Spring design formulae

Can anyone give me the formulae for a spiral spring? (that's the sort
that looks like an open clock spring made from a number of turns of
flat strip).

Or better still, steer me to some affordable software that would do it.
I have looked at 'Advanced spring design' from UTS but I can't afford
it! It's also worse than that, it's on annual subscription so having
paid a lot for it, you then have to do that every year!!

Thanks for any help.

 

What's wrong with the spiral function in SW?

 

Hi Matt,

Apologies - Maybe I didn't make it clear that I'm interested in
designing the properties of the spring i.e. forces etc.

Once I know how thick it needs to be, how many turns, what material
etc, I can model it!

 

I can send you the formula for torque delivered by a torsion spring.

 

The Spring Manufacturers Institute has the "Encyclopedia of Spring Design"
available for $48. You can get just the section covering spiral springs in
"Other Types of Springs" for $12.50.
http://www.smihq.org/public/pstorep.html

If you've got a favorite spring manufacturer he may give or sell you a copy.

Associated Spring used to have their own "Spring Handbook" that was very
similar to the SMI book, but I couldn't find it on their website.

The basic equations are:
M=pi*E*b*t^3*theta/(6*L)
S=6*M/(b*t^2)
ODf=2*L/(pi*((sqrt(A^2+1.27*L*t)-A)/(2*t)-theta))-A
where
M=Moment or Torque, in.-lbs.
E=Modulus of elasticity, psi
b=material width, in.
t=material thickness, in
theta=angular deflection in revolutions
L=Length of active material, in.
S=Bending Stress, psi
ODf=Outside Diameter in the free condition
A=Arbor Diameter

The last equation is only approximate.

Jerry Steiger
Tripod Data Systems
"take the garbage out, dear"