Bruce, That thought about wood flanges and felt bushings working together crossed my mind when I was actively rebuilding pianos many years ago. So I did a test, and the results did not show any measureable difference between the flange materials. I bought a dozen new plastic flanges and a dozen new wood flanges, removed the original bushings and installed new ones so that they would all be the same. I sized them and fitted them with even and correct friction, and noted the humidity in the shop and put them in a box on the shelf. Every now and then I pulled them down and took new friction measurements, and made note of the friction on each flange and the humidity. After about a year I looked over the figures, and there was no significant difference between the wood and plastic flanges in how the friction changed. I had a range of 20% to 85% humidity, and while the friction changed a lot, both types changed the same. Unfortunately I did not save my notes, so I don't know the exact numbers. As I recall there were friction changes of about 3 grams from dry to wet, and they were quite consistent between all flanges. The reason for this, I think, is two fold: 1. the size of the hole in the wood flanges changed so little that it is difficult to measure. It is very small, and does not move enough to make an appreciable difference in pressure on the bushing. 2. The wood hole does not change evenly, but becomes slightly oval when enlarged. As a result, the hole size in one dimension hardly changes, keeping the pressure on the bushing / pin pretty much the same. If a more thorough or careful test were done with a larger sample and very carefully controlled humidity changes, it might be possible to find a slight difference between the wood and plastic flanges, but the difference would be miniscule - maybe 1/4 gram difference, which is below the threshold of reliable measurement with a manual spring gauge measurement. And also below the threshold of being important, in my opinion. Bruce, I would encourage you to do this test as a follow-up to your article. Bill Spurlock told me he did a similar test many years ago with the same results as mine, but I don't know if others have tried it. The problem Dave reported certainly is not a common thing. I have seen heavily used school pianos get loose jack bushings after being pounded hard for a few years, and a few tight bushings from time to time is not uncommon with any piano manufacturer. But loose pins in the birds-eye combined with tight bushings is really very strange, especially if it occurred in more than one note. As Mark Wisner mentioned, this kind of thing should get reported to us right away - no one should hesitate to contact Kawai about something like this. As Kawai has been using these materials for almost 40 years now, I think it is pretty safe to say we would be out of business if there were any consistent problems with the parts. :-) Don Mannino ----- Original Message ----- From: Bruce Dornfeld To: pianotech Sent: Saturday, January 03, 2009 7:24 PM Subject: Re: [pianotech] Kawai parts problem I have not seen these kinds of problems with Kawai actions here in the Chicago area. I agree with some of the observations that Dave Renaud has made. A couple of years ago, I wrote an article for the Partial Post, the newsletter of the North Shore Chapter. This is more controversial a thing than I would normally like to post, but here it is: The Weird Stuff: The Hole Truth By Bruce Dornfeld, RPT -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/pianotech_ptg.org/attachments/20090103/7293fd07/attachment.html>
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