Square tube has some fairly loose specs, hot rolled product is even looser.

ASTM specs for tube call for the corner radius to be no more than 3x the
wall thickness. This means that a 2" square tube with .250 wall could
have 3/4" radius on each corner with only 1/2" of flat. This would look
more like a mildly deformed piece of round pipe than a traditional
square tube. What this means is that the mfg can make most any
reasonable radius on the corners and it will meet spec. It also means
that you can not depend on the radius to be the same from lot to lot.

When they mfg square tube they take some slit flat stock, roll it up,
weld it, then run it through a 'turk's head' roller to make it square.
If the slit stock is a bit narrow, the round portion will have a smaller
diameter, the resulting square section will have more rounded corners.
Since the mfg buys his steel by the pound, they have incentive to use
less, results in rounded corners on the cheaper tube.

Hot rolled angle is even worse. The only dimension that you can
reasonably count on is the 90 degree corner, and even that varies some.
The leg length can vary considerably, a 3-3/4" leg length on 4" angle is
fairly common. The inside shape is done with a roll that will vary from
one rolling mill to the next, multiple rolling dies at the same mill may
be more or less worn so you can't even count on the shape being the
same. Some will have a very large radius in the corner, some will have
tapered sides, some will have a smooth rounded edge, others will be
almost knife sharp. Most of this product is made is US mini mills from
scrap or imported. Neither is what I would call a 'prime' producer.

The horror story: we set up a robot to weld a frame that included some
4" angle brackets. The position was fixed by a stop block on the 90
degree face, the robot welded the lip. Things started out ok, then we
had a series of weld failures on the angle bracket. It seems that the
robot expected 4" legs, the low side tolerance was around 3-3/4". The
robot was welding a bead on the base metal, never even got near the
angle. We had to put in a "sense" op in the program where the robot head
moves in to find the edge, then starts welding. Slowed it down
tremendously, gave up on that. Finally had the robot weld the back side
to position the part, did a final edge weld manually.

It's amazing what you learn when you buy full truckloads of material and
then get to do the quality control after it has already been cut to
size. Sigh.

thito01 wrote:
Can anyone point me to a table with the standard radius for corners for
different steel forms?
I want to place 2x4 tubing inside either a 3" or 4" angle iron and don't
know if the inside radius of the angle iron will allow the 2x4" tubing to
set 'flat' on both legs of the angle iron.


TT



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