BACK POSTS AND
FRAME CONSTRUCTION:
The strength of the
piano structure is very important to help control
tuning stability. Each string (about 230 strings in a
piano) has up to 180 pounds of tension. This amounts
to approximately 20 tons of tension or the combined
weight of 9 (nine) full size automobiles when the
piano is in tune. The tension must be supported by
the back frame construction (a combination of the
metal plate and back posts). The stronger the back
frame, the longer the piano will stay in tune.
THE METAL PLATE:
Plate should be
what is know as "full cast plate made of gray
iron and showing the name of the piano manufacturer
cast therein. Finish should be either bronze or
silver. The tension must be supported by the back
frame construction (a combination of the metal plate
and back posts). The stronger the back frame, the
longer the piano will stay in tune. There are many
fine European and American pianos that have no back
posts at all. This is because they place an emphasis
on the strength of an extra heavy I-Beam like plates.
Both methods are excellent.
REMINDERS:
1. A piano is a
stringed instrument.
2. Strings are pulled to high tension.
3. The back posts and the cast iron plate work in
concert to support the tremendous tension of the
strings.
4. Reasons why it is necessary to have the strongest
structure possible to support string tension:
* To prevent
the back of the piano from warping and twisting.
* To enable the piano to stay reliably in tune
between tunings.
* Without solidity in the structure the many parts of
the piano could not function properly.
THE BACK POSTS:
1. Look at the
back of the piano first, the back posts are easy
to see on most instruments. Notice the
following things about the back posts:
* Size of
the post; not only width, but depth.
* Double, triple, posts - wood grain appearance
* Post extend to the top of the piano.
* Posts extends to the bottom in a tight tenon
and mortise constructon. Feel with fingers.
MATERIAL USED
IN BACK POSTS - SOLID SPRUCE:
* Because its
the strongest wood for it's weight.
* Resists splitting and cracking.
* Spruce's lengthwise grains are straight,
close and dense which provides rigid support.
* Posts are bolted to cast iron plate.
EXCEPTION TO
THE RULE:
As mentioned,
some
pianos will have metal back posts, others, will have
virtually no wood back posts at all. Many high quality
pianos have scale designs which provide plates that
have rigid I - Beam like construction that extend to
all four corners of the frame, which actually adds
the strength of two or more back posts. This is an
expensive process known as a full perimeter plate.
This is an acceptable method.
TUNING
PINS AND PIN BLOCK
1. The purpose of
the pin block is to firmly hold the tuning pins in
place where the strings are attached.
* Tuning
pins vary in quality.
* Better grades of tuning pins have machine cut
threads.
* Tuning pins should be "blued steel",
an electronic method to prevent rust.
* Nickel-plated steel tuning pin.
2. The pin block
in many of the finest pianos in the world
consists of several plies of hard rock maple.
Alternate plies have grain running at ninety
degrees to that of adjoining plies to assure even
gripping of the pins, and to prevent splitting of
the pin block.
* Material
of pin block should be hard rock maple.
* Wood should be quarter sawn for strength.
* Pin block should be at least 2" thick.
* Number of plies not as important as type and
cut of wood.
