Pinblock question

[Delwin D Fandrich]

----- Original Message -----
From: <ETomlinCF3@AOL.COM>
To: <pianotech@ptg.org>
Sent: Saturday, July 24, 1999 11:12 AM
Subject: Pinblock question


> List,
>
> ... I know it needs to be modified to allow a 7 degree angle ...
>
> Ed
>
--------------------------------------------------

Ed,

Before you drill this pinblock, let's think about this a bit.  Where did the
7º specification come from?  What is the rational for it?  I expect that
part of this might have originated with early 3-ply pinblocks that had a bit
more give in them than do modern multi-laminate pinblocks, but that is pure
speculation on my part.

There are no definitive specifications for tuning pin back angles on
 "modern" pianos.  It varies from one piano to the next.  And, although it's
rarely drilled this way, the correct pin angle may well vary within the
compass of a single piano.  That is, the correct angle may be different in
the bass section than it is in the tenor.  And may be yet some other angle
for the treble sections.  In other words, there are no absolute
specifications....

As far as the tuning pin is concerned it really doesn't matter what the
drilling angle is in the pinblock.  This is not a structural issue.  The pin
is not going to pull out of the block if the angle is too little.  And it's
not going to be more stable if it is extreme.  What does matter is the angle
that the string makes with the tuning pin.  The string should make a 90º to
92º angle with the centerline of the pin relative to the bottom of the pin.
That is the string should leave the pin at no less than 0º and no more than
2º from perpendicular to the centerline of the pin.  With the pin driven in
to its correct height and the string at pitch it should bear up very
slightly against the coil as the tuning pin is turned clockwise-as in
raising the pitch.  Remember, this applies to string tensions appropriate to
the modern piano.  Not harpsichords or even fortepianos.  I suspect that
greater angles probably wouldn't be as dangerous at the considerably lower
tensions found on these strings.

Boring for the tuning pins to achieve these angles depends on the plate
design and the string termination arrangement used.  And, of course, on the
diameter of the wire, the number of coils of wire on the pin, on how far the
pin is driven into the block, etc.

For example, through the tenor section of an unmodified Steinway B the
string may well leave the counterbearing felt just barely above the plate
surface-1 to 3 mm is not uncommon.  In this case the pin angle shouldn't be
much at all.  In fact it would probably be best to bore straight through
this section.  I've seen some pianos in which the pins really should have
been installed with something of a forward angle.  Moving to the treble
sections the string passes over a set of counterbearing bars that vary in
height along their length and that place the strings at some variable
distance above the plate.  But, overall, they will be somewhat higher than
they are in the tenor-about 3 to 6 mm.  Here the ideal tuning pin back angle
might be anywhere from about 1º to 3º.  Finally, depending on the height of
the bass counterbearing bar, the correct tuning pin back angle through the
bass section might be anywhere from 2º to 5º.  These angles are drawn from
memory but you get the idea.  For the most part we compromise and bore to
some average back angle that we anticipate will work reasonably well
throughout the scale.  Although in some cases I have varied the bore angle
from the bass to the tenor section.  Especially in vertical pianos with
fairly tall agraffe panels and very short string segments between
V-bar/agraffe and the tuning pin.

I frequently hear of pinblocks being drilled at what I consider to be both
extreme and excessive back angles -- 5º to 7º, occasionally even more.  What
the purpose of this is in the modern piano, I don't know.  If the back angle
is excessive the string will work its way down the pin as the piano is tuned
and the technician will be faced with a constant -- and losing -- struggle
to keep the coils tight.

So, for the modern piano at least, we have to look to the string angle
relative to the tuning pin to tell us what the bore angle for the tuning pin
should be and not just rely on some arbitrary standard we may have heard
about.

Regards,

Del