Perfect Box Joints - on a Small CNC




This is a project I've been thinking about for a while. I love the look of crisp box joints but have never been pleased with cutting them out by hand. I have a small CNC, however, making crisp corner joints with a CNC requires a jig of some kind. Simply cutting out pins and tails on a flat board will cause the inside corners to be rounded.

After a good amount of testing, I made a little jig that mounts on the end of my small 3040 CNC. The jig holds the wood vertical so the joint can be cut cleanly. The jig is explained in the video, but is simply a piece of square stock bolted to the end of the spoil board.

The other "trick" to making the cuts crisp is to make a pocket cut that is larger than the wood your're using. I used Inkscape to design the joint and then ran the tool paths through Jscut (; both free programs.

The box joint came out very tight and clean. This opens up all kinds of possibilities for other projects too!

Video Link:

Thanks for taking a look!

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    3 Discussions


    3 years ago

    Nice thinking. Have you seen the hybrid pantorouter? I've been using it for box joints and dovetails, and have gotten some great results.


    3 years ago

    Interesting idea. Some people used similar procces to make curved dovetail-like joints by clamping one board parallel to the the bed, and the other perpendicular as in your jig. I just missed the engineering porn... You should have taped the cutting process.

    1 reply

    Reply 3 years ago

    Thanks for your comments. And, yes, there are other kinds of interesting joints that could be designed - I have a few in mind. Probably should have included some clips of the CNC zooming around. Watching this little 3040 CNC at 125 inches per minute is kinda cool. The thing that makes it possible to go fast is the router mod for the Dewalt - the stock 200 watt spindle could hardly do 60 ipm.