#WoodWednesday: The Secret to Foolproof Glue-ups

Here at Spring House Press we steer clear of politics, but–as any woodworker worth their salt already knows–to get things done, it takes a village. . . of clamps. For instance, to glue up this single panel of a guitar amp cabinet, I managed to squeeze 15 clamps into a space of 2 square feet. More ridiculous than that: To guarantee good results, I would have been in trouble with even one less. So are clamps the secret to good glue-ups? No, not really. It’s more about what you’re clamping. In this glue-up, for instance, only 3 clamps are used to close up the joints between the 5 separate boards that make up the panel. The rest are used to secure each of the 5 boards to 3 separate clamping cauls. The cauls are the real and often overlooked key to flat glue-ups.

A clamping caul is nothing more than a thick hardwood board jointed by machine or hand so that one wide edge is dead flat. When gluing up a tabletop or panel of any kind, simply place the cauls an inch or so in from the edge of the assembly and clamp the flattened faces of the boards to the caul. Then when the panel comes out of the clamps, the bottom edges of all five boards will be flush and flat. (It’s worth noting—in this assembly keeping the panel flat is imperative; I was able to find some beautiful tiger maple, but it was already thin and I needed to keep the assembly as flat as possible so that the final workpiece doesn’t turn out too thin after jointing and planing the assembled panel.)

Clamping cauls couldn’t be easier to make and are a critical part of any workshop. To make your own cauls, start with a stable hardwood like oak or beech. Mill them from at least 2” stock and and aim for at least 2” wide to ensure that they won’t bend under clamping pressure. A good set of four clamping cauls made from beech has lasted me about 12 years so far. Just lay on a coat of shellac when you make them, then wax them frequently to make sure glue doesn’t bond to the caul when they’re in use. Sure, it will require a few more clamps, but you’ll be amazed at how easy a good set of cauls make it to achieve flat assemblies.   —Matthew Teague

Originally posted on March 2, 2016