moisture in wool or wood.

[Farrell]

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"When a wood flange swells with high humidity the action center hole =
swells also, more so with the grain than across the grain.  Think of it =
this way: when you have a hole in a normal (non-laminated) piece of =
wood, the hole behaves like the plug of wood which was removed.  With a =
large humidity increase, action center holes in the wood get slightly =
oval if they were drilled when the wood was very dry."

I have heard/read this many times, so I suppose it is true. But, =
intuitively, it makes no sense to me. If you drill a hole in a piece of =
wood and expose it to high humidity, the wood will swell - and swell =
much more across the grain (perpendicular to the grain direction) than =
with the grain. So why doesn't the hole tend to close a bit - on the two =
sides of the whole where the tangents are parallel to the wood grain.

If I take a board, drill a half-inch diameter hole through it, push a =
half-inch diameter rod through it (snug fit), and place the board in =
water or high humidity, I should think the rod would be tight in the =
wood - maybe even crack it (meaning of course that the hole gets smaller =
with increasing humidity). And if dried in a kiln or real low humidity =
environment, wouldn't the rod just fall out? I suppose I need to get a =
board and rod, but typing is easier - unless of course you don't agree =
with me! :-)  Maybe then I'll have to do the field test.

Where is the flaw in my reasoning? (I hope this post doesn't sound =
snotty - I'm trying to understand - you see, you can't see the =
inquisitive look on my face and the absence of a know-it-all look!)

Terry Farrell
Piano Tuning & Service
Tampa, Florida
mfarrel2@tampabay.rr.com
  ----- Original Message -----=20
  From: Donald Mannino=20
  To: pianotech@ptg.org=20
  Sent: Sunday, December 31, 2000 11:35 AM
  Subject: Re: moisture in wool or wood.


  Hi Gang!

  I guess I should chime in on this topic, as I've played around with =
action centers quite a bit.

  The wool cloth swells a lot with moisture changes.  This is the main =
reason action centers are so hard to manufacture so that they work in =
all climates.  You will find that the most reliable action companies =
make the centers seem rather loose if you are in a dry climate.  They do =
it that way so that it will still work in humid climates.  To really be =
reliable in Florida and Southern Texas, they need to be on the edge of =
too loose in Alberta!

  When a wood flange swells with high humidity the action center hole =
swells also, more so with the grain than across the grain.  Think of it =
this way: when you have a hole in a normal (non-laminated) piece of =
wood, the hole behaves like the plug of wood which was removed.  With a =
large humidity increase, action center holes in the wood get slightly =
oval if they were drilled when the wood was very dry.  Since the hole is =
so small, though, this effect is pretty slight.

  The wool fibers swell in all directions, but the cloth sheet swells in =
the direction that is easiest to move.  If you wet a piece of wool cloth =
laying out on a table, it will get a lot thicker and a little smaller in =
width and length.  Then it will generally stay there after it dries. =20

  If you submerge a hammer in water, it's reaction will depend on how =
tightly bound together the fibers are.  Soft hammers will bloom out into =
a fuzzy ball, while very hard hammers will hardly change shape at all.  =
I once soaked a really nasty hard sample hammer in a glass of water for =
a week, and after it dried out it sounded pretty good!

  If you wet wool cloth and place a weight on it, it will swell up =
slightly and try to lift the weight, then it will shrink back down and =
(if the weight was heavy enough) the cloth will end up a little thinner =
than it was before.  Similarly, if you put a hammer into a hammer press =
and add steam, the hammer will get smaller and harder.  This is how =
alcohol and water works to loosen a flange bushing.  Because the bushing =
is bound up by the pin and flange, the fibers try to swell with the =
moisture (the water does the work, the alcohol is sort of a "thinner" =
and penetrating agent).  They get squeezed more tightly together and =
pack the fibers more tightly together, sometimes squeezing out the sides =
a little! Then when they dry again, the bushing is thinner and works =
more freely.

  Sizing doesn't work as well after a certain point, as the wool becomes =
packed as tightly as it practically can.  If the original cloth was kind =
of cheap, wet sizing with alcohol and water gives great results, if a =
bit inconsistent.

  In theory, action centers in wood parts _should_ react less to =
humidity changes than plastic parts do, but in reality the difference is =
so slight as to not be measurable consistently.  I have done some =
experiments comparing the changes in center pin friction with extreme =
humidity changes, and sometimes I found slight differences in the change =
between wood and plastic.  In other tests, I couldn't find any =
differences, so the tests were just inconclusive.

  If you want to do some testing yourself, be sure to rebush all flanges =
with the same cloth before you start, so that you eliminate different =
cloths and pins as variables.

  Keep in mind that humidity is only one reason that action centers get =
sluggish.  In my action center class I talk about all the different =
reasons that centers go tight, and there is a pretty good list.  Cloth =
which was not originally glued into the flange in a stable position is =
one common reason (twisted cloth), as are burrs on the pins.

  Don Mannino RPT


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