[The following is an article I wrote for a woodworking club’s newsletter. It’s about making the small box I have just listed in My Projects showing the compound miter joint. Click on the links as you read to see pictures.]
Sometimes the simpler they look, the more difficult they are to make. In the small box shown here, I was challenged with a joint that I had not preciously seen. I don’t know what it’s called, but I refer to it as an “interlocking miter joint”. It’s a combination of a simple lap joint and a meter joint. There are probably not too many applications where this would be used, but because it’s so unusual, and rather attractive, I thought that readers would like to see how it’s made.
I started with some old salvaged timber given to me by a friend. He didn’t know what it was, but assured me that an expert timber supplier had looked at it and determined that it was California Redwood. I was dubious at the time, but didn’t give it much more thought. I now believe it is Douglas Fir.
Originally from a grand old Victorian home that was demolished in Melbourne about fifteen years ago, the timber was used in an architectural feature in the house. It was coated with several layers of white enamel paint which hid the beauty of the timber below. After checking for nails and screws with my metal detector, I stripped the paint using some old blades in my planer.
The timber was milled to a thickness of about 12mm. As you would expect, the box has four sides, but I milled some additional pieces, because I knew I was about to embark on a trial-and error process. As I would shortly discover, this was a smart decision.
Like all joinery, it is essential that all of the pieces are square, and of uniform thickness and dimensions. You must sand the timber to finish smoothness at this stage. You cannot do so after milling the joints, because doing so will cause the fit of the joints to be sloppy. Once this was achieved, I started on the cuts for the joint. The first milling process is to cut a dado on the face of both ends.
This can be done on the router table, but in my case I used a dado blade on my table saw. The calculation for the location of the dado is simple. From the end of the piece, measure a distance equal to the thickness dimension of the timber being used. This marks the outside wall of the dado which is cut to half the thickness of the timber. The width of the dado is exactly half the width of the timber you are milling.
The next step is to cut the half-lap dado cut across the edges of these pieces in exactly the same location as the face dados. Adjust the dado blade for height, and use a backing board to prevent tear-out. Make sure that you cut these on the same surface at either end, as there is potential for a mistake when you flip the piece from one end to the other.
Now cut the outside shoulder to a 45 degree bevel. [See the yellow oval in picture.] I chose to cut the bevel with my table saw. It is this cut that is the most crucial in this joint. The apex of the angle must start exactly in the bottom corner of the dado where the dado wall meets the floor of the dado. Even a minor error here results in a joint that is too tight or too sloppy. It will be too tight if you have created a step at the bottom of the cut, or too wide if you have widened the width of the bottom of the dado.
Before cutting all of the pieces, test fit two sides. They should go together snugly, but without force. The pieces are rather fragile before gluing, so any force will likely result in one of the end pieces breaking off. When you are satisfied that the joint fits properly, cut the balance of the pieces.
Dry assemble the four sides of the box. If it is out of square in the slightest, it will not be possible to slide the lapping pieces together without undue force. When you have four sides that assemble easily with no slop, apply the glue to the joint surfaces. This joint will become very strong once glued together as there is a lot of glue surface to each joint.
When assembled, the box should look something like this.
-- CanuckDon "I just love small wooden boxes!" http://dpb-photography.me/