Chapter twoDesign of Gears4IntroductionSpur gearsSpur gear tooth terminologyGear tooth forms Lewis equation for the strength of gear teethStandard modules and form factorsGear materials5The dynamic load, the limiting endurance beam strength load, and the limiting wear load to design a spur gearHelical gearsHelical gear tooth terminologyGear tooth formsVirtual or formative number of teeth6Lewis equation for the strength of gear teethStandard modules and form factorsThe dynamic load, the limiting endurance beam strength load, and the limiting wear load to design a helical gear7Bevel gearDifferent types of bevel gearsBevel gear terminologyLewis equation for strength of gear teethStandard modules, form factors, and virtual number of teeth8Dynamic, Endurance and The dynamic load, wear load and endurance tooth load to design a bevel gearWorm gear:Lewis equation for the strength of worm gear teethStandard modules and normal circular pitch 10Wear loads, Power rating and efficiency of a worm gear unit to design a worm gear

Week 4IntroductionSpur gearsSpur gear tooth terminologyGear tooth forms Lewis equation for the strength of gear teethStandard modules and form factorsGear materials

IntroductionGears are defined as toothed wheels, which transmit power and motion from one shaft to another by means of successive engagement of teethThe centre distance between the shafts is relatively small.2. It can transmit very large powerIt is a positive, and the velocity ratio remains constant.4. It can transmit motion at a very low velocity.

CLASSIFICATION OF GEARSFour groups:1) Spur Gears2) Helical gears

3) Bevel gears 4) Worm Gears

Law of GearingThe common normal at the point of contact between a pair of teeth must always pass through the pitch point

This is fundamental condition which must be satisfied while designing the profiles for the teeth of gear wheels.

Gear Materials

The material used for the manufacture of gears depends upon the strength and service conditions like wear, noise etc.

The gears may be manufactured from metallic or non-metallic materials.

The metallic gears with cut teeth are commercially obtainable in cast iron, steel and bronze. The nonmetallic materials like wood, rawhide, compressed paper and synthetic resins like nylon are used for gears, especially for reducing noise.

The cast iron is widely used for the manufacture of gears due to its good wearing properties, excellent machinability and ease of producing complicated shapes by casting method. The cast iron gears with cut teeth may be employed, where smooth action is not important.

The steel is used for high strength gears and steel may be plain carbon steel or alloy steel. The steel gears are usually heat treated in order to combine properly the toughness and tooth hardness.

Design Considerations for a Gear Drive

Homework Problem

Helical GearsA helical gear has teeth in form of helix around the gear. Two such gears may be used to connect two parallel shafts in place of spur gears. The helixes may be right handed on one gear and left handed on the other. The pitch surfaces are cylindrical as in spur gearing, but the teeth instead of being parallel to the axis, wind around the cylinders helically like screw threads. The teeth of helical gears with parallel axis have line contact, as in spur gearing.This provides gradual engagement and continuous contact of the engaging teeth. Hence helical gears give smooth drive with a high efficiency of transmission.

Bevel Gears

Pitch Angle for Bevel Gears