Every now & then, a post comes up regarding box joint jigs. Everyone posts their regular old box joint jigs, not that there's anything wrong with them, of course.
But this one seems much more flexible to me. There's no cumulative error, and the spacing can change from one project to the next with no changes to the jig.
Plans & photos are hosted by the LeeWay Workshop the address below.
I recommend saving the photos, text and plan to your hard drive, as the site hosting this plan disappears from time to time. I couldn't find it for a year or so there...