CHAPTER 14
GEARS AND GEAR CUTTING
CHAPTER LEARNING OBJECTIVES
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.
If not, you may have to find the specifications or
This chapter covers the manufacture of spur gears,
blueprints for the original gear. In some cases you
helical gears, bevel gears, stub tooth gears, worms,
should consult a machinist's handbook, which
worm gears, splines, and sprockets.
prescribes various materials. Do this to be sure the
Gears have always been a highly essential element
material you are using will hold up under the stresses
in machinery used aboard ships and at naval shore
the gear will encounter.
facilities. In today's Navy, the emphasis on speed,
Gears are made from ferrous, nonferrous, and
power, and compactness in naval machinery has created
nonmetallic materials. Steel, for example, is used
special problems for the machinist cutting a gear.
whenever great strength and toughness are required.
Today's machinists must be able to turn out a noiseless,
Nonferrous metals such as bronze and brass are often
practically unbreakable gear that transmits large
amounts of power in small spaces. This requires great
used aboard naval ships for gears that must resist
saltwater corrosion.
skill and precision.
Monel and aluminum may be used for gears, where
This chapter will cover gear cutting practices on a
corrosion resistance is of primary importance. Non-
standard milling machine. If you encounter problems
metallic gearing is frequently used where quiet
when you calculate or cut gears, consult a machinist's
operation is important. Nonmetallic gears are most
handbook for more detailed information.
effective at high-speeds. However, they do not always
As with any shop equipment you must observe all
hold up against the wide fluctuations of load and the
posted safety precautions. Review your equipment
high shock loads encountered at low speeds. Gears
operators manual for safety precautions. Also read any
made of nonmetallic materials have a lower tensile
chapters of Navy Occupational Safety and Health
strength than those constructed of metallic materials,
(NAVOSH) Program Manual for Forces Afloat,
but their greater resiliency gives them approximately
OPNAV Instruction 5100.19B, that apply to the
the same power-transmitting capacity as cast iron.
equipment.
MATERIALS USED FOR GEARS
SPUR GEARS
The choice of material for a particular gear is
A gear is made by cutting a series of equally spaced,
usually based on the function of the gear. This involves
specially shaped grooves on the periphery of a wheel
factors such as the speed of operation, the type of stress,
(see fig. 14-1).
the importance of quiet operation, and the need for
To calculate the dimensions of a spur gear, you
resistance to corrosion. The easiest way to determine
what material to use for a replacement gear is to find out
must know the parts of the gear. You also must know
the formulas for finding the dimensions of the parts. To
what material was used for the gear you must replace.
cut the gear you must know what cutter to use and how
In most cases, you will have the original gear to go by.
14-1
