wood - was: removing key pins

[Farrell]

Thank you very much. Impressive. Your experiment may not make the cut in a peer-reviewed journal, but it goes a long way past hand waving and......"it just does." Great stuff.

Terry Farrell
  
----- Original Message ----- 
From: "Ken Jankura" <kenrpt@earthlink.net>
To: <pianotech@ptg.org>
Sent: Saturday, September 07, 2002 6:34 PM
Subject: wood - was: removing key pins


> > "Holes in wood get smaller as humidity goes down..."
> >
> > I have heard this before. Believe me, I am not trying to start an
> arguement - just trying to understand. If a hole gets smaller, then why do
> tuning pins get more loose with lower humidity?
> >
> > Terry Farrell
> >
> 
> Terry and list,
>    I did an experiment for our chapter about five years ago because I wanted
> to clear up this pesky question once and for all :-)   In addition to Bruce
> Hoadley's unequivocal assertion backed up by his experimentation that a hole
> in wood acts like the wood itself, it's nice to see it with ones very own
> eyes.
>     I used a dozen or so pieces of pine 1" x 4" x 6" separated into groups
> by moisture content; dry (as in oven), room (50%RH), and wet (underwater),
> then I drilled 1" holes through with a brad point bit, and then subjected
> them to different RH. I did leave the boards in their original and changed
> environments long enough to obtain equilibrium moisture content.
>     1) The holes in all boards became elliptical after the humidity change,
> easily measurable by calipers.
>     2) The area of the holes increased when going from dry to humid (as
> proven by the fact that with the oven dry board, after being drilled and
> placed under water, one could pass the drill bit through without touching
> the sides of the hole (if you were really careful).
>     3) The area of the holes decreased when going from humid to dry. The wet
> board, after drying, would not even accept a 15/16" drillbit.
>     Grain orientation has a lot to do with it. The closer the board was to
> being quarter sawn, the smaller the effect humidity had. Though still always
> significant and measurable.
>      I had used a smaller bit and drilled some end grain holes in the same
> boards. These holes were very stable through humidity change (I could still
> fit the drill bit into the wet board dried down, etc.)
>     Maybe not the most labratory-ish of experiments, but it proved to me
> beyond any doubt that holes in wood react as the wood would react.
> I've always thought this is why flanges work as well as they do through the
> seasons; the hole in the flange gets bigger in times of high humidity
> (remeber that S&S teflon action centers click like crazy in the summer for
> this reason), but the bushing cloth also takes on moisture and becomes
> thicker,  and in dry times the hole in the flange shrinks, but so does the
> bushing cloth, maintaining some semblance of even friction throughout the
> year. The quality of the bushing cloth will make a difference here.
>      I see keys that get tight on keypins in the winter. The hole has
> shrunk, and the bushing cloth has not shrunk as much.
>     I see tight keys in the summer, the hole has gotten bigger, but the
> cloth has grown too big with moisture.
>     Or, I see keys in the summer that are tight. It very often is with the
> first major humidity increase, and if left alone, as the keys reach
> equilibrium moisture content they are ok again. Remember that the surface
> wood will pick up moisture first, making the hole smaller but only
> temporarily until the rest of the wood catches up.
>     Still I think there were a couple guys in the chapter who were thinking
> 'I don't care what I just saw with my very own eyes, pinblocks loosen up in
> the winter, he must be wrong'. Let's please leave plywood out of discussions
> about how wood acts, it has its very own rules and differences and
> tendencies. So don't expect Delignit to act like a piece of pine or maple
> please.
> 
> Ken Jankura rpt
> Fayetteville PA
> 
> 
> 
> 
> 
>