I was using plywood for practice, but decided to switch to solid wood, because in actual use, I will only be dovetailing solid wood. I planed a board down to 5/8 (at least I thought I did. More on that below) and cut some lengths to practice (and practice and practice.......) on.
I tried adjusting up and down, in and out, and it still wouldn't work right, so I decided to back up and look at EVERYTHING that went into making a drawer joint.
I first checked my chop saw. It was very slightly out of square, but I'm pretty sure that wasn't causing a joint problem. It would have just made a very slightly out of square drawer. Chop saw is sqare now.
I had bought a Milescraft Base Plate/Bushing Set
for my router. Every time I cut a joint, I noticed the router would move very slightly from one side to the other when I would go in and come back out. I just assumed the router bushing was slightly smaller than the jig notch. Then I happened to notice the insert was moving in the base.
Using my redneck engineering degree, I took some 1/32 thick black tape I have and cut 1/8 x 1 strips and stuck them on the outside edge of the insert as shims and got it tight. That made a world of difference. Now the joints were coming out almost right.
On some cuts, the guide would have a hairline gap between it and the right side of the board, and almost every test joint was off on one side and not the other. That's when I checked my board thickness and found on a 4 1/4board it was 1/32 thicker on one side. That was enough to throw the jig very slightly out of line and make one side of the joint wrong.
By then I had to go on a run. I got some 5/8 drawer stock from the shop I was working for this afternoon and expect the joints should work tomorrow. If everything besides the jig had been right, I probably would have had it set up fairly quickly.