"Jim Wilkins" writes:

"Richard Smith" wrote in message
...
Jahan writes:

8 cm wide by 3 cm U Channel and 3 x 3 inch x 2 mm tube

....
You'll be wanting to study Second Moment of Area and the beam and
column calculations / equations.
The Euler column and the Euler-Bernoulli beam (both derived around
the
1750's - about 250 years ago) which serve well for most applications
of beams and columns.

Regards,
Rich Smith

When I built a log splitter, sawmill and a hydraulic bucket loader for
my tractor I welded every joint that wouldn't have to be taken apart
to store or modify them. However structural steel design manuals say
to avoid field welding whenever possible, due to high cost. They are
more neutral about shop welding versus bolting. Why would field
welding be prohibitably expensive? Heavy construction equipment is
almost entirely welded.

Big difference between commercial and hobby, in all practical / real
senses.

That contention, "field welding expensive", would be true for typical
commercial cases.
Commercially, you use MIG (GMAW) in a workshop, and SMAW on-site

* in a well-set-up fab-shop MIG (GMAW) is vastly faster than stick
(SMAW) applied in the same situation

* they'd be talking about bolted steel connections for buildings -
"rattle-gun" (impact wrench) a few bolts, rather than weld (SMAW)
(noting that at the ends of beams, where the bolts are, you only
have a small shear force, with all the serious big beam bending
stresses far away in the mid-length of the beam)

Hence, commercially, due to processes used and the majority
application, the statement is true.

In a hobby workshop, at best you still have a single-phase electric
power and you cannot pull those 15kW from the mains which makes
fabshop MIG so productive. Most MIG's are transformer and something
like 50% efficient, whereas many SMAW sets now are inverters and
high-90's percent efficient - so those 3.12kW (British 240V 13A max)
give almost twice the bang-per-buck and even up the productivity. No
loss of productivity outdoors with stick, which is one of the few
processes which is in reality rather tolerant of wind and rain.
Then you are going to have much more trouble making bolted joints that
in a well-set-up commercial shop, with all your marking tools,
benches, ironworker for punching holes, etc, etc, etc.

In summary - it's no wonder you see a different picture where for your
home fabs. welding is vastly easier and quicker.

It all makes complete sense - be assured of that.

Regards,
Rich Smith