Re: RE: Units of measurement?

From: <kbdmccrory_at_comcast.net>
Date: Sat, 11 Mar 2006 00:29:23 +0000

In response to the diversion, test and compare the calculators and discover what has been "helped".

Don, I'm sure that your local lumber yard would like to sell you No.4- utility grade cedar - for coffins, you'll need one to hold the stuff - at C-select prices. Besides appearance, there is a lot of mechanical difference. But there have been standards established for structural materials. When the numbers are changed and advertised as the genuine article, who suffers and who benefits?

I asked the question about units of measurement for those of us who are curious and enjoy more detailed aspects of this hobby. The intent and motivation in developing a "strength" program for balsa includes the opportunity to actually research the material, rather than arbitrarily crank up a multiplier.

So, take potshots at honesty.

Bruce
In Seattle



-------------- Original message --------------
From: Don Slusarczyk <don5490_at_sbcglobal.net>
Stiffness Coefficient is just that a coefficient, it is dimensionless.
All that matter is how the scale works. Bernards original could have
equated 1000 as normal instead of 100, or even 367.6 for that matter. It
is a relative factor and was really intended to compare wood of similar
range densities 4.2 to 4.5 pound, and not for 4 to 6#. Bernard had
stated that as the wood density goes up that the SC value of "good" wood
drops, 135 is good for 4 # but 100 for 7 pound was excellent as the
scale is not linear. The best way is to calculate the elastic modulus of
the wood and if you look in an old NFFS Symposium then you will find how
Jim Richmond tested his wood, and in that article is a graph of Elastic
modulus (Youngs modulus or E) vs density of wood. Jim graphed some
points on that sheet so you can use that to see how your wood compares.
It is easy to get caught up in the math. And I think people incorrectly
assume 100 means average for all densities, and that is not true using
Bernards SC formula. I do not know what Tim did to modify the formula
but it really does not even matter, all it means is you need to use the
same SC formula for all your wood. Hopefully Tims changed helped to
linearize the scale a little bit.

Don

> > -----Original Message-----
> >
> > I am working on a clean calculator for Hunt's Stiffness Coefficient.
> > The current downloadable version has been corrupted.
>
>
> Corrupted to Bruce means that I implemented a slight change to the
> calculations of the download version on my site about 2 years ago. This
> slight change makes the results for indoor sized sheets in thicknesses
> over
> .045" actually match real world results. For some reason Bruce thinks that
> it is more appropriate to perpetuate theoretical results that do not
> square
> with the real world.
>




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Received on Fri Mar 10 2006 - 17:03:38 CET