Hammer weight/density

[Delwin D Fandrich]

----- Original Message -----
From: "Joseph Garrett" <joegarrett@earthlink.net>
To: <pianotech@ptg.org>
Sent: October 15, 2001 7:10 PM
Subject: Hammer weight/density


> Del,
> You stated that the pound designations really are meaningless and I agree.
> Is there a meaningful way of measuring the density? I have seen "Density
> Meters", (my description), designed for measuring the density of metal.
Are
> these a viable means of measuring something as soft as felt? Inquiring
minds
> want to know.
> Best Regards,
> Joe Garrett, (Oregon)
> -------------------------------------------------

None that I am aware of. Baldwin (and probably others) used a durometer to
test the felt sheets before cutting and pressing hammer sets, but this was
not really very useful. It measured the hardness of the surface of the sheet
of felt as it came from the felt maker, but this told us very little about
how finished hammers made from this felt would perform--there are just too
many variables in the hammermaking process.

I'm not really all that interested in just a hammer's weight or density all
by itself. What I would really like to see is a method of rating a hammer's
resilience--that is, it's ability to deform on striking something like a
piano string and then to recover from that deformity. This, combined with a
general ranking of the actual weight of the finished set of hammers, would
at least get us in the ballpark of being able to predict their performance.

The actual rating system wouldn't have to be elaborate; perhaps just a mass
rating of light, medium and heavy coupled with a resilience rating of low,
medium and high. That would give us nine choices and the ability to match
hammers to just about any piano made. Getting there could be some difficult,
however.

To be meaningful a rating system will have to consider the rate of energy
transfer over time as measured by some standardized test blow against some
standardized energy absorber. Coming up with an appropriate test mechanism
is not going to be easy. And then, once the test mechanism is developed, how
are we going to use it? Are we going to check just one hammer out of a set?
Or several? Do we check each set? Or do we trust the manufacturer to test
samples and label them accordingly? As you can see, this could quickly get
complex and expensive. Some years ago I worked on this problem just enough
to learn that it was going to take a lot more time and effort that I could
devote to it at the time.

The problem will be coming up with that resilience ranking--bearing in mind
that soft and resilient are not the same thing. Consider that dropped
against a hard surface from some given height both a golf ball and a 'super
ball' will bounce quite well but one is very hard and the other is rather
soft. And I don't even want to think about 'silly putty.' Marshmallows are
soft but they don't regain their shape after being deformed. Foam rubber is
also soft but bounces back quite well after being deformed.

As may be, one way might be to clamp a test hammer in a fixture with the
hammer's tail resting against a solid and massive surface. A striker of
known shape, mass and velocity could be dropped against the strike point of
the hammer and its rebound characteristic measured. I'm not sure if the
result would tell us enough about the performance potential of the hammer,
but this would be a fairly easy place to start.

Another way might be a mechanism which would easily and quickly clamp a test
hammer and then accelerate it to some standardized velocity. The hammer
would impact against a standardized length of string set at a standardized
pitch. An accelerometer would measure the impact and, using the signal
generated by the accelerometer, we could come up with some way to rate the
hammer's performance.

As I said, it might not be easy.

Del