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

[Farrell]

This is a multi-part message in MIME format.

---------------------- multipart/alternative attachment
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



---------------------- multipart/alternative attachment
An HTML attachment was scrubbed...
URL: https://www.moypiano.com/ptg/pianotech.php/attachments/53/d6/b8/f9/attachment.htm

---------------------- multipart/alternative attachment--