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?


Thanks guys.

Piano wire will be fine, and you can cold bend it as long as you don't
try for too sharp a radius and avoid nicking or dinging the wire. I'd
avoid hammering, if possible. Stress relieving the bends will improve
the life of the spring. See the "Finishing" section of this document:

http://educypedia.karadimov.info/library/springs.pdf

Keep in mind that the stiffness of your spring will vary with the 4th
power of the diameter. The 5/32 wire will be 1/2 the stiffness of the
original, and the 3/16 25% stiffer.

--
Ned Simmons