Humidity affects wood hole sizes

[Paul S. Larudee]

Wow, Jim.  That was a spectacular response, more than I hoped for.  And you
addressed the specifics I raised even before I raised them!   Can you teach me
telepathy?

Now how about bridge pin holes and Richard's idea of drying the holes and
inserting the new pin?

It's great to have you on line.  Are you still pushing your wife around....er, I
mean wheeling her around?  How about a progress report?  Hope to see you at the
next convention.

Paul S. Larudee, RPT

"Jim Coleman, Sr." wrote:

> 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.