Spline jig strengthens miter joints
Build the jig from 3⁄4 " MDF. Bevel one end of the rear cradle at 45-degrees, then glue it to the upright at a 45-degrees angle to the bottom edge of the upright. As you glue the front cradle in place, check that the two cradle pieces are 90-degrees to each other.
Next, cut the pieces for the saddle. The saddle fits over the tablesaw rip fence without any play, but still allows the jig to slide smoothly. When attaching the saddle, the upright/cradle assembly should rest on the table of the tablesaw.
To use the jig, make a mark on the bottom of the corner receiving the spline to indicate the depth of the kerf. Place the project in the cradle, and raise the blade so its highest tooth just touches that mark, as shown in the photo. Slide the jig back from the blade and reposition the rip fence to cut the kerf for the spline.