Each time I build a project that requires box (finger) joints I scab together a quick jig anf have at it.. I guess I have been lucky as it works most of the time. However I found out that you have to be more accurate especially on wide panels.
My last project required a box joint on 12 ¾ “sides. My test pieces worked out fine so I went ahead and cut the work-pieces. Unfortunately my test pieces were only about 3 ½ “wide. When I fit the 12” boards they started out great but by the end they were out and did not line up. The moral of this story is jig accuracy is vital over a long span.
So I designed this jig with micro adjust capabilities now I can dial in the exact width between the cut and the registration key, down to thousands of an inch.
The jig is fairly simple to build but will be an invaluable tool in the shop. The othr alternative is to purchase a commercially made jig for a couple of hundred dollars