Old Upright, partial plate, Pitch?

[Delwin D Fandrich]

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  ----- Original Message -----=20
  From: Mike and Jane Spalding=20
  To: pianotech@ptg.org=20
  Sent: August 08, 2001 9:49 AM
  Subject: Old Upright, partial plate, Pitch?


  List,

  What about this exposed pinblock - are there unique problems and =
dangers associated with this thing? =20
Oh, this one might be interesting... Since this is a subject dear to my =
heart, here goes the first salvo:

In my experience the so-called three-quarter plate, exposed pinblock =
designs give no more trouble than do any others having the more common =
and traditional full plate configuration. Try as I might I've not been =
able to figure out why we regard these pianos as somehow structurally =
deficient.=20

There is really very little torsional stress--relatively speaking--on =
the pinblocks of the traditional upright piano regardless of its plate =
design. So, why do some of them fail? Well, consider how the pinblock is =
glued to the back assembly. Typically there will be five vertical wood =
posts--the back posts--separated by (usually) solid blockers. The grain =
of the posts is, of course, vertical. The grain of the blockers is =
typically horizontal. Now to this is glued a pinblock of varied =
construction. Some of them were multi-ply laminates much like the =
so-called modern pinblock. Some were made of relatively thick solids =
much like the traditional Steinway blocks. If we were building furniture =
we would never use a construction like this because we would know it was =
bound to fail.

In most cases pinblock/back separation is the result of simple glue =
failure and is not in any way related to the plate design. (I've seen a =
few exceptions but they are well beyond anything I'm going to try to =
write about here.) In modern pianos pinblock/back separation usually =
occurs because the original glue bond between the pinblock and the back =
assembly was poorly done. Or because the horizontal blockers were left =
free to expand and contract next to a multiply pinblock and they simply =
worked themselves apart as changing climate conditions caused the =
blockers to expand and contract against a relatively stable pinblock.=20

The adhesives used to assemble the modern piano back are typically =
phenol- or urea-formaldehyde assembly adhesives. These adhesives dry and =
cure to an extremely rigid glueline. They allow no glue line creep. When =
properly used they form extremely strong and stable bonds. They require =
a very thin glueline for best adhesion, however, becoming quite brittle =
and crumbly in thick section. If the glueline is even a little bit on =
the thick side, as the blockers expand and contract against the rigid =
and brittle glueline bond they simply work themselves apart.

This is also the most common cause of pinblock/back separation in the =
old upright--regardless of plate configuration--except that the glue =
joints were commonly made with somewhat more care and most of them were =
made using animal hide glue. Used correctly, animal hide glue is a very =
strong and stable adhesive. But, just as with modern adhesives, it was =
not always used correctly either. If the glue is old--having been cooked =
too long--or is at the wrong temperature--usually too cool--when joint =
closure is made the strength of the adhesive strength suffers. As with =
phenol and urea adhesives, animal hide glue is a poor gap filler; if the =
joint is wide hide glue will become quite brittle and crumbly. Hide glue =
also dries to an extremely rigid glueline having no sympathy whatsoever =
with the wood blockers need to expand and contract.

So. Regardless of plate construction, the structural integrity of the =
pinblock and back assembly depends almost entirely on the design and =
assembly quality of the back assembly--including the pinblock-to-back =
assembly fit--and on the integrity of the glue joints holding them =
together.

If you have reservations about one of these old pianos you can always =
add a few lag bolts running through the pinblock into the backpost. =
Don't bother running them into the blockers--they won't do much good =
there.


  Pitch was 100 cents low, almost uniformly from top to bottom (bass =
less, high treble more).  Can I conclude from this that the piano had =
been maintained at below 440?  Can a partial plate upright be safely =
tuned to 440 or should it be kept at, say, 435? =20
Assuming the rest of the piano is structurally sound, yes. It surely was =
to begin with.


  Pins appear to be original, or at least original size, #2 tip fits =
nicely, so re-pinning with oversize pins looks like a possibility.  =
Again, does the exposed pinblock create any special concerns with this =
approach?  Plate and case in good condition, no sign of cracks or =
separation in pinblock, but most pins don't have much more than the =
minimum amount of torque needed to stay at current pitch. =20
No. The exposed pinblock should not create any special concerns with =
repining with oversize pins. Or with rebuilding properly and replacing =
and/or plugging the pinblock. You'll find that they tune very nicely =
with the string coming off the pin so close to the pinblock surface.


  And, it was 80F and 66%RH today.
Sorry to hear about you're heat wave! Though it was pretty warm here =
yesterday as well--I think it got up to 72=BA. We all thought about =
sweltering but it really has to get above 75=BA for that to be =
convincing!

-- Del

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