Fundamentals of Gears

Several types of gears are in common use. Four principal

types of gears are:

• Spur gears

• Helical gears

• Bevel gears

• Worm gears.

Gear

Gears are toothed cylindrical wheels used for transmitting

mechanical power from one rotating shaft to another.

Several types of gears are in common use. Four principal

types of gears are:

• Spur gears

• Helical gears

• Bevel gears

• Worm gears.

Type of Gear

Gears are toothed cylindrical wheels used for transmitting

mechanical power from one rotating shaft to another.

Several types of gears are in common use. Four principal

types of gears are:

• Spur gears

• Helical gears

• Bevel gears

• Worm gears.

Type of Gear

Gears are toothed cylindrical wheels used for transmitting

mechanical power from one rotating shaft to another.

Several types of gears are in common use. Four principal

types of gears are:

• Spur gears

• Helical gears

• Bevel gears

• Worm gears.

Type of Gear

Gears are toothed cylindrical wheels used for transmitting

mechanical power from one rotating shaft to another.

Several types of gears are in common use. Four principal

types of gears are:

• Spur gears

• Helical gears

• Bevel gears

• Worm gears.

Type of Gear

Gears are toothed cylindrical wheels used for transmitting

mechanical power from one rotating shaft to another.

Gear Materials and Useful Ratios

Nomenclature of Spur Gear

Nomenclature of Spur Gear

Pitch circle. This is a theoretical circle on which calculations are

based. Its diameter is called the pitch diameter.

Nomenclature of Spur Gear

Circular pitch. This is the distance from a point on one tooth to the

corresponding point on the adjacent tooth measured along the pitch

circle.

Nomenclature of Spur Gear

Tooth thickness. This is the distance from a point on one face of

tooth to the corresponding point on the adjacent face of the same

tooth measured along the pitch circle.

Nomenclature of Spur Gear

Module. This is the ratio of the pitch diameter to the number of teeth.

The unit of the module should be millimeters (mm). The module is

defined by the ratio of pitch diameter and number of teeth.

Nomenclature of Spur Gear

Diametral pitch. This is the ratio of the number of teeth to the pitch

diameter. Thus, it is the reciprocal of the module. Since diametral pitch

is used only with U.S. units, it is expressed as teeth per inch.

Nomenclature of Spur Gear

Addendum, a. This is the radial distance from the pitch circle to the

outside of the tooth.

Dedendum, b. This is the radial distance from the pitch circle to the

bottom land.

Nomenclature of Spur Gear

Clearance circle. This is a circle that is tangent to the addendum

circle of the mating gear.

Clearance, c. This is the is the amount by which the dedendum in a

given gear exceeds the addendum of its mating gear.

Conjugate Action Mating gear teeth acting

against each other to

produce rotary motion

are similar to cams.

When the tooth profiles,

or cams, are designed

so as to produce a

constant angular velocity

ratio during meshing,

these are said to have

conjugate action.

Involute Profile Mating gear teeth acting against each

other to produce rotary motion are

similar to cams. When the tooth profiles,

or cams, are designed so as to produce

a constant angular velocity ratio during

meshing, these are said to have

conjugate action.

One of these solutions is the

involute profile, which, with few

exceptions, is in universal use for

gear teeth.

Fuandamentals of Gear Design: gear ratio

When two gears are in mesh, their pitch circles roll on one another

without slipping. Then the pitch-line velocity must be constant.

Designate the pitch radii as and and the angular velocities as

and , respectively.

Gear ratio

Fuandamentals of Gear Design: gear drawing

gear layout

pressure angle

The angle is called the pressure

angle, and it usually has values of

20 or 25 degree, with the 20 degree

form most widely available.

Fuandamentals of Gear Design: gear drawing

Fuandamentals of Gear Design: gear drawing

Fuandamentals of Gear Design: important parameter

Fuandamentals of Gear Design: Gear Force Analysis

Fuandamentals of Gear Design: Gear Force Analysis