I've been working on this one for a couple of weeks, off and on--a jig to cut box ends at a 45-degree angle. The basic jig wasn't all that hard to build--a base out of Baltic birch plywood, runners out of UHMW to fit in the miter track of my table saw, and front and rear fences out of soft maple. The real trick was to get the front fence squared up at exactly 90-degrees to the saw blade.
I tried several techniques before I got it right. First, I used my Wixey electronic digital protractor to try and measure to the angle to the blade. This proved to be highly inaccurate, given that the blade was leaning at the necessary 45-degree angle to the base. Then I tried cutting boards to measure the resulting angle by trial and error. At first I used a narrow board but found that too inaccurate also. Finally, I used a 5-inch wide board and after many tries was able to get the fence adjusted spot on to 90-degrees.
The plan now is to make tissue box covers using some highly figured quartersawn sycamore I was able to get hold of. That'll be the test of just how accurate the fence really is. The good news is that I can always make more adjustments if I need to.
Before I start on that, I want to hook up my dust collection system, now that my hoses and connectors have come in. But who knows, I may not be able to contain myself from building an actual project before I get that done!