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Custom Clamping Cauls

Click on any picture to see a larger version.

Sometimes when doing a glue-up there is a small correctable problem that needs to be dealt with while clamping or you discover a place where no clamp can adequately reach. When that happens, a caul can come to the rescue. A caul simply spreads clamping force or redirects clamping force in a specific direction or area, and can be an extremely helpful "accessory" to your woodworking efforts.

Figure 7 - Note the small bow as indicated by the center of this workpiece being slightly off the work surface

When building the "Big, Big Maple Bookcase" project , the right hand side piece of the taller bookcase developed a very slight concave bow. It was not anything to particularly worry about, since it could be easily flattened with just a little pressure and with one finger, but when it came time to put that side piece into place, there was no way to push the middle of the board flat against the shelves while the glue dried. I would have needed 6-foot long deep-reach clamps, which I am sure someone makes, but I don't have. Frankly, even if I knew where to buy them, I was disinclined to make any additional purchases with the holidays rapidly draining my pocketbook. So the first thing I thought of was to make custom cauls. And it is so easy.

First I found a fairly straight piece of 2 X 4 dimensional lumber. I jointed one edge to get a nice straight starting point. Then I cut the 2 X 4 into four matching-length cauls. I clamped the four pieces together and created a slight camber so that the middle of each piece was slightly "wider" than the ends.

Figure 8 - I started making the cauls by jointing the edge of a fairly straight 2 X 4

Figure 9 - Then I cut the 2 X 4 to the lengths I wanted for 4 cauls

Using a hand plane (I like to use my Lie-Nielsen Jack Plane, but a jointer or even a smoothing plane will work), start about 4 inches from one end and take off a whisper. Move back an inch or so, and take another whisper. Keep going, each time moving back an inch or so and keep taking swipes all the way to the ends of the boards. When your last swipe starts at the middle of the board, turn the group of boards around and repeat the process on the other end. In minutes you will have uniform cauls, each with a slight taper towards the ends.

Figure 10 - With all 4 pieces locked in my bench vise, I planed a slight camber

Figure 11 - Finished cauls... with the centers touching you can see how the ends are slightly separated. This is the planed-in camber

With those cauls placed across the side, I was able to clamp the two ends of the cauls, tighten them, and the slight extra width in the middle of the caul assured that the slightly bowed side piece flattened out and my glue-up was a success.

The illustrations below (Figures 12 and 13) show how a caul, in theory, works. In this example there is no way of putting a clamp in the middle of the shelf side to pull the bowed section of the shelf side down tight to the shelf. The slightly cambered caul can be clamped on both ends and the "thicker" middle section will exert considerable pressure in the middle.

Figure 12 - No clamp I had would reach the middle of the 14-3/4" wide side piece, so...

Figure 13 - ...the answer was to make a caul that would span the width and then two clamps could pull the side piece down flat

Manufactured cauls are available if you are not interested in making your own. I saw the Bowclamp Clamping Cauls once while visiting Highland Woodworking, and they really are beautiful, versatile, and well made. They come in three different lengths or you can buy a set. But if you are ever "stuck" needing a clamping caul, remember, they are fairly easy to make.

Speaking of the Big Maple Bookshelves, the latest video is now available by CLICKING HERE . You can see my homemade clamping cauls in use as I glue up the larger of the bookcases and you can watch me grapple with a job that would have been so much easier with a helper… oh well! With all that work finished, there is some important detail work to do, so stay tuned. And next month in this column I plan to give you the "nickel tour" of my latest home improvement project.

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Steven Johnson is retired from an almost 30-year career selling medical equipment and supplies, and now enjoys improving his shop, his skills, and his designs on a full time basis (although he says home improvement projects and furniture building have been hobbies for most of his adult life). Steven can be reached directly via email at sjohnson@downtoearthwoodworking.com

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