I would like to balance aesthetics and strength for a craftsman-style tusked tenon table frame. Are there rules of thumb to determine how close to the leg corner an apron should be?
(as a preamble, I should mention I'm working with construction grade lumber)
A tenon within a tenon
The particular construction I'm shooting for has one tenon passing through another tenon. And I feel this might require larger margins around mortises to prevent splitting failures in the leg's pommel (i.e. the upper part).
For a visual reference, I am trying to lay out the mortises in the piece (D) from the following picture, and I would like to know how to pick safe lengths for X, Y, Z (in green):
For assembling, piece (C) goes through the leg first, intersected by the other tenon piece (B), and finally locked in with one tusk on each leg. I am planning on chamfering the part of (C) which protrudes on the outer side of the leg.
My personal opinion is that it looks best if the mortises are off-center relative to the leg, closest to the outermost corner of the leg.
Additional details on the objective
The assembly plan above is accompanied with a FRONT+SIDE view diagram where all mortises appear to go through the center (i.e. not offset), as well as a picture where they clearly are offset. Those discrepancies and oversights seem to be par for the course in most of the project-books I've looked at this far. Is this only a matter of personal taste?
I'm trying to to something like the plan, without the lower shelf. In the absence of the shelf and lower rail, the "meat" (Z) between the top of the leg and the top of the mortises becomes more important. I'm doing this in thick pine stock (aprons are long 1.5"x3.5", and legs are roughly 3"x3").
Most other table plans I've seen place the outside face of the aprons very close, maybe 1/8", from the leg's corner (which places the mortises a third of the stock further inwards). But that might be a safe layout only for a hardwood leg. I can't assess from my limited experience.
Got the project description from this book: "Tables you can customize. Ernie Conover. published by Popular Woodworking Books. October 1995. ISBN: 1-55870-397-7."