Pinning on new flanges

[Dave Nereson]

----- Original Message ----- 
From: "Richard Brekne" <Richard.Brekne@grieg.uib.no>
To: "Pianotech" <pianotech@ptg.org>
Sent: Tuesday, August 24, 2004 2:25 AM
Subject: Re: Pinning on new flanges


> Hi Bob
 . . . . .
> Interestingly enough, it is the position of the Yamaha factory that
> wooden flanges with felt bushings remain quite stable with regards to
> tightness as (they say) the reactions of the wood holes, and felt
> bushings are very close to exactly opposite to climatic changes.

>RicB

     I once pinned a flange in ambient room conditions to the tightness to
which I usually pin a hammer flange.  Then I left it on top of the stove,
right over the pilot light, where it would get quite warm, but, sitting on
porcelain-covered metal, would not burn.  After a couple days I tried the
tightness of the pin and it felt about the same.  Then I threw it into a jar
of water, let it soak for a day, then tried the pin again and it felt about
the same.
   With a pine shelf board, like a 1" x 8", or a section of soundboard, it's
easy to picture the grain, which way it runs, and which way it expands and
contracts with changing humidity.   Now, the shelf board is probably
flat-sawn, while the soundboard is (we hope) quarter-sawn, or somewhere in
between.  But with a flange, it's a little harder to figure out how it was
oriented in the log it came from.  In which direction does it expand and
contract the most?  What happens to the center pin hole when it gets humid?
My little un-scientific experiment suggests "not much", as does Yamaha's
position.  Are they saying that when humid, the flange gets bigger, but it
expands in all directions, thus shrinking the hole a little, counteracting
the expansion?  And vice versa?
    Should we pin flanges tighter when it's humid and looser when it's dry,
or doesn't it matter?
    --David Nereson, RPT