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Types of Gears (Các kiểu bánh răng)

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    is cylindrical in shape, with teeth on the outer
    circumference that are straight and parallel to the axis (hole).
    There are a number of variations of the basic spur gear,
    including pinion wire, stem pinions, rack and internal gears.
    (See Figure 1.17)

    is a long wire or rod that has been drawn
    through a die so that gear teeth are cut into its surface.
    It can be made into small gears with different face widths,
    hubs, and bores. Pinion wire is stocked in 4 ft. lengths.
    (See Figure 1.18)

    are bore-less spur gears with small numbers of
    teeth cut on the end of a ground piece of shaft. They are
    especially suited as pinions when large reductions are
    desired. (See Figure 1.19)

    are yet another type of spur gear. Unlike the basic spur
    gear, racks have their teeth cut into the surface of a straight
    bar instead of on the surface of a cylindrical blank. Rack is
    sold in two, four and six foot lengths, depending on pitch,
    which you will learn about starting in chapter 2.
    (See Figure 1.20)

    have their teeth cut parallel to their shafts
    like spur gears, but they are cut on the inside of the gear blank.
    (See Figure 1.21)

    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)

    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 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)

    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)

    Worms and worm gears work in sets, rotating on shafts at right
    angles to each other, in order to transmit motion and power
    at various speeds and speed ratios. In worm and worm gear sets,
    both the worm and worm gear are of the same hand. (Because
    right- hand gearing is considered standard, right-hand sets will
    always be furnished unless otherwise specified.) (See Figure 1.30)


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