How much clearance should there be between the mating surfaces of a joint? Is .002″ enough? Is .010″ too much?
Tim Inman: Mating is the operative term. If you can see light through the edge of the joint, there is too much clearance.
John Brock: It’s more of a feel thing for me. I want the joint to be a clean, firm fit, with no wiggle or slop before glue-up. Remember, the glue is only there to hold the joint together. The strength comes from the mechanical fitting of the joint, and with most species you can count on a little compression in the wood to help out. On a mortise and tenon joint, I want to have to press the tenon into the mortise with a little pressure. If it falls in, it’s too loose. If I need a hammer to test a joint, it’s too tight.