Bending longeron

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

"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?

Good luck, without a die bender.

I have heard of some people bending tube by packing it, very tight, with
sand. I have never done it, personally.
--
Jim in NC

John ..........

It has been close to fifty years since I spent my days in the pipe shop at
Todd's Seattle, but memory serves well on this subject. It will be next to
impossible to make those bends without a bender having and internal stretch
die, or "bullet". Tubing with that thin of a wall and making that radius
guarantees wrinkles. Packing it with sand will help, of course.

There are low-temperature alloys with which you can fill the tube and then
bend it cold. You heat the alloy, pour it in the tube, and then melt it out
later. This is a clumsy operation and you may still wrinkle the tube. I
would take it to a pro with the right machine.

If you pack it with sand, put a wooden cork in one end of a long tube - the
longer the better. Stand it vertical, fill with fine, dry sand and then
spend an hour or so beating on the tube with a wooden hammer to pack the
sand. Start at the bottom and work your way to the top, refilling as
necessary. When you reach the top, smash in another plug, further
compressing the sand. We had a 20' hole in the floor of the shop with a
hoist overhead. There were three "rivet" hammers mounted to tap the pipe. We
would very slowly lower the pipe past the rivet hammers. After an afternoon
of constant rivet hammers, take a handful of aspirin.

If you end up with wrinkles, they may be artfully removed with a torch and
hammer, but it is difficult to do and requires much practice.

Regards,
Rich S.

"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

Morgans wrote:
"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?



Fill the tube with water and freeze it. Bend it with the ice inside,
this will help keep it from collapsing. It's better than trying to use
sand and cheaper than low temperature metals.

"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

Dennis Fetters wrote:
Morgans wrote:
"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?



Fill the tube with water and freeze it. Bend it with the ice inside,
this will help keep it from collapsing. It's better than trying to use
sand and cheaper than low temperature metals.


I'll experiment with that. Thanks. Doesn't the ice tend to crumble at
the bend and loose its ability to support the tube?

What about welding caps on the ends of the raw tube, one cap with a
treaded hole to take a plug, then filling with water that's had all the
air bubbles removed and plugging?

John

"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