Results are In! Re: moisture in wool or wood.

[Farrell]

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Yesterday, January 9 made one week that my three flanges were exposed to =
100% humidity. I inserted the same 1/8" polished drill rod into each. =
All were a little tighter than after two days. It was very difficult to =
insert the rod into all three flanges. It appears clear to me that the =
center pin hole in piano action flanges get smaller (decrease in =
diameter) as the reletive humidity (RH) increases. I will let them dry =
at 50% RH for a week and see whether they are the same tightness as when =
I first drilled them. I will then dry them in a low-RH environment for a =
week and see what happens. I'll post in a week or so.

Any comments?

Terry Farrell
Piano Tuning & Service
Tampa, Florida
mfarrel2@tampabay.rr.com
  ----- Original Message -----=20
  From: Farrell=20
  To: pianotech@ptg.org=20
  Sent: Friday, January 05, 2001 10:31 PM
  Subject: Results are In! Re: moisture in wool or wood.


  Tuesday, January 2, I started my hole in wood experiment to see if a =
hole will get smaller in diameter or larger with increased humidity. =
Rather than drilling holes in wood that may or may not reflect what =
happens with an actual flange, I took three old flanges lying around my =
shop. One was an grand damper flange, one an upright hammer butt flange, =
and one was a grand hammer shank flange. All were likely in the 40 to 80 =
year old range, and all had been sitting in my shop in 40% to 50% =
reletive humidity (RH) for months. I drilled out the flange bushings =
with a 1/8" drill in my drill press, being sure to keep things square. I =
cut three pieces of 1/8" drill rod for center pins. I filed the ends and =
polished the rod/pins so that they were nice and smooth. All three =
rods/pins fit into the flanges real easy by hand, but had no slop. My =
pinky could easily push them in and out with little effort.

  Since Tuesday the flanges have been sitting on a little plasitc =
platform in a tupperware box with a little water in the base. The =
flanges have not touched the water, but rather have been exposed to 100% =
humidity for three days. The center pin for the damper flange fits =
noticeably tighter, but was no trouble pulling it out with fingers. The =
butt flange was tighter yet. And the grand hammer shank flange was very =
tight, I could just barely push it in and get it back out - VERY tight.

  It would appear to me that the hole in a wooden flange decreases in =
diameter with increasing humidity. Am I wrong?=20

  I'm gonna wait a whole week and then check them again. After that I =
will dry them out real good and slow and check them under very dry =
conditions.

  Terry Farrell
  Piano Tuning & Service
  Tampa, Florida
  mfarrel2@tampabay.rr.com
    ----- Original Message -----=20
    From: Donald Mannino=20
    To: pianotech@ptg.org=20
    Sent: Monday, January 01, 2001 10:56 PM
    Subject: Re: moisture in wool or wood.


    Terry Farrell wrote:

      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.

    Because the whole piece of wood swells, and the hole becomes larger =
along with the piece of wood.  As I wrote in my last post, imagine the =
plug of wood which used to be in the hole.  The hole behaves the same as =
the plug of wood that was taken out.

    Do the hole and rod test.   Just pick a small piece of maple or =
something, soak it in water for a while,  then drill a hole in it with a =
spare drill.  After drilling, put the drill back in the hole, then dry =
the wood in the oven!  That drill will be really nasty tight in the =
hole!  You'll have to soak the wood again to get it out.

    There are some exceptions to this behavior:
    1. In some situations the surface fiber swelling in the hole exceeds =
the change in shape of the wood.  Key balance holes are examples of =
this, where high humidity sometimes tightens the fit.  The wood =
thickness is small, and the wood fibers are large and sometimes made of =
more reactive wood.
    2. Cross-laminated wood is more dimensionally stable, and the =
surface fibers will again have more affect on the hole size than the =
dimensional changes of the wood.  This is what happens in pinblocks.
    3. If the hole was made by compression of the fibers instead of by =
drilling and removing wood (like with a nail) then the grip on the nail =
is tighter during humid times.  All surface fiber effect, no hole to =
swell.

    Don Mannino RPT



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