Hi, All -- I'm currently restoring a Bosendorfer 170 from 1912, that has been in my wife's family since about 1915 or so (story for another time). Instrument is beginning to have difficulty holding tune in some registers. Consensus is that re-pinning is appropriate, and my questions relate to that. Some background:
> I measured pin torque under string load and confirmed marginal (< 80 in/lbs) in many pins. Appears to have original 00 pins, so hardly a surprising result. In the overstrung basses pins are 000 and appear to be 90% original; the 10% that are a slightly different color mic out to be dimensionally identical to others. Pin torque in the overstrung register was consistently more robust as well.
> Pinblock: I have the frame out to assess the Pinblock and to facilitate some minor soundboard repairs. Pinblock appears to be sufficiently sound to not mandate replacement (I'm up to the task, but heck of a project on this instrument)
> After the pins were out and pinblock inspected, I saturated the sidewalls of all of the holes with thin cyanoacrylate. (It's an open hole pinblock, and in my experience in other situations, this helps seal end-grain and reduce moisture exchange during changing humidity, and hence improve dimensional stability.)
> Plan is to replace original 00 pins with 000 pins (setting aside the overstrung region for a moment). Will use Diamond pins.
> Preliminary results from test pins: To test where things are now at and to get a sense of where and how from here, I installed both a new 00 pin (as a control to see how holes may have changed after CA saturation) and a new 000 pin. Torque to get 00 loose as if tuning is 80 in/lbs (better, but still marginal). 000 pin measured 183 in/lbs - high! Granted, this is only 2 data points, and not under string tension.
> My question is this: is a reading of 180 in/lbs typical for going up a pin size? If that's too high, would anyone recommend marginally boring out the holes with a drill / reamer sized for 000 pins? If so, I would use a portable drill-press indexed to the angle of the holes. I'm going to install a few more 000 test pins to generate additional data points, but I really wanted to tap the collective wisdom here.
BTW, as you might have gathered, this is the first time doing a full restoration on a piano for me, and although I have repaired pianos from time to time, I would not presume to call myself a piano tech. I am however from a parallel universe, with a professional background in string instrument restoration, construction, research and instruction (violins, guitars, etc..) Pianos are fascinating! This instrument will remain in our family, and we look forward to reproducing some of the house concerts the instrument was used for in Vienna prior to 1938 (story for another time).
Thank you in advance (and more questions to come :-)
JF
-- John Fabel MS, IDSAInnovation, Entrepreneurship and Education
for Equity & Sustainability
> Physics & Engineering Faculty, Amherst Regional High School
> Generalist Entrepreneurial Mentor, Greentown Labs
> Adjunct Professor, Dept of Environmental Conservation / BCT
University of Massachusetts/Amherst