This is catching the MOAM's attention today….. a flat caul looks honest until you clamp both ends — then the middle bows up and your dado, scarf, or panel joint starves….. Today’s tip: make a cambered clamping caul so end clamps drive pressure where clamps can’t reach.
Why it matters: Fine Woodworking (Gary Rogowski) spells it out — ordinary flat stock bows when you load the ends; a slight crown (camber) flattens under those same clamps and pushes into the middle. Asa Christiana’s case work uses the same trick across shelf dadoes in case sides. On a Chamberlain Marblehead gunning dory, that same caul keeps scarf joints and laminated stems / keel stock flat while epoxy cures. One stick of fir, two clamps, even glue-line pressure.
Materials
- Ordinary fir construction lumber (less likely to mar hardwood than dense hardwood cauls)
- A 2×4, ripped roughly in half for caul stock
- Useful lengths about 16″ and 24″ for most cabinet / case work; cut longer for wide panels
- Optional: wax or packing tape on the caul face so glue doesn’t stick
Tools
- Tablesaw or bandsaw (rip the 2×4; cut to length)
- Handplane (blend the camber; knock off sharp corners)
- Bar or pipe clamps — one at each end of the caul
- Straightedge or dry-fit scrap to check pressure before glue
Steps
- Rip and cut stock. Rip a fir 2×4 roughly in half. Cut cauls about 16″ or 24″ long for typical case work; go longer when the panel or joint spans wider (Rogowski).
- Lay out the camber. Mark the midpoint as the high spot. From that center, taper each end down about ⅛″ to ¼″ — that drop at the ends is the camber (Rogowski).
- Plane the blend. Handplane a smooth crown from the high middle down to both ends. Knock off sharp corners that could dig into the work.
- Orient the face. Put the convex (high) face toward the workpiece. Flat or concave face down is the common miss — you’ll recreate the flat-caul bow problem.
- Clamp the ends only. Set clamps at both ends of the caul. As they close, the camber flattens and drives pressure into the middle — across a mid-case dado, a scarf glue-up, or a panel that needs to stay flat.
- Dry-fit, then glue. Test pressure on a dry joint first. Too much curve → plane the middle flatter. Not enough mid-span squeeze → increase the end taper a hair and try again (Rogowski). Then glue for real.
MOAM’s shop note: Biggest mistake is putting the flat face down — then you’re back to a bowing bar that lifts in the middle. Second mistake is over-cambering: a monster crown can dent soft stock or refuse to flatten before you over-clamp. Start in the ⅛″–¼″ end-drop range, dry-fit, and sneak up on it. Wax or tape the caul face so tomorrow’s cleanup isn’t chiseling fir off your case side.
MOAM Out.













