Work Hardening (was: Hammers with no inner felt)

[Bill Ballard]

At 4:16 AM -0400 7/26/02, Erwinspiano@AOL.COM wrote:
>      I meant to comment on the "work hardening" idea you stated last 
>week.  I have an idea what you >refer to but as I see it all hammers 
>soft or hard have some work hardening done to them as they >develop 
>string marks, compacting right on and barely under the strike 
>surface. The results are quite >different depending on the hammer. 
>If I understand you term or concept this is what this means.

You're right on. The meeting of Society for the Promotion of 
Work-Hardening as a Concept is now called to order.

>  Basically two springs pushing on each other rather than a head on 
>collision If this is somewhat clear the >next part should fall into 
>place.

I've used this description as well.

>   Work hardening and the subsequent development of some kind of 
>molecular change in the felt >beneficial to tone is only possible if 
>the hammer has a certain amount of stiffness or limited 
>resilience >to begin with. With unlimited resilience (too soft) the 
>hammer no longer works as a nonlinear felt spring >and cannot take 
>advantage of work stiffening/hardening. It is too linear, unable to 
>get progressively >stiffer with increasing levels of energy applied, 
>it becomes instead more of a damper. >Hardeners/stiffeners 
>(lacquers) must be applied to limit resilience then work hardening 
>can apply.

Agreed, which is why I went at this set of one-year-old NY Steinway 
hammers with the reinforcer. The first season, I had stayed out of 
the crown on the assumption that I'd prefer to see what could be 
gained if the sole factor was work-hardening (no reinforcing 
involved). It was a great sounding piano, but with no projection. And 
work hardening was not advancing the tone because of the softness of 
the crown. There was simply too much compression needed; work 
hardening might accomplish it, however over a couple of years of 
play. This piano sees two months of solid play per year. I didn't 
have the time to wait for that process.

>     For the overly plasticized or (petrified felt) hammer work 
>stiffening happens at the immediate >surface only compacting surface 
>felt seen as the string grooves which cause a nasty sound we 
>all >dislike, but does nothing else except annoy & assault piano 
>tuners ears. Not much musical dynamics to >be had here.

If the air space has been filled in with solid resins, there's 
nowhere for the felt mass to squash. The same is true of the 
hot-pressed felt whose matte of fibers has been thermoplastically 
reset to replace the air space with the adjacent fibers.

>    However for the hammer with a reasonable amounts of 
>reselience/stiffness, meaning not too much >needling or juicing to 
>get close to desired piano tone, work hardening is something that 
>happens not only >in the string grooves but deeper underneath and 
>thru out. The felt takes on a set but doesn't freeze up. >Sometimes 
>it shows up visually like the hammers have taken this set, squashed 
>a bit on the top and out >at the shoulders. I've seen this in 
>Isaac,Ronsen and Stwy hammers.  Primarily though it shows itself 
>in >the tone which is what I your point was Bill. The tonal 
>ripening.   Hmm I like that Bill

The other thing I would include in work-hardening is the way the 
fiber hook their platelets together during this compacting. This 
means that the fibers, having been elastically deformed during the 
hammer blow, become locked together by the action of the platelets in 
this increased level of elasticity. Air space (which in quantities 
too large, produce only a damper) is now replaced with increased 
resilience. BTW, density has also increased.

>       The more the felts resilience is stolen during pressing the 
>less likely work hardening has any effect >or validity to its tone 
>production qualities.

Hot-press a strip of hammer felt to bend it around a moulding in a 
press, and the elasticity of that bending is thernmoplastically 
released, resulting in a felt mass nicely bent around the molding 
(without tearing) but starting out in this position with little or no 
resilience. The felt mass may have the airspace required for the 
"magic of work-hardening" to happen, but it's resilience has gone 
directly back to GO without collecting the $200 worth of extra 
resilience.  (Did the terminology just get monopolized?)

Dale, thank you for laying out what you thought I meant, which is 
exactly what I meant! I'd still like to try to define what changes in 
the first few years to turn a good piano into a great one. The 
external process of the ole' one-two punch with the pianist 
exercising the piano and the technician reliving the resultant 
hardening of the tone is one known essential part in this process. 
The internal ones, I know less about. Work-hardening (where the 
quality of the hammer allows it) is a process in the hammers. A year 
ago, you spoke of an A whose new board didn't sound like much after 
the initial stringing and action regulation with new hammers. It was 
on its side in your shop for (six months? a year?), and when you set 
it up again, it sounded like heaven, just the way you were initially 
wishing it to sound. What's at work here? Whatever it is, I'd at 
least say that the board is undergoing its own internal processes.

Pianos are like new born human beings. Full maturity requires 
constant nurturing.

(Dang, just made myself another bowl of computer-fried oatmeal!@##@!)