![Image](http://www.gunlaug.no/att/div-2011/keyhead-changer-1.jpg)
Raise and lower made of steel plate, U-shaped, with raise inside lower. Knife-edges reinforced with shaped steel plates "welded" with heat-cured epoxy inside the U-shaped raise and lower parts.
Acts like a regular pair of scissors. For raise it is forcing the keyhead slide for each key away from the edge fixed to the neck-bearing, and for lower it lets the slide be pulled by string-tension.
Lower-return is (to be) achieved via a push-rod in the "lone" upper lower position, and I have several reasons for this solution.
1: no "reverse-effect" if/when lower-rod is pulled far.
2: I can use a long spring for constant return-force since the spring will be hooked up at the bottom of freewheeling bell-cranks 10-15 cm from the changer.
3: by pushing at the front-end of the changer-finger, instead of at the back-end, the changer-fingers will naturally line up straight and not tend to "wiggle". The fixed line-up of this push-rod between changer and bell-crank, will also will also steady the changer.
4: this arrangement gives me an extra lower since I can pull anywhere on the freewheeling bell-cranks. Much needed extra for my JI-tuned pedal combinations.
Only potential drawback for this lower-return variant is that knife-edge will lose contact if spring-push is adjusted too high.
Drawing does not show exact positions for knife edges and shapes of parts, as I have to test on a one-string prototype to get the +/- 4 millimeter slide I need before raise and lower lock into each other and neutralize further change - a design-feature.
Also have to make sure I can remove the raise from its place inside lower for maintenance, without risking "self-disassembly" while playing or replacing strings.
All knife edges will be made as sharp as a blunt knife, so I have to make sure I get the material and angles right for edges and seats.
That's all I have drawn so far ... the rest is in my head.