Sizing Key Mortises (was inconsistent rail pins)

[John Ross]

How about, as the wood dries, it shrinks. Since the fibres of the wood, lie 
in a line front to back in the key, in the drying the fibres get closer 
together, so the hole gets smaller, resulting in a tightening around the 
keypin.
John M. Ross
Windsor, Nova Scotia, Canada
jrpiano at win.eastlink.ca
----- Original Message ----- 
From: "William R. Monroe" <pianotech at a440piano.net>
To: "Pianotech List" <pianotech at ptg.org>
Sent: Monday, September 11, 2006 11:46 PM
Subject: Re: Sizing Key Mortises (was inconsistent rail pins)


> OK,
>
> I'm also in a cold dry winter climate, and this year I'll do the 
> experiment with one of the materials of our trade.  I'll measure a key now 
> and over the course of the next year, and see what I find.  I have never 
> experimented to check this phenomena, but by the books, it wouldn't 
> happen.
>
> Wood fibers swell with moisture, shrink as they dry.  A quick read of a 
> book like Hoadley's "Understanding Wood" supports this idea, no matter the 
> wood. The rates vary depending on what cross section of the wood we look 
> at (tangential, radial, or longitudinal).
>
> I asked a wood scientist at the University of Wisconsin, Roger Rowell, 
> about techs suggesting the pin holes in flanges would shrink as they dry. 
> He said, categorically, no.  So, I've always wondered what complicating 
> factors might be at work here to cause some techs to get these "tighter 
> when dry" readings.  I dunno.
>
> Let's be clear, I'm not saying tighter frictions can't happen during the 
> dry season, but my feeling is it is not because, "drying wood swells."
>
> I'll be measuring..................
>
> Regards,
> William R. Monroe
>
>
>
>>>From my experience out here in Québec (cold & dry winters) the
>> keybushings will get tighter with humidity going down, not the opposite.
>> If you take measurements of the key width when humid and then when dry,
>> the dry key will be smaller than the wet one. So, the mortise will be
>> smaller as well.
>>
>> Marcel Carey, RPT
>> Sherbrooke, QC
>>> Hi Terry, List,
>
>