myths

[Leslie Bartlett]

Why do they get bigger with humidity increase in solod wood?
lesw 

-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Ron Nossaman
Sent: Saturday, December 23, 2006 10:16 AM
To: Pianotech List
Subject: Re: myths

Dean May wrote:
> Anecdotally, my experience is that marginal tuning pins are at their 
> worst in mid winter. I am aware of someone on this list experimentally 
> proving that holes shrink in dry wood. These two things seem
contradictory.
> 
> Perhaps the moisture content does more for gripping the pins than does 
> the actual interference fit.
> 
> Dean

In solid wood, the holes get bigger with humidity increase, and smaller with
humidity decrease. Pinblocks are the reverse. 
The reason is the cross ply lamination.

Dry:
(  )
I  I
(  )
I  I

Damp:
)  (
I  I
)  (
I  I

Friction coefficients do change with moisture, so that may well be a factor,
but the primary mechanism is the restriction from the cross plies.
Ron N

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