re:Re: re:RE: LARGE Gantry table

FEA is finite element analysis. This is a method of calculating the
strength and other mechanical properties of a design structure - before
building it. Pretty good idea for large structures.
For example, you'd want to know the resonanant frequency. If it resonated
at 5 Hz, that would be bad..... 100 Hz probably OK.
FEA is done with specialized software. Mostly its done by specialists,
although there is some software usable by non-specialists.
The specialist does only FEA analysis. Some spend their days doing FEA
analysis only of one particular type of structure, oil tankers, for example.
I'm an optical engineer who dabbles.

regards-
Elliot


Linday 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@...>
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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