I made one box using simple miter joints wanted to try doing miter joints with splines. The idea is miter joints glue end grain to end grain, which is a relatively weak joint. The joint can be strengthened by cutting small cross-cuts through the joint and filling it in with a piece of wood. This introduces additional glue surface against long grain and edge grain. I also think it looks neat and decorative. You can mix in contrasting wood or simply the same wood. You can also make the different sizes and angles.
To do this, I made a jig to run a 90-degree joint across the table saw blade. You can use any size blade you wish, whether thin kerf or a dado stack. This will safely move a workpiece across the table saw and also allow for repeatable cuts. I found this design on Sketup 3D Warehouse. I liked it because it’s versatile and I’ve also been wanting to mess with t-track. Two holder pieces are secured via knobs dial and move the width of the jig. You can lock it down and keep the workpiece between the holders secure.
To cut the splines, I cut off a narrow 3/16 or so strip of wood, then cut into small pieces. For such a narrow piece, I cut off my piece on the left of the blade from a larger board rather than trying to run a such a narrow strip against the saw fence. Rockler makes a nifty jig for this task, although you could do it with a feather board.
I had assembled the box using tape and then pulled it tight with a strap clamp. After the glue dried, I kept the tape in place and that seems to help keep the spline glue off of the box surface. Then I use a flexible flush saw to trim flush with the box. Easiest next step for me seems to just sand it down flat, but I’m messed around with chisels and a block plane too.
The tricky part is getting the saw depth right. You want to go as deep as you can without cutting through into the inside of the box. The box in the picture below is only 1/4 inch thick. Seems a good idea to do 3/8 sides. You may also want to use a flat-top blade to make a flat cut, but I just used by ATB, which creates a little V. ATB seemed to work fine.
I have two example below, Both are using the standard kerf blade. One is a bigger box with 3/8-inch sides. The finished picture below is a 1/4-inch box that’s trimmed, sanded, and complete.