jloomis wrote:
One can usually test the span, and or get a sense if there is any
bending......
It sounds like with square tubing, and 6' you have little flex.

Not from a strength of materials perspective, but from a practical
experience perspective... I'd agree with John. I can't see 2" square tube
going anywhere in a 6' span. More importantly, you are not carrying any
weight at all on that tubing, and you are not subjecting it to any forces at
all, so I just can't see it creating any problems for you. For what you are
doing, you might be able to get away with half that strength - but I'm not
advocating that. It's just a thought.

Many engineered beams take advantage of light weight plywood for the
strength
similar to "I" beam trusses....
If a person were to use that in combination with the tubing, no
flexing would happen.

I'd have to believe that a 2" I-beam would offer all the support necessary
all by itself. Think of weights like those found on barn doors which can
use either an I-beam of similar size or and open box channel, or even a
C-channel which has to be the weakest of the options. They are carrying
many, many, many more times the weight - even allowing for the fact that
they carry it over two rollers, and they last out in the elements for
decades. I'd still find the 2" box to be way more than adequate though.
Maybe even a proper level of overkill.


--

-Mike-