Clamping cauls: The secret to great glue-ups
Woodworkers spend a lot of time cutting accurate joinery. Yet even the most accurately cut joint won’t be perfect if you glue it together incorrectly. Not only must you put the right amount of glue in the right places, but you also need to do the same with the clamping pressure. Some joints, such as dovetails, need pressure only in isolated spots, while others, such as thin edge-banding, need even pressure over the whole area. The answer is not fancier clamps or specialized jigs; it is shopmade clamping cauls. Quick to make and easy to use, cauls not only pull a joint tight and keep it at the correct angle, but they also protect the workpiece from direct contact with the clamp jaws.
Flat tabletops start with clamping cauls
The simplest cauls are great for tabletop glue-ups. When edge-gluing boards to make a solid-wood panel, you can use hardwood cauls about 1 in. thick by 2 in. wide by up to 30 in. long. Use them in pairs to sandwich the boards together and keep them flush while other clamps apply the main pressure to the boards’ edges.
Some woodworkers recommend putting a slight convex curve on the clamping faces of the cauls. For this job, it may not be necessary. After all, no great force is being applied; you are only using the cauls to hold the boards flat, not bring them together. However, for panels wider than about 30 in., cauls are less effective. Splines, biscuits, or dowels will work better to align these boards, although they are more time-consuming.
To prevent the cauls from sticking to glue squeezeout, apply packing or duct tape to the contact faces. Elevate the boards off the bench and clamp the cauls in pairs, sandwiching the boards flush with each other.
Cover the cauls’ clamping surfaces with packing or duct tape to keep them from getting glued to the panel as squeeze-out oozes from the joints. Use a pair of cauls at each end of the panel, but if the panel is more than about 2 ft. long, use a third set of cauls in the center.
For the clamping cauls at either end, have the clamps come in from the ends of the panel to get even pressure across all the joints. For the center pair of cauls, the clamps have to come in from the edges of the panel.
Finally, apply the edge clamps to draw the boards together while the cauls keep the tabletop from bowing.
Clamp on the cauls and then apply the edge clamps. You don’t need cauls to protect the edges from these clamps because you will clean them up later. The greater force of the edge clamps will easily overcome friction from the cauls and bring the boards together.
This is an excerpt from issue #218. Read the full article here.
More from FineWoodworking.com:
- Convenient Cauls for Panel Glue-Ups
- Curve Calls Precisely for Even Pressure
- Video: Avoiding Glue Squeeze-Out
- Tips on Gluing Joints
- Video: No-Stress Glue-Up
Simple, shopmade clamping cauls are key to perfectly gluing up woodworking joints. Read how to use them for gluing up tabletops in this excerpt of a Hendrik Varju article from FWW #218
For more tips on using cauls, read Hendrik Varju’s article from FWW #218. In the article, he explains how to use them for gluing edge banding (pictured here), dado joints, dovetails, and through tenons.
For more tips on using cauls, read Hendrik Varju’s article from FWW #218. In the article, he explains how to use them for gluing edge banding, dado joints, dovetails (pictured here), and through tenons.