Beam Analyses

[Don A. Gilmore]

Any idiot could have made this.  All it is is a simple "plug and chug"
program.  It's not really saving you any time.  You can look up the formula
and plug the values into a calculator almost as easily.  As Ron noted, you
still have to calculate the area moment of inertia anyway.

I never trust these magical programs.  It's a good way to really screw
things up.  You put your numbers in and a magical number pops up.  Is it
correct?  Who knows?  If you don't show your work, you're really asking for
a disaster...and a disaster that you'll never be able to solve since you
have no idea how you got your answer.

I remember a salesman coming to me years ago to sell me a servomotor for a
machine application.  Servomotors are notoriously difficult to specify since
they have to be inertially matched to the load and tuned, etc.  This
salesman had a "wonderful" program that was supposed to choose a motor for
you.  He brought it up on his laptop for me.  We entered the mass of the
carriage, the pitch of the leadscrew, the friction of the bearings,
acceleration time and about a thousand other parameters.  Then the program
said, "No motor found".  So he tweaked the numbers a little: slower
acceleration, different friction, etc.  The program still said, "No motor
found".  He kept shaving the numbers and fiddling around until the program
finally said, "Motor No. 385-677".  "There you go!" he said.

I told him that if he thought that I was really going to trust a selection
like that, he must not have a very high opinion of my mental faculties.  I
eventually did the calculations myself, by hand, and came up with a
completely different motor...which I bought from another company.

Don A. Gilmore
Mechanical Engineer
Kansas City

----- Original Message ----- 
From: "Ron Nossaman" <RNossaman@cox.net>
To: "Pianotech" <pianotech@ptg.org>
Sent: Saturday, February 07, 2004 9:42 AM
Subject: Re: Beam Analyses


>
> >Utility? Comments?
> >
> >Terry Farrell
>
> For us? Not awfully handy, I think, since we would have to go elsewhere to
> figure the MOI for input, unless that's there somewhere too and I didn't
> see it. As long as we're using nominally rectangular cross section ribs
and
> figuring a center load, I think it's easier to just do this:
>
> With E being the Modulus of Elasticity in psi, which for Sitka Spruce is
> about 1570000, and load in pounds.
> In inches, Deflection= (length^3 * load)/(4*E*width*height^3)
> In millimeters, Deflection=(length^3*load)/(0.0062*E*width*height^3)
>
> Some of these on line calculators will have the formulas for the
> calculations in the page source code, in the same form as the input boxes,
> making it easy to see what they did mathematically to produce their
> answers, and cross check their methods against those from other sources
> when you get two (or more) different answers from different calculators.
> This one, like many others I've looked at, submits the information to
> another form I can't look at to do the calculations. Is there a way to go
> this? Are there any HTML gurus out there?
>
> Ron N
>
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