Spur, helical, bevel, worm gear and rack & pinion — design and production methods
Spur gears have straight teeth parallel to the axis. They are the simplest and most efficient gear type with 98-99% efficiency per mesh. Best for low to moderate speeds (up to 25 m/s pitch line velocity) where noise is not critical. Standard pressure angle: 20°. Common modules: 1-8 mm. Applications include gearboxes, conveyor drives, and machine tool feeds.
Helical gears have angled teeth (15-30° helix angle) that engage gradually, producing smoother and quieter operation than spur gears. Efficiency: 94-98%. Helical gears generate axial thrust requiring thrust bearings. Herringbone gears (double helical) cancel axial thrust. Applications: automotive transmissions, high-speed machinery, pumps.
Bevel gears transmit power between intersecting shafts (typically 90°). Straight bevel: simplest, moderate speed. Spiral bevel: curved teeth for smoother engagement, 30-40% higher load capacity. Hypoid gears: offset shafts (automotive differentials). AGMA accuracy Q8-Q12 for ground spiral bevel.
Worm gears achieve high reduction (5:1 to 100:1) in a single stage. Self-locking when lead angle below 5°. Efficiency: 40-95% depending on lead angle and lubrication. Bronze worm wheels mate with hardened steel worms for wear resistance. Applications: elevators, conveyor systems, valve actuators.
Rack and pinion converts rotary to linear motion. Precision ground rack achieves AGMA Q10-Q12 for CNC positioning. Backlash minimized with split rack or spring-loaded dual pinion designs. Applications: steering systems, linear actuators, CNC axes.
| Method | AGMA | Module | Best For |
|---|---|---|---|
| Hobbing | Q7-Q9 | up to 20 | Spur, helical, high volume |
| Shaping | Q6-Q8 | up to 12 | Internal gears, clusters |
| Grinding | Q10-Q14 | up to 8 | Hardened finishing |
| Broaching | Q8-Q10 | up to 6 | Internal splines |