This will become the key levers.
Keyboard
This is barely started. All I've done so far is glue up a panel of 1/2" basswood, which the key levers will be cut out of once I finish doing all the gnarly math to decide where the jacks will be. This time I didn't try any funny stuff, it's just edge-glued and that worked well.
This will become the key levers.
I took a little poll of harpsichords to try to get an idea what the typical movement is in both key ends and jacks, so that I could figure out where the balance point should be for each key lever:
| Instrument | Keydip | Jack travel |
|
|---|---|---|---|
| naturals | sharps | ||
| 1979 Dowd franco-flemish (lower KB) | .25" | .30" | .3" |
| " " " (upper KB) | .25" | .30" | .5" |
| 1968 Dowd Italian | .30" | .30" | .4" |
| Lynette Tsiang double virginal | .35" | .25" | .4" |
| Zuckermann 5-octave concert | .35" | .35" | .4" |
I also measured the string spacing on my own harpsichords, and on the full-size drawing (which I hope is to scale) of the Zuckermann Italian Virginal kit. The wide spacing is the on-center spacing between narrow pairs of strings. On the regular harpsichords, the string spacing is dictated by the keyboard spacing (6 1/4" octave for Dowd, 6 7/16" for Zuckermann 5-octave concert harpsichord, 6 15/32" for Zuckermann virginal):
| Instrument | Narrow pair | Wide pair |
|---|---|---|
| 1979 Dowd franco-flemish | .10" | .524" |
| Zuckermann 5-octave concert | .10"-.125" | .539" |
| Zuckermann virginal | .11"-.12" | .46" |
Something that's very very obvious but I still managed to confuse myself over it anyway, is the fact that the balance points are chosen to get the desired ratio between keydip and jack travel. They have nothing to do with the actual center of gravity of the key lever. You decide the balance point to get the jack travel you want from the keydip you've chosen, and if the keys won't balance then you worry about clearancing/weighting them later.
Also, since in a virginal the jackrail is at an angle and the key levers vary in length (short in the bass, long in the treble), it makes sense to lighten the keys more and more as you go up, to try to get the moment of inertia to be equal (or as close as possible) for each key lever. Otherwise the treble will feel more sluggish than the bass, due to the higher mass of the longer key levers.
Another thing that's obvious but took me a minute, is choosing how the strings are paired. The strings are organized into pairs, which are closely spaced, but then in the wide gap between pairs you have space for two jacks, pointing in opposite directions. But should you start with one lone string in the bass (i.e. the upper string of a pair where the other is missing), or should you start with a pair of strings? My answer is that you should start with one lone string, because that means that the lowest jack will be in the between-pairs gap, i.e. on the far side of that lowest string (with its plectrum facing towards the front of the instrument) rather than the near side. This means that the lowest key lever is slightly longer than it would be if the lowest jack were on the near side of the lowest pair of strings. The key levers in the bass are not even long enough to get the balance point behind the name board, so you need every fraction of an inch of length that you can get.