Here's the wood I've purchased for the keyboard and action parts. All bound up in a bundle, to try to keep stuff from warping too much. Basswood: pretty light wood, easy to machine, similar to balsa but in fact much denser than that. Several different dimensions (all 24" long), for the strikers and such; the keylevers themselves will be 3/8" x 3/16", and 12" long. Which is quite thin, I hope they are strong enough, especially after the several necessary holes are drilled through or into various places on these thin strips of wood. The intent is severalfold. For one, I hope that the thin and light levers will have low mass and low inertia, so that as much as possible of the acceleration work done to the key by the finger, is transferred to the strikers, which the keylevers fling (*) into collision with the strings. The strikers are basswood too, but they are of thicker dimensions, and they are necessarily pretty long to clear the wrestplank (about 3" long), so they've got some mass. I think I will probably "size" the strikers with Titebond glue, to try to prevent splitting; if they split anyway, or wear down quickly, or otherwise fail to cut it, I may have to try other, harder, woods for this.
Here I've started laying out the hole-markings for a set of four prototype keylevers, which I will construct to test out my ideas before committing to the full 49-key keyboard. Among many important parameters to verify, the most important is the "fulcrum point", i.e., where to drill the hole that a thick steel wire will pass through, forming the pivot point of the key-lever. If it were right in the middle, the key would be approximately balanced, and the motion ratio of striker to key would be about 1:1. However, I want a higher motion ratio, and I want the keys to have a positive gravity return, so the fulcrum will be located closer to the keys (i.e., the front end).
After all the complicated motions in the action of a modern piano, the effective motion ratio (as near as I can tell in my readings) usually works out to be around 5:1. So I take this as my upper practical limit, and I figure that I'll probably get some kind of satisfactory operation at lower ratios, too. Initially, I was planning to try about a 3:1 ratio first. But when I started laying out the keys, having already started to develop some intuitive sense for how they might operate, I just said what the heck and went for a higher ratio: my fulcrum point is at the 2" position from the front end of the 12" keylever, which would indeed imply a 5:1 ratio. In actuality, the ratio will be lower because the key surfaces extend more than another inch beyond the end of the lever, and also the striker is located an inch away from the back end of the lever, i.e., at the 11" position. (I measure all the distances from the front ends, to nullify inaccuracies both in the original nominal 24" length, and in my cutting down to 12", which can be up to 1mm or so, it seems.)
...Meanwhile, I've continued experimenting with arcade-cutters. My first one was promising, but it cut a little bit rough and also I thought the profile of the arcades produced was too deep. So I made a second one, with a shallower cutting slope. I had figured to file the cut edge to make it sharper, but actually the way I happened to position it when initially clipping the "ears" off with my mega-bolt-cutters, left a nice sawtooth bevel to the edge, facing the right way to cut in the direction of rotation. I guess the first time, this bevel ended up facing the opposite way. So, I just used my smaller tinsnips to put a few nicks of different depths into the sloped cutting edge, to produce the curved arcades.
Here I go, cutting this new arcade pattern into a poplar 1x2. I'll dice them up later: a little rectangle of wood containing only the top half of the circular pattern, will go on the front of each natural key.
Here, you can see the trapezoidal profile of my cutter, in the drill chuck. The almost-horizontal sloped edge is the cutting edge.
...And here are my four prototype keylevers, taking shape. Now I have drilled the 1/16" holes and threaded them onto #16 steel wire, which through no coincidence happens to be a nice tight fit. I "ease" the fit by bending the keylevers back and forth, but *not* up and down, thus giving enough looseness to pivot freely on the wire, without sacrificing the wire's ability to prevent the keylever from rocking back and forth on its long axis: which would cause the top ends of the strikers to move back and forth and interfere with each other. If the strikers still have too much side-to-side motion, I'll have to run them through a guide, but I'd like to minimize such sources of friction, especially in the region where motion will be 5x accelerated. (Side-to-side angling of the keylevers is not a problem, because they will be passing through guides, consisting of vertical "combs" of shiny nails, which constrain this motion.)
The brass eyehook thingies on the tops of the levers are for adjusting the damper heights. The dampers will come from underneath, just like the strikers, and they will be held in position by (globally adjustable) spring force. When a key is pressed down, it pulls upward on a pair of nylon monofilament ("fishing line") cords, which pass across two "pulleys" (possibly not moving parts, just smooth metal wire for low friction) and then pull the damper downward, against spring force. The monofilament attaches to the keylever via another drilled hole, which is located close to the fulcrum (1" away in the present design). Thus, the motion of the damper is at a low motion ratio, not the 5x of the striker. This reduces the spring force felt at the key, relative to how much is needed to be effective at the damper location. And it prevents unnecessary acceleration and travel of the dampers, which only need to move a fraction of the distance covered by the striker. And finally, it allows the dampers to come-from-beneath, which enables the entire action unit to be removed easily for service and adjustment: especially important given that my keylevers and "jacks" (strikers) are not separately-removable "in vitro", as they would be in a conventional harpsichord.
...So anyway, the eyehooks enable the monofilament to be "reeled in", thus setting the height of the dampers (or more precisely, they set the point in keytravel at which the dampers start to move and un-damp the string, which will critically affect the nature and feel of the articulation).
Just playing upon the raw keylevers like this, with my fingers, I can tell that the high motion ratio is good, I like how fast it makes the striker ends move, yet the levers are light enough that it doesn't feel like a harsh task to set them in motion, despite the leverage. I can play trills and repeats without lags or stutters. These levers are, by design, much more similar to the long, thin hammers that would be used with a hammer-dulcimer, than to anything you'd find under the hood of a piano.
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