Strengthen Miter Joints with SplinesAdditional reinforcement will bolster the integrity of your piece.
I like the technique Marc Adams uses to cut accurate miters on a crosscut sled (“How to Cut Precise Joints on the Tablesaw,” FWW #235), but I noticed that there was no key or spline in the miter to reinforce the joint. Is there a biscuit hidden in the joint, or does he think it unnecessary to add strength with a biscuit or spline?
Thomas Hall, Greeley, CO
Flat, or frame, miters like the one shown in the article almost always need additional reinforcement to keep them together over the long term. Biscuits work OK, but my favorite technique is to assemble the mitered frame and then glue visible splines in the corners afterward. To do that, you must cut a slot in each corner after the frame is glued together. To cut the slots, I make a cradle jig from MDF that holds the frame at 45°. The jig rides against the rip fence and guides the frame through the blade.
Glue five layers of MDF together, joint the bottom flat and straight, and then cut through the block at 45° on the miter saw. Then just reverse the pieces to create the two ramps, and glue them to a base and side plate to create a square, solid jig.