The larger gear is called the Gear and the smaller, the Pinion. Usually when two gears are in mesh and one is larger than the other, the names gear and pinion are applied. Spur gears are used to transmit power from one shift to another in cases where those shifts hake their axes parallel. Bevel gears are not restricted to shafts at right angles. There are right angle bevel gears and angular bevel gears. These gears permit the driving of one shaft at right angles to the other.
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Upon completing this chapter, you should be able to do the following: Describe the materials used to manufacture gears. Explain the manufacture of gears, splines, and sprockets. Explain the process used to set up gear trains. This chapter covers the manufacture of spur gears, helical gears, bevel gears, stub tooth gears, worms, worm gears, splines, and sprockets.
Gears have always been a highly essential element in machinery used aboard ships and at naval shore facilities. This requires great skill and precision. This chapter will cover gear cutting practices on a standard milling machine. As with any shop equipment you must observe all posted safety precautions. Review your equipment operators manual for safety precautions. This involves factors such as the speed of operation, the type of stress, the importance of quiet operation, and the need for resistance to corrosion.
The easiest way to determine what material to use for a replacement gear is to find out what material was used for the gear you must replace.
In most cases, you will have the original gear to go by. If not, you may have to find the specifications or blueprints for the original gear. Do this to be sure the material you are using will hold up under the stresses the gear will encounter. Gears are made from ferrous, nonferrous, and nonmetallic materials. Steel, for example, is used whenever great strength and toughness are required. Nonferrous metals such as bronze and brass are often used aboard naval ships for gears that must resist saltwater corrosion.
Monel and aluminum may be used for gears, where corrosion resistance is of primary importance. Non- metallic gearing is frequently used where quiet operation is important. Nonmetallic gears are most effective at high-speeds. However, they do not always hold up against the wide fluctuations of load and the high shock loads encountered at low speeds.
Gears made of nonmetallic materials have a lower tensile strength than those constructed of metallic materials, but their greater resiliency gives them approximately the same power-transmitting capacity as cast iron. To calculate the dimensions of a spur gear, you must know the parts of the gear. You also must know the formulas for finding the dimensions of the parts. To cut the gear you must know what cutter to use and how Figure The symbols in parentheses are standard gear nomenclature symbols used and taught at MR schools.
In parallel shaft gears, you can determine the pitch diameter directly from the center-to-center distance and the number of teeth. The following list will familiarize you with both sets of symbols: Machinery.
Gear Production with Vertical and Horizontal Hobbing Machines From EMAG
For example, if a spur gear is being produced, then the hob is angled equal to the lead angle of the hob; if a helical gear is being produced then the angle must be increased by the same amount as the helix angle of the helical gear. The hobbing features for gears are straight, helical, straight bevel, face, crowned, worm, cylkro and chamfering. If the hob has multiple threads the speed ratio must be multiplied by the number of threads on the hob. Each gear hobbing machine typically consists of a chuck and tailstock , to hold the workpiece or a spindle, a spindle on which the hob is mounted, and a drive motor. The necessary addendum correction to allow the use of small-numbered pinions can either be obtained by suitable modification of this rack to a cycloidal form at the tips, or by hobbing at other than the theoretical pitch circle diameter. Since the gear ratio between hob and blank is fixed, the resulting gear will have the correct pitch on the pitch circle, but the tooth thickness will not be equal to the space width.
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