While waiting for some finish to dry today, I decided to upgrade my 30 year old miter key jig that's starting to get worn.   In addition, I read an article recently about making a jig to cut spline mortises in box corners.   And I've admired using dovetail keys on corners.   So off we go.  Raided the pile of plywood cutoffs.  Glue is still drying so the thru cuts will be done when I need to use them for the first time.  (in my terminology, a key is across the joint line and is visible, so I use contrasting wood.  A spline is inside the glue line and is not usually visible from the outside)

 

One for keys that are straight.  I can use a rip blade for 1/8" keys, or a dado set for something larger.

 

One for the router table for straight or dovetail keys.  I will remove the fence and the guides will slide in the miter gauge slot

 

 

And one for stopped splines.  Put down stops and drop the piece into the bit and side to the other stop.

 

Cool idea!

Looks like I'm not done -- reading an old FWW today and there's a nice box joint jig for the table saw.   I have used IncraJig on router table, modified a miter gauge add on fence, made some for routers and flush cut bearing bits.  Might have to try one of these.