Larger drawing: http://www.gunlaug.no/att/div-2011/psg-var-5.png
I will use an iron "T" bar - shown as green on left part of the sketch above - as backbone for the aluminum neck. This "T" bar will go around a third the length of the neck, and have the vertical leg cut out so what is left can be "threaded" down between bellcrank axles and support profiles.
- 2 screws up through the neck at around 1st fret and 2 screws around 8th fret.
- Vibration dampening couplings - the type used for very small el-motors - will then hold the "T" bar onto 2 of the cross-profiles holding the frame for the bellcrank axles together.
When neck is mounted on top of frame, a vertical profile - which I imagine is easiest made out of iron plate - will be screwed onto the remaining lengths of vertical leg of the "T" bar and go full length of the neck below the bellcrank axles. The "T" bar and this vertical profile will form the around 5 inch high backbone for the neck together, thus make the relative thin and stepped neck pretty rigid and able to take up string tension without bending.
- To avoid bending caused by different thermal properties of aluminum and iron, only the 2 screws around 8th fret will be tightened hard and form a "zero" point. The screws at 1st fret will be just loose enough to allow for a tiny amount of horizontal slip but next to zero vertical movement.
- Under the bridge I will use "spring washers" to hold the aluminum neck down so I can tune the tiny amount of "metal-against-metal" vibration I want between the free-floating end of the neck and the backbone. This springy coupling will allow for horizontal slip, but not give much vertically under varying string tension.
To make sure the backbone put the right tension on the aluminum neck, a threaded rod will run along the entire length of the vertical profile attached to the "T" bar. By cutting into the vertical profile from below and in fact weakening it, nuts on the threaded rod can be used to trim the backbone's curve ever so slightly while giving it increased strength and rigidity.
Since I don't have a top-plate to mount keyhead with changer on, I will extend the backbone profile past the zero-fret all the way to the end. The threaded rod will then be used to tune and secure position and angle of keyhead, in effect pre-tension the entire string-mount.
Hope the above makes sense.