I am restoring a 1950's Neupert harpsichord to make it playable. Three problems are immediately noticeable.
I do not regard this harpsichord as historic and my primary goal is to get it to be fully playable and to sound good. Trying to undo the cosmetic effects of the water damage is something I will leave for later, or never, or for someone else. So my first task is to properly requill all of the jacks in delrin. The jacks are metal and seem to work fine, but the plectrum mortise is much too big for a delrin plectrum. The two options I considered were replacing the tongues on all of the jacks with tongues with small mortises, or filling the space with something so that delrin plectra can fit tightly. The latter option was chosen because it seems less risky, more reversible, and less complicated.
The mortise dimensions are as follows:
My procedure for fitting delrin plectra to the big mortise is as follows. One foot of 1/8" x 1/8" brass I-beam stock was bought from Pearl Paint, and also some 0.025" brass sheet stock. The I-beam was ground down from 0.127" to 0.121" in both dimensions. A 0.120" length of the I-beam was cut off using a cutoff wheel in my Dremel at medium speed. This short piece of I-beam was inserted into the bottom of the plectrum mortise in the tongue so as to appear as an "H" when the jack is viewed in its normal vertical operating poition. It is a snug press fit. A 0.070" x 0.120" rectangle of 0.025" brass sheet was placed on top of the cross-member of the "H". The plectrum, when inserted between the top of the rectangular piece of sheet stock and the top of the mortise, is held very tightly. This can be seen in this picture of the back of the tongue, and this picture of the front of the tongue. The desired slight upward angle of the plectra can be set with the tongue stop adjustment screw on the jack. I have not tested this yet because the harpsichord is in DC and I am in NYC. I am working on how to get it up to NYC without spending a lot of money or subjecting the instrument to any sort of violence.
Update (May 2009): The method described above was too tedious. I found that it is possible to achieve the same result with a wooden spacer instead of brass. I did that for all of the plectra on the 4' rank. It is pretty good now. I'm waiting for the 0.020" plectra to come in the mail so I can do the 8' rank. It is very pleasing to hear the 4' working.