How to Wood Glue a 45° Angle
by Damien Andrews
I could simply say go to an upscale woodworker's store and purchase a corner clamp or two. But that would make this a very short (and for the most part useless) article. Good corner clamps that will hold together the likes of a brace of 4" x 4"s or a couple 2" x 6"s are pretty pricey, and very specialized. Most do-it-yourselfers don't have call for such tools on a regular basis. And unlike a shop that frames pictures, the average do-it-yourselfer has no idea what size corner clamp he might need – when the highly infrequent need arises.
The following methodology will work no matter what size lumber you are gluing together at 45°. It will work just as well with 6" x 8" posts as it will with ¼" plywood. So that this article does not leave the impression that this process is only valid on one size of lumber, measurements will be omitted. Only angles and positions will be discussed. Ergo, in Diagram 1, the sizes of boards A, B and C are optional – fill in whatever sizes you're working with.
Start by laying out boards A, B and C in the approximate position of finishing on a flat surface (see Diagram 1) on a piece of plastic. Slip a plastic sheet between board C and boards A and B. If you don't want clamp dings in your wood (A and B), get pieces of the proper size wood to put between the clamps and the edges and insert them now.
Slightly tighten the clamp holding board B to board C. The inside of the 45° angle of board B should be at the corner of your jig, C. Tighten that clamp just a bit more now. Now, very lightly tighten the clamp holding board A to C. Tap board A as necessary to get it to perfectly meet board B. If necessary, loosen the clamp holding board B and make adjustments. When the two 45° edges are perfectly aligned, fully tighten the clamp holding C to B, and only slightly tighten the clamp holding A to C.
Gently tap board A away from the corner to open a tiny slit for glue. Use the tip of your wood glue bottle to generously inject glue into the slit. When you're satisfied that adequate wood glue has been injected between the boards, tap board A back into the finished position with board B. Fully tighten all clamps! Check your work using a square on the outside of the new 45° corner – if necessary, loosen the clamps very slightly and tap to make adjustments.
You can now add brads, nails, tacks or staples in the 45° angle as you deem fitting. NOTE: if you are going to be nailing, be sure to completely stabilize the freshly glued 45° angle so that repeated hammer blows don't misalign your work. Using a small drill bit to create a starter hole for the nails will also reduce the risk of causing misalignment.
NOTES: You can basically duplicate this process for installing various 45° holding systems, such as metal gussets and scotch fasteners. You can also use the system to simply hold the boards at the perfect 45° so you can screw or nail them together, without glue.
Be sure to use a board for the jig (C) that is of adequate proportion to the two pieces of lumber you've cut at 45°. In other words, don't use a 3/8" thick piece of plywood as the jig for two 4" x 4"s – use a 2" x 4", and so forth.