1. INST 6150 Communication Instruction and the Learning Process
INTRODUCTION TO GEARS

2. 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

3. GEARS
SPUR GEAR
WORM GEAR
BEVEL GEAR

4. GEAR 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

5. GEAR TERMINOLOGY OUTSIDE DIAMETER PITCH DIAMETER ROOT DIAMETER
DIAMETRAL PITCH
= TOOTH SIZE
CENTER DISTANCE

6. CENTER-TO-CENTER DISTANCE
MATING SPUR GEARS
TANGENT PITCH CIRCLES D2 D1
CENTER-TO-CENTER DISTANCE
D1 + D2 2
= CC DIST
COMPARE TOOTH SIZES

7. NUMBER OF TEETH PER INCH OF PITCH DIAMETER
DIAMETRAL PITCH
NUMBER OF TEETH PER INCH OF PITCH DIAMETER
18 TEETH
EXAMPLE:
Gear has 18 teeth and a pitch diameter of 2.25”.
2.25” =
P = =
18 TEETH
2.25 INCHES
? TEETH
1 INCH
Diametral Pitch (tooth size) = 18 teeth/2.25” = 8
P = 8

8. THE GEAR DESIGN FORMULANP
(or N = DP, or P = N/D)

9. GEAR RATIO Ratio = 9/18, or 1/2 Ratio = 25/18
Ratio of number of teeth on one gear to number of teeth on the mating gear
Ratio = 9/18, or 1/2
Ratio = 25/18

10. EXAMPLES 2.25” (2-1/4”) 25 teeth 4.50” (4-1/2”) 21/35, or 3/5
A 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

11. 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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