INST 6150Communication Instruction and the Learning Process

INTRODUCTION TO GEARS

GEARS• Transmit motion between shafts

• Gear types

– Spur gears – parallel shafts – most common

– Bevel gears – perpendicular shafts

– Worm gears - perpendicular overlapping shafts

– Rack and pinion gears – convert circular motion to linear motion

GEARS

SPUR GEAR

WORM GEAR BEVEL

GEAR

GEAR TERMINOLOGYGEAR TERMINOLOGY• DIAMETRAL PITCH = “P” = Tooth size = # teeth per

inch of pitch diameter

• PITCH DIAMETER = “D” = Design diameter of gear if it were a smooth wheel

• NUMBER OF TEETH = “N” = Total number of teeth on any given gear. Must be a whole number.

• CENTER DISTANCE (Center-to-Center Distance) = Distance between centers of two mating gears

• GEAR RATIO = Ratio of number of teeth on one gear to number of teeth on the mating gear

GEAR TERMINOLOGY

PITCH DIAMETER

ROOT DIAMETER

CENTER DISTANCE

OUTSIDE DIAMETER

DIAMETRAL PITCH= TOOTH SIZE

MATING SPUR GEARS

CENTER-TO-CENTER

DISTANCE

TANGENT PITCH CIRCLES

D1 + D2 2

= CC DIST

D1

D2

COMPARE TOOTH SIZES

DIAMETRAL PITCHNUMBER OF TEETH PER INCH OF PITCH DIAMETER

EXAMPLE:

Gear has 18 teeth and a pitch diameter of 2.25”.

Diametral Pitch (tooth size) = 18 teeth/2.25” = 8

P = 8

P = = 18 TEETH

2.25 INCHES? TEETH

1 INCH2.25”

=

18 TEETH

THE GEAR DESIGN FORMULA

D = NP

(or N = DP, or P = N/D)

GEAR RATIORatio of number of teeth on one gear to

number of teeth on the mating gear

Ratio = 9/18, or 1/2 Ratio = 25/18

EXAMPLESA gear has 18 teeth (N) and a diametral pitch (P) of 8.

What is its pitch diameter (D) ? 2.25” (2-1/4”)

A gear has a pitch diameter (D) of 3.125” (3-1/8”) and a diametral pitch (P) of 8.

How many teeth (N) does it have? 25 teeth

Two mating gears have N = 30, P = 6, and N = 24, P = 6, respectively.

What is the center distance? 4.50” (4-1/2”)

Two mating gears have D = 3”, P = 7, and D = 5”, P = 7, respectively.

What is the gear ratio? 21/35, or 3/5

THE END

CREDITS

An I WANT MY M.A.W.W. production

Producer - Inverted-Bird Productions

Director - Dave “Deadeye” Manning

Technical Consultants - Don “The Wrench” Wilson

Kent “Flame” Walker

Special Effects - AustinWorks Inc.

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