Subject: [baidarka] bending tubes
From: hmaroske (hmaroske@freenet.de)
Date: Fri May 23 2003 - 15:58:26 EDT
Charles Hall wrote:
> Which reminds me of another question. Hendrik, how do you get those long
> sweeping bends in the tubing? Doesn't it tend to collapse? I've seen
> tubing benders for short radius bends, but not the longer gentler bends.
Tom Yost wrote:
> I may be out of line here, but I assume you're referring to the bends of the
> stringers of the kayak and ama's ? If so, there is no permanent bending,
> just the flexible aluminum tubing assuming the curvature of the cross
> sections. When removed, the tubing returns to it's original straight shape.
I'm adding:
Yes, true, that is how the long sweeping bends are obtained.
The only difference are round hatch coamings and the upswept
bow of a baidarka; here you need a tube bender. Not to mention
other sharp bends like on frames or such.
With my ultralight glider (BUG) I had to give all the wing ribs a
permanent bend; for this I used a wooden bending jig and basically
wrestled the tubes around the rig. It was difficult to eliminate the
"spring" that makes the tubes return out of shape, and once
I knew how to make a rib fit nicely, I did the whole bunch to make
sure they get the same shape. This works only for small 0.35 inch tubes.
Bending the 0.35in tubes for stabilizer and rudder was done directly
on the table over a 1:1 scale pencil drawing. Also I have a
board on a workshop wall where I can clamp a part on and visually
check if it looks OK during bending. This board is as large as
the horizontal stab.
Here is how the professionals do a bending job: at eye height!
http://rtpnet.org/robroy/baidarka/slideshow/node-x15.html
There are lots of similar construction techniques on the
Dyson aluminum baidarkas and the BUG. Bending the one-inch
upswept bottom stringer on the cockpit nose of the BUG was
a deja vu experience, it almost looks like the front piece
of a Baidarka keel.
I should get the time and make a photo collage to compare
these details...
Anyway, I admit I have a large drum full of good white
tube bending sand and never needed it. Bending aluminum
tubes can be done without sand, as soon as you get the feel
for it. If you're unsure, fill the tube with sand before
bending.
Cheers
Hendrik
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