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Shop-made Cauls by P. Michael Henderson

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Cauls are found in almost every experienced woodworker's shop. They were used by our woodworking ancestors hundreds of years ago, and maybe even thousands of years ago. They're so common that when we talk about woodworking techniques we usually forget to mention cauls - they're just there, like the air we breath. But for new woodworkers, cauls can be a mystery - "What are they used for?" and then, "How are they made?

Let me first give a short discussion about the use of cauls so you'll know where we're going when we start making them. Cauls are used when clamping a panel or a project for glue up. They provide pressure in places beyond the reach of standard clamps, or reduce the number of clamps required.

 

For example, in the picture below, I'm using some special cauls to make sure the sides of this cabinet are straight.  I put glue in the groove that the back fits into and I wanted to make sure the sides were not bulging outward.

A more common use of cauls is during a panel glue up - the cauls are used to keep the boards aligned during glue up.

In this glue up, six cauls are used to keep the boards of the panel aligned. The cauls also keep the panel flat during glue up and minimize the amount of work (and lost wood) to get it flat later.

I'll demonstrate the use of cauls in a panel glue up later, but now, let's talk about how to make the cauls.

The first issue is the material the cauls are made from. You can use almost any kind of wood, but many people use a good grade of construction lumber. Here, I'm using eight foot 2 by 4's.  The reason for selecting 2 by 4's is cost.

The ones I show here were less than $3 each. When you go to select your 2 by 4's for cauls, don't buy the cheap 2 by 4's. Good ones are not expensive, you don't need a lot of them, and you'll have them for many years.

Go to the stack marked "premium" (or some name like that) 2 by 4's. Those will probably be dry (most cheap 2 by 4's are "green" and still have a lot of water in them). If you select those, you'll have to let them dry out before using them - which could take a year and they might warp in the process.

In selecting your 2 by 4's, try to find those with the minimum of knots, or at least only small knots. Also look for straight grain. Examine the end to make sure this 2 by 4 didn't come from the center of the tree (you'll see the grain in a circle around the center pith of the tree). Premium 2 by 4's sometimes have the end grain sealed with wax.

As Martha Stewart would say, "That's a good thing." Make sure there's no splits in the end of the boards.


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