Strap-type web clamps are a handy way to close the four corners of a box during glueups. A caul at each corner can help direct the clamping pressure even better without smearing the glue. I make mine from thick-walled, 2″-diameter PVC pipe.
I first rip-cut pieces of pipe on the table saw to remove about a 35 percent section of their circumference. After sanding the cut edges smooth, I cover them with 3/8″ vinyl tubing, slitted lengthwise to slip over the pipe edges. The combination makes sturdy, nonstick cauls that stand up well under clamping pressure.
– Serge Duclos