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Technology: Engineering Our World
Bevel gears, Figure 8-48, change the direction in which the force is
applied. This type of gear can be straight-cut like spur gears, or they may
be cut at an angle, like helical gears.
Rack-and-pinion gears, Figure 8-49, use a round spur gear (the pinion).
It meshes with a spur gear that has teeth cut in a straight line (the rack).
The rack-and-pinion transforms rotary motion into linear (straight-line)
motion and vice versa. Figure 8-50 shows two uses for rack-and-pinion
gears.
gure 8-46. Helical gears, cut at an angle,
allow several teeth to engage at one time.
gure 8-47. In a worm and worm wheel, the worm (bottom) has only
one tooth. It spirals like a screw thread.
A B
gure 8-48. A—Bevel gears change the direction of the applied force. B—A hand drill uses
bevel gears.