First off, let me say that I’m no woodworking professional, and not even a good hobbyist. I love to experiment with stuff, and after I saw something on wooden box joints, I tried to make some of these on my manual mill. Eventually maybe I’ll try some on my CNC router, but this is my first try at it on my milling machine.
Box joints are a method of fastening two pieces of wood together by putting carefully spaced slots in the sides and gluing them together. These slots can form a male and female end so to make a four sided box 2 of each type are needed or 4 sides with one male and one female end.
These joints are generally made with a table saw or router, but what I had available was a milling machine meant for metal. The first variation I made with plywood using a 1/2 inch end mill. When set up, it’s 1 inch or 10 cranks of my X-axis handle before I would plunge into it. Unfortunately, the wood tended to split when the cutter exited from the other side. I think this was because the maximum RPM that I used with my mill was around 1200, this made the wood tend to splinter instead of cutting cleanly. Woodworking is generally done with a higher speed cutter.
The same thing happened with the 1/4 inch end mill that I used with the smaller joints. The quarter-inch, as with the half-inch mill worked out well because it was exactly 5 cranks between the joints. Other size end mills could have been used, but without a digital readout (DRO) it would have been hard to accurately keep track of everything.
With both these cuts, the depth needs to be the same as the width of your workpiece so that the joints seat securely without poking out. Put a little wood glue between the joints before pushing (or pounding) them together and use a square to assure everything is parallel. Let it dry and you’ll have a very strong bond between the pieces.
This was my first try at this, and as an experiment I’ll consider it successful. If you’d rather check out someone’s site who actually knows what he’s doing (who also made a cool gear template that I’ve used), check out woodgears.ca, or just watch his video below about a computer-controlled jig for making joints like this that he made: