Mortises by Router

The traditional methods of cutting mortises require fancy tools, or a lot of hand work with chisels and mallets.   Routers will cut nearly anything, but they are grabby.  Freehand router work is beyond my skills. Freehand, in my hands, the router wavers back and forth, cutting wavy lines.  I need  a guide for the router to cut straight lines.  To guide the router I fit a "template guide" aka schnozzle.   The schzozzle is big enough to pass the router bit clean thru itself, should the router bit contact the schozzle, bad things happen.  The outside of the schozzle  follows a wooden template.

This is a brass Porter Cable style template guide bushing (schozzle) mounted on my elderly Craftsman 1/4" router.  This clear acrylic base plate holding the guide bushing is shop made.  A 1/2" straight cutter pokes thru the schnozzle.   Here is the shop made template to guide the router in making a nice square mortise.

This is my shop made template.   The rectangular guide guide hole must be the size of the mortise, plus an allowance for the size of the schnozzle.  In this case the schnozzle is 0.75: in diameter covering a 0.50 inch cutter, so the template needs be 0.25 inches larger than the desired mortise size in both directions.  And, the template need be as thick as, or thicker than the schozzle is deep.  In this case I had to shim up my template to 5/8" to prevent the 5/8" schnozzle from getting stuck on the surface of the workpiece.  Rule: your template HAS to be thicker than the schnozzle is deep.  The bits of wood nailed to the template made a 1/2 plywood template thicker than the 5/8" schnozzle. 

And here is the final routed mortise.  Nice straight sidewalls, flat bottom.  I wanted a 0.50 inch deep mortise but settled for 0.47 inch, mostly because I didn't dare pull the cutter any further out of the chuck, lest it fly out and do evil things.