Thoughts on Mitered Corners

I've been thinking about ways to join wood at 90 degree angles. This is in part because I'm starting to think about making storm windows for the basement, and in part because there are picture frames in my near future. So I spent part of this week contemplating joints that have a miter on the show face.

Of course, the simplest way to do this is with a straight miter:

The matched angles of a miter provide some resistance to separation, but the primary benefit lies in the concealment of all the end grain. This is aesthetically pleasing, and can be advantageous in joints that need to endure weather, but nothing can change the fact that end grain to end grain provides a weak glue joint. So even with modern glues I always nail through with wire brads when making a frame.

Another way to strengthen the joint is to add some long grain to long grain contact. We can do this with a mitered half lap:

This has the added advantage of having more edge contact between the boards. You can also put a blind peg in from the back to keep these mated pieces snug. This does reveal some end grain on one side, but provides a much stronger joint. Although this joint looks simple enough, it can be hard to wrap your mind around the geometry: notice that one piece requires two cuts, but the other requires three. When I was drawing this, I kept trying to "cut" the wrong part of the the mating board, so before making any cuts I double check my layout.

You can take the long grain to long grain theme to another level with a mitered bridle joint. This joint starts to get complex.

Even with the increased complexity in the joint, this one is somewhat easier to understand in layout: each piece has one angled joint and one square joint, where the half lap has a more asymmetric structure, with one angled joint on on piece and both an angle and a square on the other.

While I was thinking on variants, I came up with the idea of adding a mechanical joint to the glue joint. I've never seen this done, but it must have been, and it seems that adding a single dovetail on each joint could be elegant and effective:

Properly done, this would be a great way to brag.

Another way to use a mechanical joint is to key the joint: I didn't have time to draw this one, but I hope to add it in the next few days...