Bending longeron

"Maxwell" wrote in message
...

"J.Kahn" wrote in message
.. .
I need to make bends of about 30 degrees in a 3/4 x .049 longeron tube,
with a tight bend radius, no more than 3 inches. Can I do the bend hot
without wrinkling the tube by free bending or do I need a supporting die
of some kind? Anybody have any specific techniques?

John

I think I would try slipping a tension spring inside the tube if you can
find one the right size. A 5/8" o.d. might be close enough, it would
leave about .025" depending on how close the tube and the spring are to
actual size.

Also, I think a 3/4" electrical conduit bender will give you about a 4"
radius, depending on brand. If that doesn't work, you might try making a
square shouldered bending shoe out of 3/4" plywood for a tube that thin.
Don't know for sure, just a wag. Thirty degrees isn't very far.

Max

Come to think of it, you might be able to wrap another spring around the
outside, and go 30 degrees without a benging shoe. But obviously I'm still
guessing.

*Nothing is too difficult for the man that doesn't have to actually do it.*

J.Kahn wrote:
I need to make bends of about 30 degrees in a 3/4 x .049 longeron tube,
with a tight bend radius, no more than 3 inches. Can I do the bend hot
without wrinkling the tube by free bending or do I need a supporting die
of some kind? Anybody have any specific techniques?

John

John,

They make special heavy springs which fit inside
tubes to support the inside radius of the bend and
keep it from collapsing when you bend it. Pulling
on the spring causes its outside diameter to get
slightly smaller so that you can get it out of the
bent tube after you're done.

Check at automotive parts stores and Harbor Freight.

Good luck with it,

Don W.

J.Kahn wrote:
I need to make bends of about 30 degrees in a 3/4 x .049 longeron tube,
with a tight bend radius, no more than 3 inches. Can I do the bend hot
without wrinkling the tube by free bending or do I need a supporting die
of some kind? Anybody have any specific techniques?

John
--I bent some of the same tube by filling it with sand, bending it
around a 10" pulley that had been turned out inside to 3/8"
radius--Pulling it around with the inner race of a big ball brg that had
used 3/4" balls--this was pressed onto a smaller brg which was bolted to
a bar that pivoted on the center support of the pulley. BUT--
that's a 5" radius & you want 3"---might do it though..send ya a pic if
your interested. wass biplane at tds dot net

On Mar 5, 2:29 pm, Jerry Wass wrote:
J.Kahn wrote:
I need to make bends of about 30 degrees in a 3/4 x .049 longeron tube,
with a tight bend radius, no more than 3 inches. Can I do the bend hot
without wrinkling the tube by free bending or do I need a supporting die
of some kind? Anybody have any specific techniques?

John

--I bent some of the same tube by filling it with sand, bending it
around a 10" pulley that had been turned out inside to 3/8"
radius--Pulling it around with the inner race of a big ball brg that had
used 3/4" balls--this was pressed onto a smaller brg which was bolted to
a bar that pivoted on the center support of the pulley. BUT--
that's a 5" radius & you want 3"---might do it though..send ya a pic if
your interested. wass biplane at tds dot net

Can't you use a conduit bender?
Lou

Lou wrote:
On Mar 5, 2:29 pm, Jerry Wass wrote:
J.Kahn wrote:
I need to make bends of about 30 degrees in a 3/4 x .049 longeron tube,
with a tight bend radius, no more than 3 inches. Can I do the bend hot
without wrinkling the tube by free bending or do I need a supporting die
of some kind? Anybody have any specific techniques?
John
--I bent some of the same tube by filling it with sand, bending it
around a 10" pulley that had been turned out inside to 3/8"
radius--Pulling it around with the inner race of a big ball brg that had
used 3/4" balls--this was pressed onto a smaller brg which was bolted to
a bar that pivoted on the center support of the pulley. BUT--
that's a 5" radius & you want 3"---might do it though..send ya a pic if
your interested. wass biplane at tds dot net

Can't you use a conduit bender?
Lou

Apparently you can but the radius I need is smaller than a conduit bender.

"J.Kahn" wrote

Apparently you can but the radius I need is smaller than a conduit bender.

Use that, then tweak it?
--
Jim in NC

A standard hydraulic tubing bender for 3/4 OD tubing has a 3" radius
to tube centerline and says the minimum wall without flattening is
0.049 for "high strength" aluminum, or any for soft aluminum. If you
have a piece to try, head to your local hydraulic shop and ask them to
try.

With inner support, there is lots more capability, and as close as
this is, the spring will probably be enough.

On Mon, 05 Mar 2007 11:01:37 -0500, "J.Kahn"
wrote:

I need to make bends of about 30 degrees in a 3/4 x .049 longeron tube,
with a tight bend radius, no more than 3 inches. Can I do the bend hot
without wrinkling the tube by free bending or do I need a supporting die
of some kind? Anybody have any specific techniques?

John

On Mar 5, 9:01 am, "J.Kahn" wrote:
I need to make bends of about 30 degrees in a 3/4 x .049 longeron tube,
with a tight bend radius, no more than 3 inches. Can I do the bend hot
without wrinkling the tube by free bending or do I need a supporting die
of some kind? Anybody have any specific techniques?

John

This is easy to do with a torch. Secure the tube to your table, with
the horizontal tube tacked into place forward of the bend. Set your
torch with a neutral flame and heat to cherry red for about 2.5 inches
either side of the bend. Slowly bend to the desired dimension. If
your using a wood topped jig table, place a small piece of steel
between the tube and the table. Header wrap also works well to keep
from burning the table too much. If you're bending both the top and
bottom longeron you will have to alternately heat each tube at the
same time. If you're bending one tube alone, a conduit bender works
well. Practice with cheap conduit to get the hang of it first. Also
practice your bending with the torch on small scrap 4130 until you
feel confident with the process. If you go slowly, and don't over
heat, you will have a nice radius bend with no wrinkle.

Colin

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