more carving, and issues with the frame design

Since last time, I've done a few additional bits of machining to the main timbers.
Also, however, just by laying out the frame pieces and thinking about the issues, I've realized that the frame as it stands will probably not work: at least one additional piece of lumber will be needed.

I used my "mitre cut guide" for the first time in earnest, and already, I'm not using it according to the "instructions".  It turns out to be my best-available way to make straight 90-degree cuts, too.  I clamped the timbers in question to the nice, flat, square faces of the prefinished 1x3 comprising the inner upright of the guide.  Thus, I obtained nice flat surfaces for the wrestplank to fit into, in the frame.
I wasn't planning to use the guide in this way (particularly the way I made the long cuts), but it worked adequately.  Glad I used the prefinished 1x3s and not regular 1x3s in those positions!

A carve-out is needed on the horizontal timber, timber 6, for the treble end of the soundboard. Like the other soundboard carve-out, this cut does not need to be precise; my little hand-saw with the "shark teeth" did the job.

Also, I drilled the four perimeter mounting holes for the wrestplank (but not, yet, all the inner holes for the tuners (98) and other items; I will lay these out after the frame is assembled and finished, so that the tuning pegs will contact bare unfinished wood).

I think I have a design problem with the frame, at the joint between the cheek and "bentside".  In my original design, the plywood bottom was to have extended under the keyboard as a single piece, and this is the impression conveyed when I lay out the frame timbers upon the sheets of plywood as above, because the plywood pieces are not trimmed to their to final shapes yet.  Actually, the bottom plywood will more or less mirror the soundboard in outline, extending only to the horizontal "belly rail".  The keyboard will be removable from the bottom, a necessity given the design of my dulce-melos action.  There will probably be a separate removable plywood floor to which the keyboard rails are attached; or there may be no floor at all, just an open frame primarily composed of the keyboard rails themselves.  Either way, no structural rigidity can be counted on from this area, the instrument must be fully stable under tension with or without the keyboard present (indeed, I don't plan to even start building the keyboard until after the frame is already built, finished, and under tension).  The end of the long spine timber on the left, and the parallel short cheek timber on the right, need to project like tines of a fork and support the wrestplank, with all its tension and twisting force.  The spine side has innate resistance to twisting by virtue of being one long piece of wood, but the short cheek piece is in a poor leverage situation.

Given the lack of "floor", the cheek frame piece appears to be insufficiently supported; the wrestplank will of course exert a large twisting force which the closely-spaced joints to the other timbers don't have much chance of opposing.  There will be additional strength contributed by the outer case, but that will mostly be effective for preventing flex in long members such as the spine piece; the case won't contribute the type of strength that is needed here.

I think I want some kind of diagonal brace underneath the level of the keyboard, and under the floor of the sound cavity.  I hope to still keep the height of the case sides the same, my relatively narrow 1x6 lumber (not 6 inches of course); but there is a progressive shift to lower sides, less on top.  Originally the sides would have been one plywood thickness lower than the bottom face of the frame 2x4s.

I suppose, in a larger-scale redesign, one might try to make the cheek piece longer, and make the joints to the other timbers more separated, so that more rigidity is imparted to the cheek.  Even a small amount might help the leverage.  However, I think the cheek still would need a brace to give it "box strength".  Frankly, the plywood floor, even reinforced by the keyboard rails, would not be enough to give the needed strength even if it were permanently attached.  Its removal in this design just helped alert me to the issue.

Just shows how much the entire design is in-flux.  I try to avoid starting again entirely from-scratch, but it can happen in projects like this.  All I know is the result that I need to see, and to hear; how to get there, I make up from moment to moment!