# Gear Geometry 240

This class discusses the geometry and design of gears commonly used in industry. Includes an Interactive Lab.

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## Class Details

Class Name:
Gear Geometry 240
Description:
This class discusses the geometry and design of gears commonly used in industry. Includes an Interactive Lab.
Version:
1.0
Difficulty:
Intermediate
Number of Lessons:
14
Spanish
Related 2.0 Class:
Gear Geometry 261

## Class Outline

• Objectives
• What Is a Gear?
• Using Gears to Alter Speed and Torque
• Using Gears to Change Direction of Motion
• Parts of a Gear Tooth
• Involute Curve
• Involute Gears
• Pitch Circle
• Gear Pitch
• Gear Tooth Geometry
• Clearance and Backlash
• Gear Specifications and Standards
• Gear Design Variations
• Summary

## Objectives

• List advantages of using gears for power transmission.
• Describe how gears are used to alter speed and torque.
• Describe how gears are used to change direction of motion.
• Identify parts of a gear tooth.
• Describe features of an involute curve.
• Explain why gears are designed with the involute profile.
• Describe a gear's pitch circle.
• Distinguish between circular pitch and diametral pitch.
• Identify tooth specifications used in gear tooth geometry.
• Distinguish between clearance and backlash.
• Describe how gears are standardized.
• Identify gear designs that vary from the spur gear.

## Certifications

MSSC
• MSSC Maintenance Awareness

## Glossary

Vocabulary Term Definition
addendum The distance between the top land of the gear tooth and the pitch circle.
addendum circle An imaginary circle that passes through the addendums of the gear teeth.
American Gear Manufacturers Association An organization of gear manufacturers that creates standards for gears manufactured in the United States, abbreviated as AGMA.
axis An imaginary straight line that passes through the center of an object. A gear may have an opening at its axis through which a shaft can be inserted.
backlash The distance by which the tooth space of one gear exceeds the tooth thickness of the meshing gear.
base circle In an involute curve, the circle from which the curve is unwound in a spiral shape.
belt drive system A system consisting of a belt and at least two fixed pulleys that is used to transmit motion.
bevel gear A type of gear with cone-shaped teeth cut at an angle. Bevel gears are often used in angular gear trains.
bottom land The bottom part of the gear tooth, which extends below the pitch circle.
chain drive system A system consisting of a chain and sprockets that is used to transmit motion.
circular pitch The distance from a point on one gear tooth to the corresponding point on the next gear tooth, measured along the pitch circle.
circular thickness The thickness of a gear tooth, measured on the pitch circle.
clearance The distance between the top land of a gear tooth and the bottom land of the tooth it meshes with on the mating gear.
coarse-pitch gear A gear with a diametral pitch of 19 or less. The teeth of coarse-pitch gears are larger and have greater spaces between them than the teeth of fine-pitch gears.
conjugate Intersecting with two involute profiles that transmit motion uniformly from one gear to the next.
contact ratio A ratio that represents the average number of gear tooth pairs in contact on a pair of meshing gears. Greater contact ratios can create smoother operation.
dedendum The distance between the bottom land of the gear tooth and the pitch circle.
dedendum circle An imaginary circle that passes through the dedendums of the gear teeth.
diametral pitch The number of teeth given per inch of a gear's pitch diameter. Diametral pitch is the most common method of classifying gears.
drive gear The gear that receives energy from a power source, such as an electric motor. A drive gear transmits power to a meshing driven gear to perform work.
driven gear The gear that receives motion from the drive gear on a machine. Driven gears often turn tools or components.
efficiency A measure of the work output of a system versus the total work input.
face The surface of a gear tooth located between the pitch circle and the addendum circle.
fine-pitch gear A gear with a diametral pitch of 20 or greater. The teeth of fine-pitch gears are smaller and closer together than the teeth of coarse-pitch gears.
flank The surface of a gear tooth located between the pitch circle and the dedendum circle.
friction A force that resists motion between two objects that are in contact with each other.
gear A round or cylindrical mechanical component with teeth, used to transmit power. Gears are designed to intersect with one another and can alter the speed, torque, or direction of mechanical energy.
gear ratio The relationship between the number of teeth on two meshing gears used to transmit motion. The gear ratio reflects the change in mechanical advantage resulting from the gears.
gear reduction A gear ratio used to decrease the speed and increase the torque of mechanical energy. A 1:2 gear ratio is an example of a gear reduction.
herringbone gear A type of gear that has angled teeth in the shape of a letter "V." Herringbone gears resist side loading but are expensive to produce.
idler gear A gear that is used to keep the direction of motion consistent between a drive gear and a driven gear.
involute curve The path determined by tracing a point on a line that is unwound from a circle.
involute gear A gear that is designed with an involute profile to transmit motion uniformly. Most gears used today are involute gears.
linear motion Motion that takes place along a straight line. Mechanical energy can take the form of rotary or linear motion.
meshing The action of interlocking with another object. Meshing gears are used to transmit mechanical energy.
nomenclature A system of naming objects in a given category. Gear nomenclature refers to the terminology used to describe and specify gears.
pinion A circular gear used in a rack and pinion system to produce linear motion. As the pinion turns, the flat rack slides in a linear direction.
pitch A property used to classify gears. Gears can be classified by circular pitch or diametral pitch, but the diametral pitch method is the most common.
pitch circle An imaginary circle on a gear that divides the gear teeth into top lands and bottom lands, and into addendums and dedendums. The pitch circles of two gears in correct mesh contact each other at the pitch point.
pitch diameter The diameter of a gear's pitch circle. A gear's pitch diameter can be determined by measuring from the top of one gear tooth to the bottom of the opposite gear tooth.
pitch point The point at which the pitch circles of two gears are in contact with each other at a single point.
pressure angle The angle made by the sides of a gear tooth as they incline toward the top of the gear.
rack A flat bar with teeth used in a rack and pinion system to produce linear motion. As the circular pinion turns, the rack slides in a linear direction.
rack and pinion A pair of gears used to convert rotary motion into linear motion. A rack and pinion consists of a circular gear, or pinion, that meshes with a flat-toothed bar, or rack.
rotary motion Spinning or turning motion that takes place around an axis, without a change in linear position.
shaft A cylindrical bar used to support rotating components or to transmit rotation in a mechanical system.
speed The amount of distance an object travels in a given period of time. Speed is used to measure both linear and rotational movement.
spur gear A type of gear that has straight, flat-topped teeth set parallel to the shaft. Spur gears are the most common industrial gears.
tangent In gear geometry, the point at which the pitch circles of two gears are in contact with each other at a single point. The tangent is also called the pitch point.
top land The top part of a gear tooth, which extends above the pitch circle.
torque A force that produces rotation. Power transmission components are often used to increase or decrease torque.
wear The gradual removal of material on a surface caused by contact between surface asperities.
whole depth Either the total height of a gear tooth, or the total depth of the tooth space.
working depth A measurement of how deeply a gear tooth extends into the tooth space of the mating gear.