[pianotech] Worn hammers breaking strings

[Don Mannino]

Claude,

 

The short and simple version:

 

Properly shaped hammers push up on the string with a curved profile which
(sort of) matches the natural curve that is formed in the wire by the shock.
The force of the hammer against the string pulls against the front
termination (agraffe / capo) and throws a nice big wave in the string
towards the bridge.  Within a few microseconds this shock wave settles down
into a relatively consistent vibration of the string throughout its length.
It is the initial pulling and bending up motion of the string that is most
stressful for the wire.

 

A flat topped hammer pushes up on the wire with a flat surface, which in
itself is harder on the wire.  Plus, the edge of that flat surface is closer
to the termination point.   This increases the stress on the wire because
the transfer of energy into the wire is not as efficient, because it too
close to the termination for proper "leverage" if you will.  The "yank" on
the string is sharper and harder, and from the hammers point of view the
string is less yielding.

 

Worn hammers in themselves do not cause string breakage, but tests have
shown that they clearly increase the metal fatigue in the wire at the
proximal termination.  The longer the string grooves are, the higher the
stress.

 

Don Mannino

 

From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Claude M. Harding
Sent: Saturday, January 29, 2011 10:23 AM
To: pianotech at ptg.org
Subject: [pianotech] Worn hammers breaking strings

 

Through the years I've heard, and sometimes repeated, the conventional
wisdom that says worn hammers are more likely to 

break strings.  I recently refrained from saying it again because I realized
that I really don't know why this may be true.

I'm not necessarily doubting it, but if it IS true, I would appreciate a
"Readers Digest"-version explanation of the physics involved,

 or the "address" where I could find such an explanation.

Help appreciated.

Claude Harding

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