Why most torsion spring failures happen at the leg, and how to get the handedness right the first time.
See Torsion Springs
A torsion spring must be loaded in the direction that closes its coils. Load it the other way and the body opens, the diameter grows, and the spring rubs or falls off its shaft. Before ordering, work out which way the arm travels in your assembly and state right hand or left hand wind explicitly.
The free angle between the legs is the angle with no load applied. Your working angle is always smaller. Give both figures plus the leg lengths measured from the centre of the body, and state whether the legs are straight, hooked or bent out of the coil plane.
Nearly every torsion spring that breaks in service breaks where the leg leaves the body. A sharp bend there creates a stress concentration in already hardened steel. A generous transition radius, formed as part of the coiling programme rather than bent afterwards, is the single biggest factor in fatigue life.
Torsion springs are usually fitted over a shaft or pin. The body diameter shrinks as the spring is loaded, so the shaft has to be smaller than the loaded inside diameter, not the free inside diameter. Tell us the shaft size and we will allow for it.
Double torsion springs use two bodies of opposite hand joined by a centre leg, which doubles torque without doubling the length of one body. Mirrored pairs are used where two springs work on either side of a hinge. Both are standard work.
Hold it with the coils facing you. If the wire spirals away clockwise from the near leg it is right hand wound. Sending a photo from the end usually settles it faster than describing it.
Not reliably. Design for one loading direction. If your mechanism needs return in both directions, two springs or a different mechanism is the better answer.
Send the part, the load and the environment. A short email usually settles a specification faster than any guide can.
