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I haven't cut 'actual' mortise and tenons with a router yet, though I look forward to learning the ropes in that area.
I would most likely mount the router on ski's to cut the mortise. I equate cutting a mortise to cutting a 'slot that does not penetrate the workpiece entirely'. I have cut some slots on a router table, but have come to believe, skis are a much better way to do that.
The tenon portion is very similar to a lot of the rabbet cuts I have made, it's just four of them per tenon. To do those cuts, using a router, I would do it mounted in a table.
wbh1963 is flowing with the grain in Arlington, Washington, USA
A day without curls is like a day without sunshine!