Page 37 - Making things move_ DIY mechanisms for inventors, hobbyists, and artists

18 Making Things Move

FIGURE 1-18 A turnbuckle can be used to tighten or loosen the tension in a cable.

the turnbuckle has left- and right-hand threads. Most screws that you’ve encountered
have a standard right-hand thread, which means they get tighter as you turn them
clockwise, or to the right. Left-hand threads get tighter when you turn the screw to
the left, or counterclockwise. By using one of each, the turnbuckle can either draw in
both sides at once to tighten or loosen both sides simultaneously. This same idea can
be used in leveling mechanisms as well. You can also find power screws in C-clamps
and vises.

You’ll also find power screws in positioning systems where precise location, rather
than mechanical advantage, is the main concern. These types of systems use motors
to turn a power screw that positions a table or other mechanism horizontally or
vertically. You can see these systems in 3D printers and precision lab equipment. (For
some good examples of power screws, visit www.velmex.com/motor_examples.html.)

6. Gears

Gears are used to magnify or reduce force, change the direction or axis of rotation, or
increase or decrease speed. Two or more gears in line between the input and output
are known as a drive train. Drive trains that are enclosed in housings are called
gearboxes or gearheads. The teeth of the gears are always meshing while they are
being turned, so a gear drive train is an example of a positive drive.

Gear Types
There are many different types of gears and ways to use them. We’ll cover the details
in Chapter 7. Here, we’ll take a look at the five basic types of gears: spur, rack-and-
pinion, bevel, worm, and planetary. 2