About a year and a half ago, I did something similar to my B.? At rest the key fulcrum would be at the back of the felt.? Depressed it is at the front.? I cut my balance rail felts so only the back portion is there.? The cut line is on the back side of the pin, so not even one half the felt is there. I put just a small drop of glue on the bottom of the key.? (behind where the pin is).? Then set the key down on the key frame with the whole felt in place.? Let it dry, then when you take the key off the key frame it pulls the felt with it.? Then trimmed the felt with a razor blade. My B is a 1917 and has a balance rail that's ratio actually changes from bass to treble.? Key 1 had a ratio of about 5.2 as where key 88 was up around 6! This change gave me aprox. 6.5 grams reduction in touch and required adding fifteen thousandths of key dip do give the same hammer blow. Really helped! Denis Ikeler www.ikelerpiano.com -----Original Message----- From: Fred Sturm <fssturm at unm.edu> To: College & University Technicians <caut at ptg.org> Sent: Fri, Oct 2, 2009 3:31 pm Subject: [CAUT] fulcrum of a key I've been thinking quite a bit lately about just exactly where the fulcrum of a key is. One thing that got me thinking about the question was David Stanwood's adjustable ratio design. It uses a fairly sharp and precise fulcrum, that slides from behind the balance pin to in front of the pin, a total of 8 mm, and changes the action ratio in the range of from about 5:1 to 6:1. This is from about 2 mm behind the pin to 2 mm in front.? ? I have just been working on an action where I made use of sliced punchings: felt balance punchings trimmed a bit (I bought them from Pianoforte Supply, Crescendo punchings "accelerated"). They are sliced about 1.5 to 2 mm from one side, so that there is a straight line, which is put to the front of the key. That reduced touch weight a bit (by changing the ratio), but not nearly enough, so I added half card punchings glued to the bottom of the key (glued to the behind side of the balance hole). Those two things put together got me a reduction of about 10 grams. (It was an action that I would normally have switched from 15.5 knuckles to 17.5, but all the parts were near new, so I thought I'd try something else).? ? Now I figure that my half cardboard punchings are, actually, putting the fulcrum pretty darned near the center of the balance pin. So it gets me wondering where, exactly, the effective fulcrum of a standard set up is. Obviously it must be somewhere in front of the pin. Since using felt punchings with about 1.5 mm trimmed from the front changes the touchweight measurably, it seems like the effective point might actually be near the front of the felt punching.? ? As an aside, but somewhat relevant, the Steinway accelerated half dowel bearings actually have a moving fulcrum (as the key bottom rolls along the bearing), which "accelerates": it changes the ratio as you depress the key.? ? This question has some relevance to issues like what kind of material is used for the balance punching (relatively spongy felt versus crescendo, for instance), how high paper and cardboard punchings are stacked, and maybe some other things as well. It may explain why geometrical measurements of kay ratios and action parts don't predict the actual action ratio (since we typically use the center of the balance hole as the key fulcrum).? ? Has anyone out there given this much thought and come up with some conclusions?? Regards,? Fred Sturm? University of New Mexico? fssturm at unm.edu? ? ? ? -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/caut.php/attachments/20091002/e08a8871/attachment.htm>
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