How to Clamp Compound Miters for Glue-up
Is there a clamp or glue-up method to fasten compound miter joints for a frame? No regular frame clamp will work.
—John H. Bolden, Dallas
You can try two possible clamping techniques for these awkward frame parts, John. To grip the angled shape of the molding, use the pinch clamps shown above. (Clamp-All starter set no. H3703, $36 from Grizzly Industrial, 800/523-4777 or grizzly.com.) Flip the frame parts upside down, add glue, and then use the clamp spreader to attach the clamps to the back side of the frame. This method has two disadvantages. The clamps leave small indentations on the back side that you'll need to putty before finishing the frame. Second, by working from the back side, it's more difficult to confirm that the pieces are aligned accurately.
Another option is to use stretchable tape to hold the pieces together. (Scotch Stretchy Tape, $6 with dispenser, 3M, ScotchBrand.com.) Again, with the pieces upside down, apply glue and stretch tape between the pieces, as shown above. Although you assemble the frame upside down with this method, too, it's easy to turn the assembly back over, as shown below, to check the joints without the risk of a clamp coming loose.