hammers

[Delwin D Fandrich]

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  ----- Original Message -----=20
  From: Dave Nereson=20
  To: Pianotech=20
  Sent: June 02, 2003 2:03 AM
  Subject: Re: hammers




        What??  The Steinways I've seen have always had an egg-shaped =
hammer.  Aren't we sposeta file trying to remove only one layer of felt, =
or enough to remove the string grooves, without changing the shape of =
the whole hammer (unless it's a grossly misshapen mess due to someone =
else's botch job)? =20

Back in the "good old days" the basic hammer shape was formed primarily =
in the caul, not on the sanding machine. This is now longer the case =
with many modern hammer makers.

Because of the way the felt sheets were (are?) laid up the hammers used =
on early pianos, including Steinways, did retain their original =
as-pressed shape through the sanding process. It was possible to pick up =
and file off just one or two layers of felt--indeed, for best =
performance it was necessary to file hammers this way.=20

The felt used to make hammers--at least in the US--starts out as a very =
wide and long continuous loop of loose wool looking something like a =
diaphanous, or gauzy, conveyor belt. Once the loop is formed it is built =
up by adding more and more loose wool in distinct layers until the =
desired thickness and taper is obtained. Once the belt is built up to =
its desired thickness and taper it is cut up into large sheets of =
appropriate size and felted. During the felting process these individual =
sheets will compress quite a lot coming out approximately the final =
desired size, taper and weight. They are then cut to size and shipped to =
the hammermaker. The hammermaker will then cut these sheets into tapered =
strips appropriate to the size, weight and shape of hammer to be =
pressed.

As long as animal hide glue was used to bond the felt to the wood hammer =
molding all hammers were cold-pressed. It wasn't until well after =
thermal-setting adhesives (mostly phenol-formaldehyde) were developed =
that heated cauls came into being. (And this for faster press cycles, =
not because it resulted in better hammers.) Even after pressing there =
remained in these hammers definite density gradations between distinct =
layers that could (can) be picked up and followed by the careful voicer. =
I have encountered some of these hammers with such well defined layers =
it was very nearly possible to raise up a single layer and peel it off =
the outer perimeter without using a sandpaper file.

It was the combination of this felting process combined with the cold =
press, the properly shaped press caul, the properly cut hammer strip and =
probably a hundred other details that gave these hammers their wonderful =
resilience and tone qualities. Steinway still uses a similar felt but =
for reasons of their own now seems to find it necessary to heavily sand =
their hammers to shape. Whether this is because the desired shape has =
changed or because the shape of the cauls or the shape of the hammer =
strip has changed, I do not know. What I do know is that when using this =
process to make hammers it is vital that you not sand through the =
individual layers on the shoulders of the hammers and leave those over =
the crown unsupported. When this happens the felt around the crown loses =
its foundation and quickly loosens up, acting then as a damper between =
the string and those deeper under-layers that are still under =
considerable tension. Once this happens piano tone goes dead and out =
comes the lacquer. But those hammers will never sound the same again.

With what I call hard-pressed hammers, i.e., those pressed with =
relatively damp felt under relatively high pressures and using highly =
heated cauls, any layering that might have been present in the original =
felt tends to disappear. It's kind of like steam pressing your wool =
slacks. The wrinkles disappear under the combination of heat, steam and =
pressure. The wool fibers are literally reformed and take on a much more =
homogenous mass. With these hammers it doesn't seem to matter much if =
they are filed to shape or pressed to shape. You can cut across the =
grain line with impunity and not worry overly much about what will =
happen.

Del


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