I am starting a set of 10 dining chairs and have a few questions/problems
regarding complex angles on the tenons.

First a little background: A couple years ago I did a test chair which had
a curved back leg which was then rotated outward by about 15 degrees to
allow the legs to curve outward when viewed from the front and the side. To
get around complex angles on the joinery, I re-cut each face of the leg
such that it was at right angles to the cross rails attached to it. For
example, the inner face of the leg was cut to be at right angles to the back
seat rail and headrail. The back of the leg was square to the inner face.
The front face of the leg was angled out by about 6 degrees to be at right
angles to the side seat rail. The outer face of the leg was square to the
leg front face. This made the mortises and tenons very simple, all square
or only simple angles, but as you might guess, shaping the legs was quite
difficult and would be a problem in making 10 chairs.

For my 10 chairs I wanted to simplify the legs somewhat by not cutting each
face to be perpendicular to the rails. This now makes the mortices and
tenons more difficult. My plan was to still make the mortises perpendicular
to the face of the legs. However the tenons are then more difficult because
the shoulders are not perpendicular to any of the sides of the rails and the
cheeks are not in line with the rails in either plane. For example, on the
headrail, the tenons should be angled forward by about 15% to account for
the rotation of the leg, and downward by a few degrees to account for the
outward curve of the upper part of the leg.

Looking at the standard tenon jigs (Delta, etc), there appear to be some
limitations. If I tilt the blade by about 15 degrees to account for the
rotation of the inner leg face, and lean the rail forward on the face of the
fence by a few degrees to account for the outward angle of the leg, it looks
like I have to change the height of the blade between the two cheek cuts.
In addition, since the jig only allows the work piece to lean away from the
blade, I would need to figure out another way to lean it toward the blade
for the mirror image cut on the other end of the rail.


To do the tenon I am picturing it seems it would be better if the blade were
at 90 degrees and the fence that the rail is clamped to could be tilted away
from the blade at the top by the 15 degrees. I would also need to lean the
rail both toward and away from the blade to account for the mirror image cut
on the opposite end of the headrail. Perhaps wooden wedges at the
appropriate angles would help here? Does anyone have any ideas as to how to
handle this? How do other people handle this problem? Any suggestions will
be appreciated.

I know the above joints are difficult to explain in words. Let me know if i
can explain anything more thoroughly. Thanks in advance for your help.

Thanks,
Bob Abbott

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