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I'm designing a trestle table with tusk tenons on the stretchers and need help with proportions. The leg assemblies for the table will have two uprights, each 2 1/8 inch square. Stretchers 4 inches by 5/4 thick will run between the legs and will be about 13 inches off the floor. (there are another pair of stretchers at the top of the leg assembly, directly under the table top.) I've currently designed the tusk tenons on the stretchers to fit into a through mortise that will be 7/8 inch thick by about 3 1/2 inch high. I used 7/8 inch because its slightly more than 1/3 the total width of the leg and is thick enough to allow me to cut the mortise for the wedge. The mortise for the wedge will be 3/8 inch wide, leaving 1/4 inch of wood on each side of the mortise.
Questions: 1.) Is the mortise for the tusk so wide that it will structurally weaken the legs? If so, what would be the right width? 2.) Is 3/8 inches to wide for the mortise for the wedge? If so, what would be a good width. 3.) Authors seem to be all over the lot as to the right angle for the slope on the wedge. Ian Kirby says 5 degrees, others say 6 or 7 degrees, and at least 2 authors say 10 degrees. I'm inclined to go with the 5 degrees because Kirby has a lot of experience.
Note: The leg assemblies are already dimensioned and mortise and tenons cut to mount the legs into the top and bottom of the leg assemblies so I don't want to change the 2 1/8 inch square legs. Wider might have been better but this width looks good in the design.