1. Gears

2. Gear Teeth Types
Involute (common)
Cycloidal
Mainly in watches

3. Involute Generation

4. Pressure Angle Mating gears must have the same pressure angle 14.5°
+Less bearing load
-Low bending strength
20°
+Less undercut
-High bearing load

5. Nomenclature

6. Diametral Pitch
Ratio of teeth to pitch diameter
‘Teeth per inch’

7. Spur Gears Teeth are parallel to the axis of the gear Advantages:
Cost
Ease of manufacture
Availability
Disadvantages
Only works with mating gear
Axis of each gear must be parallel

8. Helical Gears
Teeth are at an angle to the gear axis (usually 10° to 45°)
Advantages
Smooth and quiet due to gradual tooth engagements (up to 5,000 ft/min)
More tooth engagement allows for greater power transmission
Disadvantage
More expensive
Resulting axial thrust component

9. Helical Gear Videos Parallel Orientation
Cross Orientation

10. Worm Gears Gears that are 90° to each other Advantages Disadvantage
Quiet/smooth drive
Can transmit torque at right angles
No back driving
Good for positioning systems
Disadvantage
Most inefficient due to excessive friction (sliding)
Needs maintenance
Slower speed applications

11. Worms
Multiple starts
1,2, & 4 typical
Enveloped style

12. Double-Enveloped Worm Gears

13. Bevel Gears Gear axis at 90°, based on rolling cones Advantages
Right angle drives
Disadvantages
Get axial loading which complicates bearings and housings

14. Spiral Bevel Same advantage over bevel as helical had over spur gears
Teeth at helix angle
Very strong
Used in differentials

15. Racks Provide rotary to linear motion Various Materials Nylon Acetal
Steel
Stainless

16. Anti-Backlash Spur Gears
Reduces backlash in gear transmissions
Spring styles
Helical (shown)
Torsion

17. Shaft Attachment - Clamp
Does not mar shaft
Set gear at any orientation
Disadvantages
Limited torque
Two components

18. Shaft Attachment – Fairloc® Hub
Rigid coupling
Clamps circumferentially
One piece
Disadvantages
Limited torque
Expensive

19. Shaft Attachment – Hub w/ S.S.
Use two set screws
Align 90° from each other
Grind/machine flats on shaft
Disadvantage
Marring from screw
Screws loosen from vibration

20. Shaft Attachment - Keyed
Sacrificial component to limit torque
Variety of styles to choose (Feather Key shown)
Must design with standard sizes (gear must be broached)

21. Design Chart Categories of Gears Types of Gears Efficiency (%)
Parallel Axes Gears
Spur Gear
Spur Rack
Internal Gear
Helical Gear
Helical Rack
Double Helical Gear
98 to 99.5
Intersecting Axes Gears
Straight Bevel Gear
Spiral Bevel Gear
Zerol Gear
98 to 99
Nonparallel and Nonintersecting axes Gears
Worm Gear
Screw Gear
Hypoid Gear
30 to 90
70 to 95
96 to 98

22. Quality Class

23. For more information on gearing