After reading a thread about box joints last week I was inspired to make a jig for my router table. It is just a sled that runs in the miter slots (I have one on both sides of the table). I ran the sled through the router with a 1/2" bit in place, and mounted a 1/2" piece of wood 1/2" from the slot. One piece of wood is held against the wood and run through the bit; then the cut out part is put on the wood, and so on. The mate is first run through at the edge of the slot, and then continued like the first.
The pieces dry-fit beautifully, no slop anywhere. I am using almost no glue because the parts fit together so tightly that most of it is coming out. After the glue dries some of the places actually have spaces in them. It is almost like the wood has shrunk a bit. The joint is plenty strong, but it isn't right; but I can't figure out what is going on. If anything the wood should be expanding, not shrinking. Maybe my joint is too tight, and not leaving any room for glue? I dunno.
Any insight would be much appreciated; I can't make any sense out of it.