Re: steel tubing strenght formulas ?? plasma table

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "metlmunchr"
<metlmunchr@y...> wrote:

>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "turbulatordude"
> <davemucha@j...> wrote:
>
> > yikes ! A 3 inch squate tube with 1/8 wall and only a 50 pound
> > load will deflect about 4 thou.
> >
> > A 100 pound load will deflect about 8 thou.
> >
> > Neither is too bad for a plasma cutter, but both are horrible for

a

> > router.
> >
> > Dave
>
> Dave, the end conditions are a big factor in deflection. if you

have

> a leg at each end of the tube and nothing else but the single tube
> tying the legs together then the ends of the tube would be

essentially

> free and you'd get max deflection for a given load. If there's a
> second member tying the two legs together, then the end condition of
> the tube more approaches fixed end conditions which result in less
> deflection. Vertical bridging between the two horizontal members
> creates a truss which can drastically reduce the deflection since

its

> roughly related to the cube of the height. The AISC Manual for

Steel

> Construction covers situations like this, but structural analysis in
> general is not a quick and simple thing once there are redundant

load

> paths, etc.

I can see that to a large degree.

I'm looking at a plasm table and want to have a part of 5 ft by 12
ft. If I ran a pair of 3" squares say, 12 inches apart and then
every two feet just ran a secton to join them, I'd spread the load
considderably. And, if I have 4 legs on a side that would
effectivly make each section 3 feet long.

I thought about a recent discussion of looooong tables and thought
about a smaller table with extentions. It seems that making a 5 ft
x 5 ft table would be easier, and then add roller extentions on the
ends for indexing the part.

So, in design, I am looking for the costs of making a full huge table
and the expenses for that, and the costs of making a smaller table.

It seems that a modular table would be really easy so that is a
definate option.

But, with a plasma, a water tray under is often needed to catch the
spray, and under that might be storage for sheets of metal.

Dave