felt and striker springs

Some incremental progress since last time...  Here, inserting the guide-nails into the keylevers, which the strikers ride upon.

Same glue-nail-heads-into-place procedure as with the pedalboard, just at a smaller scale!

Making the felt for the lower keylever travel stop.  I ended up using two layers of my fairly-thin felt here.  This felt pad quiets the key on the return stroke; if the finger is snapped off the key rapidly enough, the key accelerates under gravity until hitting this felt, so there can be substantial noise; but still, the upper travel stop is more critical (or at least, it receives more force): the upper felt terminates the "power stroke" which actually launches the striker.  It "feels" like the abruptness of impact with the upper stop somehow plays a part in imparting speed to the striker; but according to my understanding of the laws of physics, the striker will move just as fast even if the keylever is brought to a stop slowly and smoothly (and quietly) by a thick layer of felt.  I will "intuitively" believe this only once I actually feel it under my fingers...

These little felt pads on the keylevers under each striker are a crucial element of my design idea.  This is what is supposed to damp out any tendency of the striker to bounce off of the keylever and return to hit the string more than once.  Piano and piano-forte actions use all kinds of complicated catch mechanisms to prevent a rebound of the hammer, while also keeping the hammer near the string, ready for a quick repetition.  If my trivially-simple felt-and-spring system can accomplish a similar task, I'll be thrilled!  Only by actually building this action, and playing it for a while, will I really be able to tell whether the complex interaction of striker mass, lever lengths, spring strength, key travel distance, striker flight distance ("regulation gap"), and felt absorptive and frictional properties, leads to success (which is defined as that highly-subjective, "I'll know it when I feel it" quality known as "playability").

I was planning to glue the springs into the keylevers, but they jam into the holes so nicely that I think no glue is needed; and I may decide to change to a different wire guage to change the spring strength, so I keep my options open.  Indeed, the best way to remove the strikers, perhaps to sand them more/differently or to add felt, might be to pull out the springs from the keylevers; otherwise, the springs would have to be bent beyond the linear domain to get the strikers off the long guide nails, necessitating a tedious re-bending of each spring to get back to a good action again once the strikers are replaced.  Phew, it's tedious even to write about!  Anyway, so I think removable striker springs is a necessary feature of this action design, which I'll carry over to the big instrument (next project).

The strip of wood in place at the top of the guide nails is not what will really go there; I'm just using the damper spring carriage, since it has the right-sized holes at the right spacing, to stand in for the upper travel stop.  This has allowed me to test the action, ever so crudely, by holding the zither upside down above the strikers.  (Eventually, the zither will rest in a cradle which holds it at exactly the right distance.)  Another test is to hold a finger just above the key-down rest position of one of the strikers, and then hit the associated key.  Although the striker moves so fast that it's hard to see it leave its felt pad, one can feel the momentary touch of the striker, even for very soft strokes on the key, when the fingertip is hovering 1/16" .. 1/8" above that rest position.  These are all good omens...