How To Make Cauls?

This week’s question comes from Geoff. He writes:
I have a question about cauls and how to make them. I have made some small ones (about 24″) out of some 2x pine. They did the job of gluing up a small table top, but… I want to make a real “set” of them but I don’t know what to make them out of. Could I laminate 1/4″ ply (I have a lot of scrap!) over a curved form to create a slight camber or should they be made out of maple or another hardwood? Thanks for the help and keep up the great work!

And here was my response:

Here’s the great thing about cauls Geoff. They can be made out of just about anything. I have a little bucket that I keep behind my bench that is full of little scraps of wood of all shapes and sizes. But they are really just scraps. Nothing made specifically for that purpose. The only time I specifically make cauls is when there is a very special clamping situation. And usually I use them for that task and wind up losing them a few weeks later.

So I use everything from plywood to solid wood scraps of all species. If you are making a really nice set, you probably can’t go wrong with oak or maple. Poplar would be a fine choice too, as would plywood (if done correctly). If you make a cambered caul out of 1/4″ ply, like you mentioned, you’ll need quite a few strips before the sandwich is sufficiently resistant to bending. You want enough resistance so that the crown of the camber provides the appropriate amount of pressure. You might have more luck using solid wood, but the ply is certainly worth a shot.

** For those who don’t know, a cambered caul is simply a caul that has a curve in it. These are most useful when clamping long surfaces where you can’t get clamping pressure in the middle of the joint. The best example I can think of is clamping a bookshelf into a dado in the side of the case. The crown of the cambered caul goes on the center of the joint and the ends get clamped down. This applies the needed pressure all the way across the joint. The trick, is figuring out how much of a curve to put into the caul in the first place.

Related Links:
Previous Question on Curved Cauls
Fine Woodworking Article on Making Curved Cauls