Round Mortise with Square Tenon?

Bob Beasley

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I see folks cutting mortise holes with routers. This leaves a nice rectangle with round edges. Then they cut rectangular tenons with square shoulders to go in the mortise. I don't really understand this. Is this a strong join? Perhaps I just watch too many youtube videos?

Many Thanks!
 
Router mortises are unfailingly perfectly perpendicular and perfectly sized. Tenons with square corners are easier to mill. The conundrum is to square the corners of the mortise or round the corners of the tenon. For me, it is tons easier (and faster) to pare the square corners round than to mess up the geometry of the mortises. A sharp chisel and learning some simple body mechanics in using it and bob's yer uncle.
 
My choice has been to go the route of loose tenon joinery. There are several advantages to this process. Basically, you make the mortises with a router and get rounded ends. After making tenon stock to proper thickness, round over the edges to match the mortise.
 
Okay, I read up on loose tenon joinery and it seems like a good place for me to start. Got a couple of questions.

To "round over the tenon" am I passing the cut to size tenon stock over a round over bit on four sides?

Uh Oh math may be required here, If I have 1/2" thick tenon stock to go into a 1/2" mortise I would use a 1/4" radius round over bit?

Thank you all for your patience!
 
Is there a recommended ratio of thickness of wood to thickness of mortise? For example if I had a 1" thick piece of wood would I cut a 1/2" mortise, leaving 1/4" top and bottom of the mortise?

Same question for length of mortise relative to width of joining wood? Seems like this would be very important when doing loose Tenoning.
 
Is there a recommended ratio of thickness of wood to thickness of mortise? For example if I had a 1" thick piece of wood would I cut a 1/2" mortise, leaving 1/4" top and bottom of the mortise?

Same question for length of mortise relative to width of joining wood? Seems like this would be very important when doing loose Tenoning.

With regard to the thickness of the tendon, or width of mortise, this example is often used because 3/4" thick material is so very common; 1/2 the thickness, meaning a 3/8" thick tenon, leaving 2 equal shoulders (usually) of 3/16".

with regard to the length of the tenon, so many variables, but all things being equal, 5/8 to 3/4 times the width of the material of the mortise. Example, a 2 1/2" wide stile would safely receive a 1 1/2" to 1 7/8" long tenon. Be aware other joinery or hardware may require some adjustments.
 
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