HELICAL GEARS
A helical gear is similar to a spur gear except that the teeth of a helical gear are cut at an angle (known as the helix angle) to the axis (or hole). Helical gears are made in both right and left hand configurations. Opposite hand helical gears run on parallel shafts. Gears of the same hand operate with shafts at 90-degrees. (See Figure 1.22, 1.23, 1.24, 1.25)
BEVEL GEARS
A bevel gear is shaped like a section of a cone and usually operates on shafts at 90-degrees. The teeth of a bevel gear may be straight or spiral. If they are spiral, the pinion and gear must be of opposite hand in order for them to run together. Bevel gears, in contrast to miter gears (see below), provide a ratio (reduce speed) so the pinion always has fewer teeth. (See Figure 1.26, 1.27)
MITER GEARS
Miter gears are identical to bevel gears except that in a miter gear set, both gears always have the same number of teeth. Their ratio, therefore, is always 1 to 1. As a result, miter gears are not used when an application calls for a change of speed. (See Figure 1.28, 1.29)
WORMS & WORM GEARS
WORM Worms are a type of gear with one or more cylindrical threads or “starts” (that resemble screw threads) and a face that is usually wider than its diameter. A worm gear has a center hole (bore) for mounting the worm on a shaft. (See Figure 1.30A)
WORM GEARS – like worms – also are usually cylindrical and have a center hole for mounting on a shaft. The diameter of a worm gear, however, is usually much greater than the width of its face. Worm gears differ from spur gears in that their teeth are somewhat different in shape, and they are always formed on an angle to the axis to enable them to mate with worms. (See Figure 1.30B)
