>To all Hammer Heads
> In the previous thread I was trying to convey the way I see that a
> hammer
>is made & if you followed that then you see that I have a definition of
>tensioned felt in mind. However what I failed to articulate clearly is
>that Tension
>& compression go hand in hand in the hammer pressing process.
> As I stated, & piano hammer makers can tell you, that too much tension
> can
>be achieved during pressing in the outer layers of felt and it can & will rip
>open in the crown. This is the elastic limit of the felt. As the stretching
>of the felt on the outer perimeter happens the inner parts of the felt are
>compressing. It has too because of the stretching of the outer felt, the
>triangular shape the felt strip is cut & the hammer press pressure itself.
> ...
> Regards
> Dale Erwin
And in a previous post I was trying to convey the idea that the
makeup of the felt itself is important, and that perhaps the makeup of the
felt that is available now is different from what it was in the good
American hammers of the past. The old hammers look and feel different than
new hammers. It's hard to know how much of this is different felt and how
much is just age. Also, as TP pointed out, if you file these hammers
you'll often find embedded dirt and junk in the felt. Stick a needle in
one, and you'll sense that it feels different to the needle than a new
hammer would. You can push the needle in without much effort, and I have
the sense that the felt isn't really very dense. The felt seems to feel a
little 'grittier' for lack of a better term. And they respond dramatically
to even a single needle stitch. Also, you'll hear people referring to
layers in hammer felt when talking about new hammers. My experience is
that new hammers don't really have them. I haven't tried the new Wurzen
felt hammers yet, but I have tried the slightly older Wurzen felt
hammers(such is used on Hamburg Steinway I believe), and while the
impression of layering is more noticeable with these hammers, it's nothing
like it was in the old hammers. There really were layers, or at least they
behaved as if there were layers. You could peel one of those hammers like
a grape, if you were so inclined. This is all to say that I'm not sure any
felt available now is like the felt they were using a few decades ago, for
better or worse, and what I'm hearing here is that many people think it's
for the worse.
The discussion seems to concentrate on how hammers are made: hot or
cold pressed, lots of pressure or not, glue at the tip of the molding or
not, etc. There doesn't seem to be much discussion of the makeup of the
felt itself, other than is it Wurzen or not. I get the impression that
people think that sheep are sheep and felt is felt (the way that most
people think apples are apples - if you asked most people how many
varieties of apples exist, they would say two; red delicious and granny
smith. They would be astonished to learn that there are hundreds of
varieties of apples - we don't see any of them because of the nature of
business in this country, not because of the nature of apples). There are
many breeds of sheep. They produce wool of different colors, fiber length,
fiber strength, and felting ability. Also, sheep are not the only animals
that produce feltable fibers. Camels, goats, and llamas, among others also
produce feltable fibers with properties different from those of sheep wool
fibers. There's nothing to prevent these various fibers from being blended
with one another (I believe I heard Ari Isaac once mention that he wanted
to try making some hammers with felt that had some mohair in the blend). I
believe that the length and quality of the fibers depends on where on the
animal the wool comes from. I think the best wool is from the chest area
(but don't quote me on that). I can also imagine that the quality of the
wool from a given breed of sheep could be dependent on its sex, its diet,
and its environment. The wool from a male merino sheep eating grass in the
north of Scotland is probably going to be different from that of a female
merino sheep eating soybeans in California. So, there are many choices
available when making a selection of fibers to be felted.
After you choose your fibers you have to card them, clean them, and
perhaps bleach them. I don't know much about these processes, but I would
imagine that agressive or excessive carding could break down long fibers,
that excessive washing or washing with agressive soaps could strip
desirable substances off the fibers, and that bleaching could affect the
properties of the fibers (although all of these processes, agressively done,
would probably make the felt look nice and clean). So, more choices to make
about how to treat your raw materials.
Now you have your processed fibers and need to felt them. I'm not
clear on how they do this, but pressure, rolling, and perhaps heat are
involved. Once again, choices about how much pressure, how much rolling
and turning, and whether to use heat and how much.
So, there are many choices to make in each step of the process. Each
of these choices will affect the properties of the final
product. Unfortunately for us, I think that the felt properties that would
make the best piano hammers are not the felt properties that most
industrial customers are looking for. Wool that will make a good machine
tool vibration isolation pad isn't necessarily the same wool that will make
a good piano hammer. And piano hammers make up a tiny percentage of the
felt market. When I was at the Steinway factory I saw stacks of felt for
hammers. It looked like a lot of felt to me, but was apparently
insignificant to the supplier. I was told that basically Steinway has
to choose one of the suppliers standard felts because the amount of felt
they buy is a miniscule percentage of that makers output, and that the
maker wouldn't be bothered to make felt to their specifications for what he
considers such a tiny quantity. So, if we're getting hammers with dense
felt without much tension and compression in them, then that may be because
the hammer maker is working with the only materials available to him.
If a hammer having lots of tension and compression built into it by
the pressing is what gives a superior performing hammer, then you have to
have felt that is capable of standing up to that process. The outer fibers
have to be able to stand the tension. So, your felt has to be made up of
fibers of the requisite length and strength to achieve this tensile
strength. How the density of the felt would affect the pressing process is
unclear to me. But it seems possible to me that very dense felt might have
a different neutral bending axis, so to speak, as it's being bent over the
tip of the molding, which results in less tension on the outer fibers when
the hammer is pressed. This would be a desirable thing if you're using
felt without much tensile strength - perhaps another reason for using high
density felt. But if this supposition is correct, then to achieve high
tension in the outer fibers when pressing the hammer, you might have to use
lower density felt.
To make an old style hammer I think maybe you want wool with long
fibers that hasn't been manipulated too much and not pressed too hard. To
get the best felt for this purpose, let's imagine that you need chest wool
of a Lincoln sheep raised in a cold climate, not carded or washed too much,
not bleached, blended with some mohair, and felted to a low density. Can
you imagine anyone in the world being willing or able to supply such a
thing in 2004? Forget it. In 1904, probably. But we've made 100 years of
'progress' since then.
Phil
Phillip Ford
Piano Service and Restoration
San Francisco, CA
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