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

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.

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

J.Kahn wrote:

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

Yes it crumbles, but the ice expands inside the tube giving gripping
power, so the uncrumbled ice on either side of the bend holds the
crushed ice in place. Good luck

On Mar 5, 6:26 pm, "J.Kahn" wrote:
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?

I'm sure it would crumble but the crumbled ice still won't compress.


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?


That is similar to filling it with ice except the ice is it's own
plug
and in the process of freezing it will expand, expanding the tube
to a larger diameter, or maybe splitting it, whereas filling with
water may result in the volume lost by kinking the pipe at the bend
being made up for by expanding the diameter somewhere else.

Are you sure that a weldment isn't a better design approach?
I.e. cut wedges from the inside radius, bend it, weld it. If it
MUST be smooth grind the welds flush.

--

FF

wrote:
On Mar 5, 6:26 pm, "J.Kahn" wrote:

Dennis Fetters wrote:

Morgans wrote:

"J.Kahn" wrote in message
et...

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?


I'm sure it would crumble but the crumbled ice still won't compress.


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?



That is similar to filling it with ice except the ice is it's own
plug
and in the process of freezing it will expand, expanding the tube
to a larger diameter, or maybe splitting it, whereas filling with
water may result in the volume lost by kinking the pipe at the bend
being made up for by expanding the diameter somewhere else.

Are you sure that a weldment isn't a better design approach?
I.e. cut wedges from the inside radius, bend it, weld it. If it
MUST be smooth grind the welds flush.

--

FF

Well, shoot. I guess I need to stop using ice as a method of bending
tubing if it won't work. I wish I would have know that 30 years ago, I
would have not waited all my time bending tubes that way to keep them
from distorting.......

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?

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.

We're only talking 30 degrees here guys. Sheesh!

Mark on either side of your 30 degrees. Heat the inside of the bend in
the area between the marks to a dull red, then each of you grab a side
and bend it into the hot area as if you were back peddling a canoe.
Don't add a lot of pressure. You're just "assisting" the torch heat.
Let it cool completely, and do it again if you don't have enough bend.

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

"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