Cauls are indispensable in your woodworking shop for laminating panels, and they are both utilitarian and easy to make. They are not to be confused with the fatty omentum covering the intestines of a cow or pig or the amniotic sac that protects us in the womb. The caul we’re talking about is merely a piece of wood that plays an important role in glue-ups.
They are used when clamping a panel for glue-up, such as gluing two panels together to make a thicker single panel. Unless you have a very large collection of various clamps in your shop, it’s unlikely you will have a clamp that reaches into the center of the panels. They will be fine for the edges of the panels but not into the center of the panel surfaces.
This is where a caul comes in.
If your projects include doors, cabinets, or tabletops, the use of cauls is most often essential to a successful outcome. Any of the types of bar clamps will be fine for the perimeter of the glue-ups, but what about the center?
How Do You Keep a Glue-Up Flat?
With clamps around the edges, we know the glue-up will be strong. But, if the clamps don’t reach the center of the panel surface and no pressure is applied, the glue-up across the span will be weaker.
Using a caul or two, though, takes care of that for you. A piece of wood, perhaps a 2 x 4, or one ripped in half, that runs across the panel in several places, clamped tightly, will apply that pressure in the center of the panel surfaces where the clamps can’t reach, ensuring a tight glue-up. A tight glue-up gives you a flat surface.
How Do You Make Wooden Cauls?
It’s likely you have scraps of wood around your shop, and if you do, you can make some cauls pretty easily. Maybe a piece of oak or cherry from a previous project, or even pieces of a 2 x 4, are just sitting around. A 24” or even 36” length will do the trick, depending on the project. Let’s say it’s a tabletop, whether for the shop or your dining room, and you need to laminate two pieces to create a thicker piece for the top.
You’ll want to run the scrap piece through your joiner to create an even edge and then the planer to make two parallel surfaces. Take a further step to create a slightly convex surface – – it bows up – – in order to create greater pressure in the center of the surfaces of the panels being glued.
To do this, measure down 1/32” at each end of the piece, and use a plane to take down the end to that mark. This will create a high point in the center of the piece, the convex, or cambered, feature.
When you clamp one end of the now cambered caul to the panels being glued, the other end will be slightly raised because of the camber. But, when you clamp that second end to the panels, that convex feature applies pressure to the center of the panels. This will ensure an even and strong glue-up.
The camber is only 1/32”, a slight convex feature, and the pressure on the caul will not be so great that it will crack or split. But, it will add just that little bit of extra pressure in the center of the panels where clamps can’t reach.
Here’s a video that shows how to make a cambered caul and how to use one.
The task is easy and quick, and you likely have all you need in your home woodworking shop to make your own cambered cauls. As the fellow in the video says, it’s a ten-minute process.
They are easy to make, reusable, and cost nothing extra if you have wood scraps handy to make them. They will make a world of difference in making that door or tabletop, and you’ll end up using them often.