Originally Posted by
J.R. Rutter
Not to muddy the waters, but here's what I do. I think that the lap joint that Peter described is best quality, but I personally would rather not have to do any more measuring and precision cutting than absolutely necessary. The method below only requires a grid to fit the door opening, then put away the measuring tools.
Glue up door without a panel so that you have a cope/stick corner joint.
Rabbet out the back side of the door with a router.
Make the grid with dadoed lap joints to fit the opening in the face of the door exactly.
Glue it in with typical end grain treatment (two glue applications a minute or so apart).
Set up the drill press with a 3/8" forstner bit set for about 1/8 - 3/16" depth with a fence that positions the bit right over the intersection of the muntin/mullion and the door frame.
Bore shallow hole at each intersection.
Use thick super glue, accelerator, 3/8 dowels, and a flush cut saw to create inset disks that span the joint and reinforce it.