Open face vs. closed face pin blocks

[Phillip L Ford]

Del,
Not to belabor this but something about your earlier post occurred to me
later.  The excerpt from your post is below.  I was so focused on energy
loss, yada-yada, that I hadn't noticed what the numbers I had generated
said about pitch raising and stabilizing.


On Wed, 15 Aug 2001 09:36:41  
 Delwin D Fandrich wrote:

>While I personally don't have enough experience tuning pianos with open-face
>pinblocks to give any kind of definitive answer on their long-term
>stability, I can say that they are certainly easier to tune. They
>pitch-raise easily and stabilize quickly.
>
----
Here are the calcs again:

Assume:

  Iron  E   = 18,000,000 PSI
  Steel E  = 29,000,000 PSI
  Maple E = 1,800,000 PSI

  Tuning pins are .282 inch diameter

  Assume a unit load of 100,000 lbs - I know this isn't a real load, I'm just
       using this for a basis of comparison and to keep my deflections from
       being so small (too many zeros to the right of the decimal point).

  For a tuning pin with string coming off .25 inch above pinblock, deflection of
  the string in the direction of load is 0.014 inch

  For a tuning pin with string coming off .50 inch above pinblock, deflection of
  the string is 0.112 inch

  Assume a plate with an unsupported span (span between plate struts) of
  18 inch.  Assume the total width (parallel to the string) of the plate in the
  pinblock area is 8 inch.  Assume the plate and pinblock act as a fixed ended
  beam between the plate struts.

  For the open plate pinblock:
  Assume plate flange is 1 inch deep and 3 inches wide.  Pinblock is 5 inches
  wide and 1.5 inch deep.  Deflection at center of beam for 100,000 lb load
  is 0.044 inch.

  For the closed plate pinblock:
  Assume front and rear plate flange are 1.5 square inch in area.  Assume
  pinblock is 7.5 inch wide and 1.375 inch deep.  Deflection at center of 
  beam for 100,000 lb load is 0.0048 inch.

----
Now notice for the closed face pinblock system total deflection of pinblock
and tuning pin are 0.112 + 0.0048 = 0.117 inch

For the open face pinblock system total deflection of pinblock and tuning
pin are 0.014 + 0.044 = 0.058 inch

Now for the actual string load of 150 lb (or whatever tension you choose
to use) the actual numbers will be smaller.  But the point is that for the
closed face system the applied load on the string causes it to move
TWICE as much as the same string on the open face system.  And this
is assuming a tuning pin height for closed face system of twice that of the
open face system.  As Paul has pointed out it is often more, in which case
these deflection differences would be even more pronounced.  No wonder
that the open face pinblock pianos pitch raise easier and stabilize quicker.

Phil

---
Phillip Ford
Piano Service & Restoration
1777 Yosemite Ave
San Francisco, CA  94124




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