, have a UHMW liner on the bottom to keep glue from sticking and iron from staining the wood.
Once all the boards are level and held in place, we then add clamps above the boards to balance the compression. These can be set above the glue lines also to prevent ferrous stains. The bumpers are waxed to help repel glue, but the clamped assembly is removed from the bumpers so they don't all set up. This makes for flat and true panels every time. Our glued for width stock is also planed after glue up at times, so then the stains are not a problem, but the use of bumpers (we have quite a collection) makes any glue up easier.