Page 257 - Making things move_ DIY mechanisms for inventors, hobbyists, and artists

Chapter 7 Bearings, Couplers, Gears, Screws, and Springs 235

FIGURE 7-46 Shapes of torsion springs (credit: McMaster-Carr)

changes as you go from fully closed to fully open. Here is the equation that relates
torque to how far apart the legs are:

Torque (T) = Stiffness (k) × Angle (in radians)

NOTE Remember that degrees × ( /180) = radians.

To find the torque at an intermediate location, first figure out the stiffness (k) by using
the equation and maximum angle deflection of your spring. Then you can use the
stiffness multiplied by any angle and find the torque. You can also use a direct
proportion. For example, if the listing says 1 in-lb at 90°, then it will have 0.5 in-lb of
torque at 45°. If you want to experiment with torsion springs, revisit Project 5-1 in
Chapter 5, and you’ll have a new appreciation for the simplicity of a mousetrap.

Spring-lock Washers
Spring-lock washers, sometimes called disc washers, were mentioned back in Chapter 3
when we talked about putting them in bolted joints to help keep the joints from coming
loose. This is the most common use of spring-lock washers. They act like little
compression springs with just one revolution.