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The diameter of the shaft was reduced by approximately
7% which would reduce the frequency since the moment of inertia is dependent on
the square of the materials distance from the center of the shaft. The paint is
probably an epoxy. However reducing the mass alone would increase the
frequency.
llhack
----- Original Message -----
Sent: Saturday, February 08, 2003 6:39
AM
Subject: Re: ShopTalk: A Stupid/confusing
Experiment
Hi John,
There are no stupid experiments. They all
have some merit (I'm an experimentalist). I think you are right, the
paint has a very low modulus, most plastics are three orders of magnitude down
from graphite, but the paint is at the very outside of the beam and that low
modulus material may add more than you think to the stiffness of the
shaft. My guess, though, is that the slight reduction in frequency was
mostly a consequence of the reduction in mass of the shaft. It is not
just the tip weight that controls frequency, but also the distributed weight
of the shaft. And it sounds like there was a lot of paint near the
tip. Regards.
Alan Brooks
At 08:09 AM 2/8/03
-0600, you wrote:
Hi
Folks,
You can tell it's really cold in
Wisconsin and I've got too much time on my hands.
I've always wondered why some graphite shaft manufacturers paint
their shafts to look like lolly pops. It always seemd to me that the
advantage of graphite was it's very high stiffness relative to its weight
(Young's modulus). I assumed the Young's modulus of paint has got to be
pretty damn low. I took a perfectly good orange painted Micro 58 that was
being given away at the PCS and decided to sacrfice it in the name of
science.
I took a whole bunch of
measurements on the this very fine shaft and then removed all its paint! I
tried MEK, toulene, lacquer thinner, varnish remover and some paint remover
that smelled like oranges. Nothing touch it! I finally had to scrape all the
paint off. (I was very careful not to damage the ghaphite when I removed the
point. ) Apache really knows how to paint a shaft. With the removal of the
paint the weight of the shaft of course went down. This should have
increased the frequency of the shaft. The damping effect of the paint should
also have resulted in an increase in cpms with the paint removed. Here's
what I got:
The shaft initially weighed
64.9 grams. The paint was 0.015" thick (diameter) at the tip. The frequency
was carefully measured. Before removal it ranged from 254.8 to 258.0cpm in
the weak and strong planes of the shaft. After I removed the paint the
weight dropped to 60.6 grams. The paint had added about 7% to the weight of
the shaft. Now for the weird stuff. The frequencies of the nude shaft were
now 253.7 and 256.2! The frequency went down. I guess the paint did add some
stiffness. I would not have guessd it.
Has
anyone tried making shaft out of paint? To hell with all the fancy epoxy
wraps.
Anyone interested in a rather odd
looking Micro 58?
Cheers,
John K
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