<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META http-equiv=Content-Type content="text/html; =
charset=iso-8859-1">
<META content="MSHTML 5.50.4134.600" name=GENERATOR>
<STYLE></STYLE>
</HEAD>
<BODY bgColor=#ffffff>
<DIV><FONT color=#000080></FONT> </DIV>
<BLOCKQUOTE dir=ltr
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; =
BORDER-LEFT: #000080 2px solid; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: =
black"><B>From:</B>
<A title=caute@optusnet.com.au =
href="mailto:caute@optusnet.com.au">Tony
Caught</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A =
title=pianotech@ptg.org
href="mailto:pianotech@ptg.org">Pianotech</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> September 21, 2002 7:43 =
PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: hammer felt =
(Renner
Blues)</DIV>
<DIV><BR></DIV>
<DIV>Dave,</DIV>
<DIV> </DIV>
<DIV>You wrote</DIV>
<DIV> </DIV>
<DIV>
<DIV><FONT size=2>The importance of the staple is somewhat
controversial. There are those who argue that it adds tension to =
the
lower part of the hammer and those who say it doesn't make any
difference. The Renner blue is, of course, without a =
staple.
</FONT></DIV></DIV>
<DIV> </DIV>
<DIV>Not having a staple would mean that you cannot use this =
hammer in
high humidity conditions. However,</DIV>
<DIV>As the hammer absorbs moisture from the air, the tension created =
varies
greatly as does the tone. Possibly being not stapled would allow this =
increase
of tension to spread more evenly over the hammer and not be restricted =
by the
staple.</DIV>
<DIV> </DIV>
<DIV>Tony Caught<BR><A
=
href="mailto:caute@optusnet.com.au">caute@optusnet.com.au</A></DIV></BL=
OCKQUOTE>
<DIV dir=ltr><FONT color=#000080></FONT> </DIV>
<DIV dir=ltr><FONT color=#000080></FONT> </DIV>
<DIV dir=ltr><FONT color=#000080>Tony, et al.,</FONT></DIV>
<DIV dir=ltr><FONT color=#000080></FONT> </DIV>
<DIV dir=ltr><FONT color=#000080>In general the staple is an =
insurance policy
against a variety of gluing problems. In the early days of piano =
building, of
course, animal hide glue was the only adhesive available to =
bond hammer
felt to the wood molding. Whatever its other merits, animal hide glue =
was (is)
particularly unsuited to this task--it goes on hot and, as the felt is =
pressed
against the wood molding, much of the water solvent migrates into the =
wool felt.
This leaves the glue too dry to form a reliable bond.</FONT></DIV>
<DIV dir=ltr><FONT color=#000080></FONT> </DIV>
<DIV dir=ltr><FONT color=#000080>Something needed to be done to =
retard this
water migration, hence the various shoulder treatments that ultimately =
came to
be called hammer reinforcing or shoulder hardening solutions came into =
use.
Despite their names, none of these solutions did much to reinforce =
anything and
they were not intended to harden the working end of the hammer at =
all. They
were designed to retard the rate at which the water solvent component
of hide glue migrated into the felt and, hence, help prevent =
starving
the glue joint. A starved glue joint between the felt and the wood =
molding
results in a fairly weak bond and is susceptible to early =
failure--especially
under varying stress loads. </FONT></DIV>
<DIV dir=ltr><FONT color=#000080></FONT> </DIV>
<DIV dir=ltr><FONT color=#000080>Like wood, wool felt expands and =
contracts with
variations in moisture content creating physical changes in the felt =
that do
continuously vary the stress loads on the felt-to-wood glue joint and =
that lead
to its rapid breakdown and failure. Under these conditions the staple =
does help
to stabilize things--enough, at least, to prevent most felt-to-wood =
bonding
failure. </FONT></DIV>
<DIV dir=ltr><FONT color=#000080></FONT> </DIV>
<DIV dir=ltr><FONT color=#000080>Most of the adhesives used to bond =
hammer felt
to the wood molding today do not have this problem, or the problem can =
be
controlled in other ways. </FONT></DIV>
<DIV dir=ltr><FONT color=#000080></FONT> </DIV>
<DIV dir=ltr><FONT color=#000080>One way is to raise the moisture =
content of the
felt to the point at which the water solvent in the glue is not so =
readily drawn
into the felt. An unfortunate side effect of this process is that when =
the
hammer felt is pressed into a heated caul--as is typical of nearly all =
hammer
makers today except for Isaacs and Ronsen (are there others?)--the felt =
takes on
a rather permanent set much like your wrinkled wool slacks do when they =
are
steam pressed at the cleaners. This pressing process results in the much =
more
dense and less resilient hammer that we all know and love to voice.
</FONT></DIV>
<DIV dir=ltr><FONT color=#000080></FONT> </DIV>
<DIV dir=ltr><FONT color=#000080>Even today not all of the adhesives =
used to
bond hammer felt to wood moldings are completely waterproof after they =
are
cured. For a variety of reasons some hammermakers use one of several
thermoplastic adhesives similar to commercial PVAs (white glue) and/or =
aliphatic
resins (yellow glue). These adhesives are generally moisture resistant =
but can
fail if exposed to very high humidity levels. With these adhesives the =
reasons
for failure are different than those encountered with animal hide glues, =
but the
point of failure and the type of failure is the same. In these hammers =
the
staple is probably an essential structural component. If the adhesive is =
rated
as 100% water/moisture resistant--and if it is properly handled and =
applied--the
staple is not necessary for structural purposes. </FONT></DIV>
<DIV dir=ltr><FONT color=#000080></FONT> </DIV>
<DIV dir=ltr><FONT color=#000080>It is debatable as to whether the =
staple is
desirable--or at all effective--at promoting, enhancing or stabilizing =
tone.
Generally the staples are inserted below the parting line of the hammer =
caul and
well below the point at which the trimming knife has cut deeply into the =
continuity of the outer layers of felt. Personally, I don't see how a =
staple of
any variety can do much to support the functioning portion of the hammer =
from
down there, though I'm willing to be convinced. (I will say, =
though, that
I've taken out enough hammer staples and have tried--unsuccessfully--to =
hear any
resulting tonal differences to be some skeptical.)</FONT></DIV>
<DIV dir=ltr><FONT color=#000080></FONT> </DIV>
<DIV dir=ltr><FONT color=#000080>Nor do I see how staples of =
different types are
going to function differently, assuming each is installed correctly. Ron =
has
described the different types in one of his posts and I have found =
problems with
each. The two types of through staples are very often loose (especially =
the
<EM>T-types</EM>), obviously supporting nothing but themselves and =
hardly that.
The U-shaped staples are driven in with an air hammer and come in a =
variety of
lengths. These lengths must be carefully selected to extend through the =
shoulder
felt and into the wood molding. Many of these staples are coated with a
thermo-activated adhesive--the adhesive is heated by friction as the =
staple is
driven home--and once it enters the wood molding some reasonable =
distance it is
structurally and permanently secure. It is desirable that the staple not =
extend
all the way through the molding. Now, look at the side of a hammer and =
consider
how the staple is inserted and you'll quickly see how tricky it can be =
to get
this just right. Being just a bit heavy or light with the trimming knife =
or
slightly high or low on the shoulder from your desired insertion point =
can make
quite a difference in how far the staple penetrates the molding. As =
well, the
staples only come in a limited variety of lengths. Three or four lengths =
will be
used on one set of hammers.</FONT></DIV>
<DIV dir=ltr><FONT color=#000080></FONT> </DIV>
<DIV dir=ltr><FONT color=#000080>Given some time I could probably =
think of a few
more things to say about hammer staples. But I suspect I've all ready =
tossed out
enough stuff to generally confuse things.</FONT></DIV>
<DIV dir=ltr><FONT color=#000080></FONT> </DIV>
<DIV dir=ltr><FONT color=#000080>Regards,</FONT></DIV>
<DIV dir=ltr><FONT color=#000080></FONT> </DIV>
<DIV dir=ltr><FONT color=#000080>Del</FONT></DIV>
<DIV dir=ltr><FONT color=#000080></FONT> </DIV>
<DIV dir=ltr><FONT color=#000080></FONT> </DIV></BODY></HTML>