Kawai heavy action

[David Ilvedson]

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
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