Q:

Your article “Surviving Glue-Ups” explained how curved cauls can be used to apply pressure where clamps can’t reach. But you didn’t say much about how to make the cauls. Is there a rule of thumb for the amount of curvature per foot of caul? Does the curve have to be symmetrical? What woods are suitable?

F.H. Lott, Minneapolis, MN

A:

You don’t have to be very scientific to make useful curved cauls. Just be sure they’re long enough for most of your glue-ups.

I use ordinary fir con­struction lumber for my curved cauls. It is inexpensive and less likely to mar hardwood workpieces. I have some cauls that are 16 in. long and some that are 24 in. long, which takes care of most of the cabinet work I do. I’ve found that tapering the cauls by 1/8 in. to 1/4 in. at their ends gives plenty of curvature, but don’t be afraid to experiment.

Frankly, I spend more time thinking about the national debt than I do about making the curves symmetrical. To make a caul, I cut tapers into the fir starting from the center. Then I blend in the high point with a handplane.

Try the cauls when you dry-fit a piece. If they seem to have too much curve to them, plane the middle of the caul to flatten it a bit more. If they don’t press down enough, increase the taper.

		Making curved cauls Use 2×4 fir construction lumber about 24 in. long, depending on the size of the case. Rip the stock approximately in half, then taper each end from the center about 1/8 in. to 1/4 in. A handplane softens the midpoint to equalize the clamping strength and to knock off a corner that could mar the workpiece.
		Curved cauls clamp across wide cases. Getting a clamp to actively apply pressure in the center of a case can be impossible. With a curved caul, pressure can be applied from the ends to the center.

Gary Rogowski is a contributing editor.

Drawing: Vince Babak; photo: Asa Christiana

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