Sizing Key Mortises (was inconsistent rail pins)

[William R. Monroe]

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,