Heat tubing to a red color. Then squish in form blocks
using a bench vise. Reheat as needed.
Squishing the Ends
CHRIS TRACY, EAA 1018434
WHILE BUILDING A TUBE and fabric airplane, you will encounter
quite a few parts that require making round steel tubing with
squished ends (“squished” is an advanced engineering term).
There are two types of squished ends. One is symmetrical,
where both sides of the tube are flattened an equal amount.
The other is asymmetrical, where only one side of the tubing
is flattened. I’ll describe both of them here. Inexperienced
builders will find that the tubes can be flattened by simply
heating them to cherry red color and then, using a sturdy
bench vise, squish the ends together. You will find that this
makes sharp mark-off creases left by the jaws of the vise during the forming operation. Often one side of the tube will
flatten more than the other as well.
To ensure good symmetrical squishing, first construct the
two simple steel curved forming blocks as shown by the drawing. I used two 6-inch long pieces of old bed frame angle iron
(it’s cheap and available). The radius of the tapered end is not
critical in any way; just make it look about right with a curved
end. I made mine with perhaps a 2.5-inch radius. Be sure the
two forming steel jigs have the same curve to press the flat
ILLUSTRATION BY CHRIS LIVIERI
section to the center of the tube. I use duct tape to hold the jigs
in place in the vise.
During asymmetrical squishing, use only one of the curved
jigs in the vise. On the other side, use a straight piece of the
same angle iron as a backup that goes out a few inches on the
tubing to ensure the new squish will only take place on the one
side of the tube, and the new flat section is in line with the top
of the tube.
Now it’s time to heat the tubing to a cherry red color with
your torch. Don’t try to squish the tubing in one pass as it will
cool quickly. Reheat and keep squishing until it is flat. It seems
that the closer it gets to flat, the quicker it seems to lose its
heat, so don’t be afraid to reheat often. Cold working can lead
to significant cracking on the edges of the new flat section.
Trim and weld the ends as necessary, then reheat to a
cherry red color, and finish weld the ends as needed. Finally,
reheat the tubing to a cherry red color one more time, and
allow to cool in still air to normalize the tubing to prevent
cracking. When it has cooled, you can drill your holes in the
flattened section.
