"Tim Wescott" wrote in message
...
On Fri, 19 Jun 2015 18:15:00 +0800, Techman wrote:

I need to replace a broken light duty torsion spring and need some
advice.

It's broken right at the bend, I may be able to buy a new one but
it
will have to come from the UK to Australia and I need it ASAP.

https://dl.dropboxusercontent.com/u/...ring%20(1).JPG

https://dl.dropboxusercontent.com/u/...ring%20(2).JPG


The spring returns an aluminum flap through and rotates through an
angle
of around 90°.
The wire diameter is 4.5mm and the overall length of the spring is
around 24".


I can get some 3/16" diameter "piano wire" (4.76mm) or 5/32" (4mm)
from
my local hobby shop. Will piano wire work OK as a spring in this
sort of
application?


Will I have trouble cold bending the ends?

I was thinking of drilling a 5mm hole through a heavy piece of
metal and
using pipe, then a hammer, applying the bend. I would try to leave
a
more generous radius than the on the original.

Thoughts?

What everyone else has said, except that to bend it I'd put it in a
vice,
pointing straight up, with a couple of bits of 1/16" thick soft
aluminum
on the bend side to act as a sacrificial one-time wire bending tool.
Bending it down onto the aluminum (instead of across the sharp jaw
of the
vice) should give you a reasonable radius.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com


If I didn't have conical mandrels I'd turn a groove of the desired
inside radius in a piece of scrap from the cutoff bin, clamp it
upright in the vise with the groove just above the jaws, and use pipe
(or padded Vise-Grips) as handles to bend the rod as far as it will
stay tight in the groove. When the back side begins to pull out I'd
rotate it 45 degrees in the vise to catch the back side under the jaw,
and continue.

Take it out before it's done and check the bend radius. You may want
to turn the groove smaller by the amount of springback.

-jsw