As usual, click any photo to bring up a larger version.
This all started when I saw a post by Glenn Bradley over on the Familywoodworking.org forum about using his iBox boxjoint jig to make long pieces of fingerjointed wood and then interlocking them to make trivets.
But then my jig let me down.
Box joint jigs are designed cut finger joints in the ENDS of boards, not the FACE of boards. It was designed to clamp the board standing vertically on end.
See the gap there between the base and the sliding part? What I wanted to do, was to lay a board down flat on it's face, and then make a series of box joints in the face of it. But with that gap, there is no way to clamp it.
I later found out that Glenn had also run into a somewhat similar design limitation on his jig, and had to jury-rig up a method to hold his strips.
First, I went to my pile of short boards and found some likely pieces, resawed them down and planed them to a half-inch in thickness. I ended up with a some cherry and ash boards, like this.
Note that you don't want big boards here. My jig can really only handle boards that are up to around 12" long by about 7-8" wide. Other jigs will have other size limitations. It also depends on what size of trivet you are trying to make.
I could now clamp these properly in my jig. The vertical part of the L-shaped assembly could be clamped to the back of my jig. The horizontal part lay flat on the bottom, for cutting. I also took care to hold it flat at all times, as extra insurance.
I then proceeded to cut a whole series of 1/2" wide box joints in the face of the board.
Don't lose count! On my jig you move the jig by turning the crank. However since the board is face down you really can't see the cuts. So it is important to count carefully when advancing the jig. I was using a 1/4" blade, so it required making a cut, advancing 1/4" and making another cut, and then advancing 3/4" before starting over. Those alternating sizes of moves can throw you off.
Here is what I think is the clever part -- once done, I could then flip the board around so that the vertical part was now laying flat, and the face was now standing vertical, and then cut box joints on the other face as well!
Check out the results...
Take care when setting up the table saw. The width of the strips that you cut must exactly match the size of the box joints that you cut.
Full disclosure: I had trouble with not putting enough glue on several joints, and had to deal with some joint separation later, and the resulting mess of trying to pry things open and slip in more glue. THAT is why it is a good idea to practise with making a few before you start setting up a whole production line!
This was in a sense just a test, so I did not worry a whole lot about board sizes. The round one was just a fun experiment with some leftover scrap pieces. The rectangular one was a result of running out of strips.
I think the ideal size for a trivet is probably around 6"x6". So you should start out with boards that are either 7" long or 13" (to cut in half).