Page 39 - Making things move_ DIY mechanisms for inventors, hobbyists, and artists

20 Making Things Move

a great way to convert from rotary to FIGURE 1-20 Rack-and-pinion gears
linear motion. Movement is usually
reciprocating, or back and forth,
because the rack will end at some
point, and the pinion can’t push it in
one direction forever.

Another common example of a
rack-and-pinion gear is a wine
bottle opener—the kind shown in
Figure 1-21. The rack in this case is
circular, wrapped around the shaft that
holds the corkscrew. The handles are FIGURE 1-21 This corkscrew uses a type of
a pair of first class levers that end in rack-and-pinion gear and levers.
pinion gears, and they go through a lot
of travel when you push them down to
give you the mechanical advantage
needed to lift the cork out of the bottle
easily.

Bevel Gears Bevel gears mesh at
an angle to change the direction of
rotation. A miter gear is a specific kind
of bevel gear that is cut at 45° so that
the two shafts end up at a 90° angle,
as shown in Figure 1-22.

Worm Gears Worm gears actually
look more like a screw than a gear, as
shown in Figure 1-23. They are designed
to mesh with the teeth of a spur gear.

One important feature of the worm gear
is the mechanical advantage it gives.
When a worm gear (sometimes just
called the worm) rotates one full