Picture-Frame Clamps Hold Dovetail Parts for Marking
Holding boards in alignment while marking dovetails can be a challenge. Whether you mark with a pencil or a knife, any movement during marking will ruin your work. I solved the problem by using two 90° picture-frame clamps.
Place one on each side of the joint, adjusting the workpieces until they are in perfect registration. Tighten the clamps and mark the pins from the tails (or vice versa). The clamps hold the work firmly and will allow precise adjustments for perfect registration. With proper support, you can even use this method to hold and mark large casework.
Drawing by Jim Richey