Humidity affects wood hole sizes

[Joe & Penny Goss]

Hin Jim,
Nice to see you posting again,
The voicing tray that I sent you was designed mostly becuase of my lack of
strength from a bout with Gillian Barre' several years ago.
I use it with a strip of emery cloth attached to wood paddles to shoe shine
file the hammers into shape.
Joe Goss
Mother Goose Music
http://www.primenet.com/~imatunr/

----- Original Message ----- From: Jim Coleman, Sr. <pianotoo@imap2.asu.edu>
To: <pianotech@ptg.org>
Sent: Thursday, August 31, 2000 10:02 AM
Subject: Humidity affects wood hole sizes


> Hi to all:
>
> I was reading in the last digest about drying tongues and flanges before
> pinning.
>
> Here's the scoop, plain and simple.
>
> Humidity causes wood to swell, Drying causes wood to shrink. In the case
> of tongues and flanges, the holes in the wood shrink when dried. This
makes
> the teflon bushing setup tighter, Humidity makes them looser. But when
> applied to felt bushings, both the wood and the felt go the same way, so
> that there is a minimum interruption from the norm.
>
> Now, every technician knows that when humidity is applied to pinblocks,
> the tuning pins get tighter. This at first glance seems counter to what
> was just said above. But here's how it works.
>
> Above, we were dealing with one hole in an unrestricted piece of wood.
> In other words the entire piece of wood was free to widen.
> In pinblocks we are dealing with multiple holes in a restricted piece of
> wood. In other words, the pinblock is fitted to the plate flange and is
> screwed to the plate with many screws. Any added humidity will cause the
> wood between the holes to expand, therefore causing a tightening of the
pin.
> I have done experiments where a 1" hole was carefully drilled through a
> 1/2" piece of hard maple. After heating and drying, the hole became
smaller,
> in the cross-grain direction mainly (W=1.437", L=1.498).
> When the wood was subjected to humidity (70% rel; W=1.505, L=1.502), the
> hole was enlarged crossgrain mostly. The original hole was drilled
> probably at around 60% rel hum in Apr.'67, so there was less variation
> seen in the humidity test above, Since pinblock material is laminated,
> you can see how that the crossgrain is held more captive than is a plain
> piece of wood such as a tongue or flange. Any swelling of the side grain
> applies pressure to the tuning pin between the longitudinal grains.
>
> In summation, it would not be a good idea to heat or dry a tongue or
> flange before pinning since the hole would enlarge with humidity and
> hence the hole would be larger and the pin looser. The pin in the
> birdseye must be tight at all times.
>
> Jim Coleman, Sr.
>