Bending longeron

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.

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FF