I thought about writing my response so as not to get that reply, but I was too
What's that rule? The walls of the mortise shouldn't be any thinner than the
thickness of the tenon? For example, a M&T joint in 3/4" stock shouldn't have
a tenon any thicker than 1/4"; Zat sound right?
See Nad. See Nad go. Go Nad!
To reply, eat the taco.
A guide from my days doing machine design.
Allow the tenon to be 50% of the stock thickness which means the
cheeks of the mortise will each be 25% of the stock thickness.
Based on the above, for a piece of 3/4" stock, the tenon would be 3/8"
thick and each cheek will be 3/16" thick.
The cheeks and the tenon equally share the load, thus have equal total
Works for me.
For machine cut mortises, the walls of the mortise combined shouldn't be
thinner than the thickness of the tenon. This equalizes the amount of
wood in each component. For 3/4" stock, the tenon should be 3/8".
For hand-cut mortises, you'll often see the 1/3" rule, which results in
1/4" tenons. There are two reasons given for this: 1) hand cutting is
harder on the piece being mortised, so this gives a bit more wall
strength, and 2) it's quicker to cut a 1/4" mortise since you're
removing only half the material.
And note that it's the thickness of the piece being mortised that is the
main criteria here...there's no real downside of having a fat tenon on
the piece being tenoned as long as there is still some shoulder left.
So if you have a table apron joining with a thicker leg, you can use a
tenon thicker than half the thickness of the apron.
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