High Density Pinblocks

[Delwin D Fandrich]

----- Original Message -----
From: Ron Nossaman <RNossaman@KSCABLE.com>
To: <pianotech@ptg.org>
Sent: March 08, 2000 6:54 AM
Subject: Re: Baldwin torque, (was survey)


> The reported reason for using the infinite layered pinblock is that it
> isn't as prone to degradation through the years because it doesn't react
> much to humidity changes. By my experience, it does react quite obviously.
> Given the fact that there is very little resilience to the material, that
> is very little recovery or spring back from compression, the torque
> readings from low to high humidity periods will be substantially different
> even though the block dimensions don't change much. Even so, they seem to
> age relatively well, generally, but you will find the individual loose pin
> more often than in less dense blocks. At least that's what I have found.
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Ron, et al,

The process used by Baldwin to make their grand piano pinblocks is a
slightly modified version of one developed during the 1940's to make a
resin-treated compressed wood product known as "Compreg" - or "compressed,
impregnated wood.  A paper written for the U.S. Dept. of Agriculture by the
Forest Products Laboratory in 1951 discussed the development of this process
and the characteristics of wood based products made in this manner.  This
material was originally developed to form the engine mounts (stringers)
found in wood hulled mine sweepers.  Being non-magnetic, it would not
trigger mines designed to detonate in the presence of ferrous metals. It had
the advantage of being both harder and somewhat more reliable than brass in
this application.

Compreg is a treated wood product that is made of wood and resin-forming
chemicals (typically phenol- or resorcinol-formaldehyde) that act as
plasticizers for the wood so that it can be compressed under high pressure
to a specific gravity of 1.0 to 1.4.  Several different resins were tried
while the process was being developed, but the most successful was, and
still is, water-soluble phenol-formaldehyde resin.

In making Compreg, wood veneers are treated with water-soluble
phenol-formaldehyde to a level that will result in a resin content of 25 to
30 percent based on the ovendry weight of the wood.  The resin is allowed to
dry without curing at temperatures below 30º C (approx. 175º F).  The resin
is actually cured later on during the heating and densification
(compression) process.  Panels are made by stacking treated veneers of the
required thickness and quantity in a hydraulic press, then heating and
compressing them to a specific gravity of approximately 1 to 1.4.  In the
original Compreg process, temperatures of 150º C (300º F) and pressures of
1,000 to 1,200 lbs/in2 (70 to 85 kg/cm2) were used.

The Baldwin process uses similar temperatures -- this is required to cure
the adhesive -- but lower pressures, hence, the density of the Baldwin
pinblock is somewhat lower than the maximum that the process is capable of,
but it is still quite high.  (By the way, with some variation in detail,
similar processes are used to make Delignet and Falconwood blocks.
Falconwood being the more dense of the two, if memory serves.  In these
products beech is used instead of maple, but the adhesives are similar as
are the temperatures and pressures.)

The resulting material is well on its way to being a fiber-reinforced
plastic (FRP) and has several characteristics more like those of FRP
products than of wood.  Indeed, with the exception that kraft paper is used
instead of maple veneer, this is nearly the same process that is used to
make Formica and other such "plastic laminates".

Compreg does have certain characteristics which would seem to make it a good
material for piano pinblocks:
 1) It is very stable when subjected to humidity and temperature cycles.
 2) It resists cracking and splitting.
 3) It has high compression strength.

It was probably these characteristics that led Baldwin and other to use
these materials in the first place.  Unfortunately, it has several other
characteristics that make it unsuitable for use as a piano pinblock
material:
 1)  Springback (after compression), or resiliency, is very low.
     - A material with low springback will simply deform when compressed.
     - When the tuning pin is driven into the pinblock it compresses the
wood and depends
        on the woods ability to "springback" to hold it tight and maintain
good, consistent
        tuning pin torque.
 2)  Hardness is 10 to 20 times that of normal wood.
 3)  Impact strength ("toughness") is about 1/3 to 3/4 that of normal wood,
but this is very
      susceptible to the variables of manufacture.
     - The impact strength of the pinblock material is the quality that
prevents the pinblock
        from being damaged while the pin is being driven into the tuning pin
hole.
     - The reduced impact strength, or toughness, of Compreg allows the
pinblock to be
       easily damaged as the piano is being strung.
 4)  Machinability is decreased.  True Compreg takes on some of the
characteristics of
      metal and in some cases requires metal working tools for machining
operations.
 5)  It is possible to burnish material to a very smooth, glossy surface.
     - This is the characteristic that leads to "jumpy" pins in pinblocks
made with these
        materials after several years in use.

Obviously these materials can be used to make piano pinblocks.  As the
density of the material goes up, however, so do the potential problems.
They become more critical to variations in manufacture.  Slight variations
in hole diameter that would be insignificant in a more resilient material
become critical in these blocks.  The difference between a loose set of pins
and a tight set is slight indeed.  Pianos that leave the factory with
relatively consistent pin torque can develop random loose pins over
relatively brief periods of time.

(By the way, the reason you don't have these problems with Baldwin vertical
pianos is that they are built differently.  The traditional high-density
Baldwin grand piano pinblock is fairly expensive to manufacture.  Much to
expensive to put in the more mass-produced verticals.  Consequently, the
verticals actually have a much better pinblock.  At least in my opinion.)

This is probably more than you ever wanted to know about this stuff.

Regards,

Del.

PS
The above is from a work I have written for future publication.  Hence the
notice below:
Copyright (C) 2000  This material may not be copied or reproduced in any
form without the authors permission.