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Re: [Phys-l] Warped 2-metersticks....



"Plywood takes advantage of this by bonding many crossed layers. This
produces a product which is dimensionally stable in both directions.
However, numerous small cracks can happen in the surface."

Unfortunately this is only partially true. I built a two stop (8' and
4') harpsichord (Zukerman kit) and used it in England for three years. After about six months I noticed the sound board was pulling away from
the frame on one side where my glue job was poorest. I lifted it up and
injected glue w/ a hypo. and temporarily clamped it w/ nails. No
further change 'till I took it to Sweden to sell for my
flight back. [Wish to hell I'd returned by boat.] The buyer after only a week or two rejected it, because the sound board had expanded with a huge bulge. The west coast
of Sweden is very humid, and I now realize that my campus apartment
during English winter was dry compared to California. The sound board supplied by Zukerman
($75!) was three ply plywood, and the instructions included soaking it in a steamy shower stall.

"I wonder if the wooden meter sticks were accurately made in the first place.
Since shrinkage occurs as the wood dries, one must start with properly dried
wood before making the stick. But still most of the shrinkage should not
have a large effect on the length."

And are they pressure treated w/ a resin to prevent absorption or loss or water? I made the mistake of leaving my expensive Kung recorder on my auto dash. I couldn't believe that the bore was nearly filled w/ wax! I suppose the mfg. evacuates a chamber with the recorders immersed in wax and then lets it "down to air".

bc





John Clement wrote:

It should be possible to unwarp a wooden stick and still have its length
fairly consistent. This is because the expansion occurs mainly
perpendicular to the gain and they are very stable in the direction of the
grain. Wooden meter sticks have the grain parallel to the length. Good
cabinet makers know that you can not rigidly join extensive lengths of wood
with the grains crossed. You have to allow for expansion perpendicular to
the grain.

Plywood takes advantage of this by bonding many crossed layers. This
produces a product which is dimensionally stable in both directions.
However, numerous small cracks can happen in the surface.

I wonder if the wooden meter sticks were accurately made in the first place.
Since shrinkage occurs as the wood dries, one must start with properly dried
wood before making the stick. But still most of the shrinkage should not
have a large effect on the length.


cut

John M. Clement
Houston, TX


It is doubtful that a warped 2-meter stick can provide
accurate readings within half a millimeter even after
it has been carefully straightened out.

A number of years ago The Physics Teacher magazine
reported a comparative evaluation of wooden meter sticks.
I recall seeing a photograph of a stack of these "meter"
sticks that varied in length by as much as 2 or 3 millimeters.

Herb Gottlieb from New York City
(Where it is almost impossible to find a meter stick that is
one meter long.





On Sun, 19 Mar 2006 08:28:05 -0600 Brian Whatcott <betwys1@sbcglobal.net>
writes:

At 07:31 PM 3/18/2006, Cherie Lehman, you wrote:

Hi everyone,

I was just wondering if any of the processes suggested for

"un-warping" the

warped 2-meter sticks would disturb the spacing between the

hashmarks on the

sticks. I'd be pretty nervous about turning it into spaghetti for

fear that I
would end up with a French curve. For that matter, would the over

all length

of the stick be changed?

Just wondering.
Cherie


This is an opportune question for a person interested in measuring
something
with an accuracy of less than one half the smallest division mark
over the
length of the rule (which would be the rational lower limit of
acceptable
accuracy in a measuring stick). It is however, the sort of
question
only likely
to be answered by someone in a physics lab or class-room.
Other wood users can be content with slightly wider acceptable
tolerances.
The cheapest one meter sticks I've seen go under $2. A suitable

experimental
prospect, possibly?




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