Re: [CAD_CAM_EDM_DRO] re:RE: LARGE Gantry table

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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