Fred, I wonder if bolstering the knuckles might take up that slop and give you a rounder knuckle? David I. ----- Original message ----------------------------------------> From: <fssturm@unm.edu> To: College and University Technicians <caut@ptg.org> Received: Mon, 22 Mar 2004 19:21:35 -0700 Subject: Re: Kawai heavy action > Today I visited the piano in question. Thought I'd report briefly on what I found. >Jim Harvey and Vince Mrkalo get the prize for best diagnosis at a cyber- >distance. > The piano is a KG-2, 1984, with wooden, Schwander style wipps, with carbon >jacks (no assist springs). My first diagnostic step was to measure DW and UW, >which were pretty consistent at 70 and 20 (+ or - 2 or so). Obviously friction >problems. Initial thoughts of weight problems as well, as BW calculates at 45. > I pulled the action, and checked for key friction. Nothing significant. Bushings >had more play than I like, so were plenty free. Applying side pressure, there was >no noticeable friction against key pins. Balance holes were pretty good (maybe >1/3 needed easing). > I pulled up on some hammers. A little working of those flanges revealed a >relatively mild case of the Asian Flange Flu (milder Japanese variety, not the >truly virulent Korean strain). I examined the knuckles. More slop between >leather and core than almost any I'd ever seen. > I figured I'd found my main culprits, so I did a little experimentation. I took three >adjacent keys, and >1) Proteked the hammer and wipp flanges, working them side to side (along the >length of the centerpins, not working them as a hinge. This is far more efficent >for getting Protek to do its best). >2) Brushed knuckles and applied powdered teflon. >3) Applied powdered teflon to the wipp cushions for good measure. > Now I re-measured DW and UW and found 48 (!?!) and 30. IOW, weight and >geometry are just fine, thank you. BW is actually a very workable 39. (If I should >want to reduce it, the hammers are nicely un-tapered, and a gram can easily be >removed by tapering, reducing everything at the front of the key by 5 gm). >Interesting how friction can work this way. It's not the first time I've measured >high DW and low UW and predicted not only a friction problem, but a weight >problem as well, only to find that when friction was removed the weight problem >was reduced. Goes to show you shouldn't place too much credence in formulas. >Sometimes down friction and up friction are not equal. I think this is also true >often with rubbing parts, but in the opposite direction. > I then tuned the piano, thinking over what I would propose to do. I ended up >bidding a one to 1 1/2 day job, intending to ream and repin all hammerflanges >(a hammer filing has to go along with this; fortunately the hammers aren't >grooved very deeply); detach one end of each knuckle leather, stretch and re- >glue, apply powdered teflon; do some other incidental friction removal, like >brushing, ironing, applying powdered teflon to wipp cushions; polish and >Mclube capstans; polish and mclube keypins; ease balance holes as needed. >And then a fairly rapid regulation, including making damper lift a bit later. Slam >dunk, I think. We'll see if they go for it. >Regards, >Fred Sturm >University of New Mexico >_______________________________________________ >caut list info: https://www.moypiano.com/resources/#archives
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