moisture in wool or wood.

[Farrell]

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Your position is consistent with many others. It is likely I who is =
hard/thick headed. I just may go out to the shop tomorrow morning and =
drill me a hole in some maple and see what happens. Just does not make =
sense to me.  :-)  I'll report back!

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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