Keith, thank you for your thorough investigation of wool and center pinning and what spec should be.
I disagree with what you consider to be ideal lack of friction in a hammer center, which appears to be exactly what Steinway recommends: it can be as free as possible so long as there is no side play. While the source of this opinion of course makes disagreeing with it a daunting prospect, I cannot help but go along with my own observations instead of received wisdom.
Consider the uses of friction in an action, especially hammer friction. When the friction gets so low that a hammer has 10 swings or more, it kicks and FLUTTERS coming out of check. Worse, if the spring tension is high enough for firm and rapid resetting of the jack (fly) under the knuckle (roller), it sometimes won't even get firmly into check. It can toy with the backcheck, but then the spring tension is greater than its friction against the check leather, and it pops back out of check, especially on a light blow.
When the hammer gets out of check, if it is too free one can feel a real clunk in the key as the spring kicks in. Kicks.
Or, if someone decides to favor secure checking rather than speed and dependability of the note resetting, the springs are left too weak and repetition suffers. Without hammers being able to check high enough, fast loud repetition is impossible. I was very struck by a slow motion film which I saw at a convention (I believe it was done by Kawai.) A hapless pianist was assigned the task of repeating a note ten times a second (well, my memory may be faulty, but it was something like that), and photographs in extra slow motion were made. It was amazing to see the flexing and side play in the hammer shank, but what amazed me more was to see that even at that lightning speed, the hammer went into check after every single note. If a note doesn't check dependably, and check fairly high, it will not repeat properly.
And when there is not enough friction but the spring is strong enough for fast playing, hammers, especially in the tenor, won't go into check after a soft blow, but only when played more loudly. Instead, they flutter around. If the letoff and drop have been regulated really tightly, the hammer often will double strike when it is fluttering up and down like that. I HATE that, hearing a double strike when someone is attempting to play softly.
So, what is the ideal situation for soft playing in a concert? I would describe it as smooth as silk, with the notes totally dependable even at the lowest possible dynamic level. I know that when I repinned a D action to Horace's "spec", I ended up with dependable checking at mezzo piano right down through the tenor section, with no doublestriking and extremely good control, so that notes wouldn't refuse to speak. And the artists have used that control at every opportunity.
Build it, they will come. They never complained before, but after I did that repinning, they definitely used the extremely soft dynamic levels more often.
When there is enough friction in the hammer (assuming other centers are reasonably close to spec), it will resist the spring enough that it doesn't jolt upwards, but smoothly rises. It will go into check. It will not double strike even with tight letoff and drop.
Your mileage may vary. The West Coast climate is very forgiving, so if one puts a certain amount of friction into a center, it will not seize up in a damp time of year.
As for daring to disagree with Steinway's recommendation, I didn't. This hammer friction spec IS from Steinway. The actual one was "3 to 5 grams". It just was pre-Teflon I Steinway. I think that the "as free as possible but no sideplay" idea may have been attempting to make a virtue of necessity, since teflon bushings made it impossible to keep a dependable moderate friction in the center. But then, who am I to say so?
I can't help it. For me, direct observation will always carry more weight than pronouncements, whatever the source.
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Susan Kline
Philomath, Oregon
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Original Message:
Sent: 12-28-2017 02:05
From: Keith Akins
Subject: teflon impregnated action center bushing cloth
Well, there are multiple issues here to explore in depth...
1) I appreciate and use the 5-swing test for regular, non-teflon-bushed flanges. However, we need to reflect a moment on where that specification/rule-of-thumb came from. Or rather where it did not come from ... which is some ultimate specification handed down from on high that it correlates with what friction should be. Rather, as happens so often with pianos, it represents a "goldilocks zone" of where lateral joint rigidity and freedom of movement occur with the non-ideal materials of wool and wood fitted with a metal pin. IOW, friction ideal would be less but then the joint would be too wobbly resulting in poor tone and greater hammer wear while joint rigidity would improve with a tighter pin/bushing fit but then the shank won't move when played. Hence, 5 swings.
Now, when different materials are used, that goldilocks zone changes. With lower friction, the joint can be more rigid and still lower friction. The WN&G components exemplify this: the side play of the joint is unprecedentally minimal but friction is much lower than historic parts. The S&S PTFE treated bushings are somewhat in between. But it boils down to the reality that an adequately rigid joint can be achieved with a lower level of friction. That means that the "swing test" needs to be higher -- maybe 10 swings or more, in fact, whatever works that still retains joint rigidity for solid tone.
2) I and some others servicing high-level pianos have found ironing the bushing using the final-installed pin to be the most precise way of sizing the bushing. I just put in a pin that is tight (not to the point of immobilizing the joint, though) and before cutting it poke it into a torch flame. The heat irons the felt and leaves it smooth and dense. The advantages are these: a) nothing more accurately represents the final size of the hole to fit the pin than the pin itself. b) there is no disturbance of the felt, c) it works reliably and consistently. As with anything, it is possible to do it wrong. If your mind wanders, you can get a carbonized shank fork, for example. But it is quite easy to do it right.
3) There is a third factor that I didn't see in the discussion about heat and water on felt and that is mechanical agitation. I have a nice pair of mittens that a friend makes from sweaters she gets from thrift stores. She washes the sweaters in hot water and soap and they shrink and become dense -- making wonderful gloves. This is similar to the "boiled felt" gloves found in Europe. So felt is made from wool that is agitated in water. The addition of soap and heat and length of agitation time are what makes the felt more dense -- and that on a continuous scale until it becomes like ceramic. (I have actually seen a "tile" of wool that serves its owner as a kithchen trivet).
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Keith Akins
Akins Pianocraft
Menominee MI
715-775-0022
Original Message:
Sent: 12-27-2017 11:10
From: Alan Eder
Subject: teflon impregnated action center bushing cloth
Hi All,
The subject line would have been even longer if it included the problem (allegedly) encountered with same.
Steinway D, less than five years old. Original action parts manufactured by Steinway New York. Complaint was that the action was too light. (And this from a world-class pianist and highly sought-after teacher, who has much more knowledge about how the darn thing works than the do the vast majority of his peers.) Static Touch Weight measurements were not too far off (and the hammers were not too hard, which can contribute to the perception that the action is lighter), but key bushings and balance holes were too loose, as were 90% of the hammer flange action centers. Dealt with the keystick contact points. There was evidence that many of the hammer centers had already been repinned, and yet were still unacceptably loose. The technician who normally services this instrument confirmed that this was indeed the case. (Our normal working spec is five swings of the hammer when dropped from horizontal while holding the flange still at vertical, with the amount of friction on each side either identical or close to it.)
So, what I want to find out is this: Have others had the experience of repinning these kinds of parts (to reduce friction to similar, optimal condition), only to have them promptly loosen up again (and I don't mean a little, but to 10, 20, 30 and more swings)? We have repinned the hammer centers and were cautioned by someone with much more experience with these parts than I have that they will just loosen up all over again. Gosh, I sure hope those hours of repinning were not all for naught.
Alan
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Alan Eder, RPT
Herb Alpert School of Music
California Institute of the Arts
Valencia, CA
661.904.6483
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