Re: re:RE: LARGE Gantry table

Lindsay,

FEA= Finite Element Analysis. A search will give you more information
more completely than typing here.

A quick summary is that the structure is divided into small parts
(the finite elements), and the stress on each is calculated. This
result is often then presented visually. Many times using gradations
and hues of color...

Hope this helps,

Ballendo

P.S. FFT would be Fast Fourier Transform...

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Lindsay" <xdonna@b...> wrote:
> Elliot,
> An FEA anaylsis? Is'at a fourier transform or something? I'm not an
engineer
> so I'm not sure what you mean.
> I woudn't mind building an oversize table myself but more on the
order of 6'
> x 12', I'm in the sign business and this would be a good size for
routing
> sign faces etc. When I think of a triangular space frame I envision
the
> welded tubular structures that they hang road signs on over the
freeway.
> Lindsay
> ----- Original Message -----
> From: "Elliot Burke" <elliot@h...>
> To: "CAD_CAM_EDM_DRO" <CAD_CAM_EDM_DRO@yahoogroups.com>
> Sent: Wednesday, March 10, 2004 11:34 AM
> Subject: [CAD_CAM_EDM_DRO] re:RE: LARGE Gantry table
>
>
> > Just a thought about the weight of a 20 ft gantry,
> > If you are really going to build a 20 ft gantry, shouldn't it be
built
> like
> > large structural spans usually are: as a space frame? Bridges
can usually
> > do without much torsional stiffness, so they aren't space frames,
but you
> > see lots of space frames holding up the roof in stadiums. Race
cars use
> > these a lot too.
> >
> > If welded steel tube doesn't do it for you, then graphite/epoxy
is the
> next
> > step up. Aluminum has about the same stiffness/weight as steel,
so it has
> > no advantage in this sort of structure.
> >
> > A space frame is one of the two most efficient structures, and is
great
> for
> > connecting concentrated loads over large distances. Welded steel
tubing
> > does it. All triangles -> all members are stressed in tension or
> > compression, no bending.
> >
> > Like Les said, a FEA analysis is a good idea. The tubes can be
modeled as
> > beams of appropriate moment of intertia. This simplifies the
> model/reduces
> > number of nodes considerably.
> >
> > regards-
> > Elliot
> >
> >
> > Chris, Les, and others wrote about a 20 ft gantry:
> >
> > Heh. Confused Chris? My friend Bob Campbell said a Gecko would
> > handle it. I said it would need something bigger.
> >
> > To put things in perspective my 1000 lb gantry IS run by a Copley
> > 412 which is about the same as a Gecko in power. So Bob is
absolutely
> > correct for the weight you asked about.
> >
> > I just think that a 20 ft gantry will be much more massive than my
> > system. Things tend to go up in mass as the cube of length for
equivalent
> > stiffness. Sometimes even more. A finite element structure
analysis
> > can define this in the design stage.
> >
> > Les
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