Page 256 - Making things move_ DIY mechanisms for inventors, hobbyists, and artists

234 Making Things Move

FIGURE 7-45 Extension springs (credit: McMaster-Carr)

surface, these springs are often hung from something, as in fish scales and grocery
store scales. You’ll also see them in garage door mechanisms and around the edges of
trampolines.

Torsion Springs

Torsion springs exert a torque or rotary force that’s usually used to keep something
shut. You’ve probably seen them in hair clips, mousetraps, clothespins, and clipboards.
They also live inside doorknobs, allowing them to return to their original resting
position after you open the door.

Torsion springs are a bit trickier to understand and buy, and there are a few different
kinds. Torsion springs are categorized by the angle the legs stick out from the center
spiral and the range of motion you can expect from those legs (see Figure 7-46).

Spring listings will usually give you torque only as a means of determining the strength
of the spring. This is the torque at maximum deflection (closed). However, this torque