I set the blade -1/64 approx. less than the thickness of the sides, and cut all way around then use a utility knife to remove the top. I was taught this many moons ago, and it works good for me.the thin sliver can be removed easily with a sanding block.
Are you cutting with the top against the fence, or the bottom against the fence? I try to do the cutting with the bottom against the fence , unless the box is too large, it gives you more surface to square up the cut.
An other option is to cut the top off on the band saw, just one pass through will do the job, the only con about that is that cut will take a little more sanding to remove the kerf marks.
Last edited by Herb Stoops; 03-08-2019 at 12:49 PM.