Drive Gear Lab Report

INTRODUCTION

1.1 Gear and its utility.
When power is to be transmitted from one point to other point in a machine then two types of machine elements can be used. One is gear or toothed wheel and other is belt drive. But in belt drive slip is very much considerable negative phenomenon and due to this constant velocity ratio cannot be achieved. For this reason gear is preferred over belt drive where constant velocity ratio is needed especially for precision machine.
When friction between two tangentially mating wheels is sufficient the power transmitted is kinematically equivalent with the power transmitted by a pair of gears. For a mating tangential wheel, the driven wheel will rotate as long as driving wheel does not experience frictional

Thus the friction drive is not a positive drive, beyond certain limit. In early days, friction discs were used for transmitting the power from one shaft to another shaft. In such a case, the power transmission capacity depends on friction between surfaces of two discs. Therefore, this method is not suitable for transmitting higher power as slip occurs between the discs. In order to transmit a definite power from one shaft to another, the projections on one disc and recesses on another disc can be made which can mesh with each other. This leads to the formation of teeth on both discs and the discs with teeth on their periphery are known as “Gears”. In a gear motion is transmitted by successive engagement of teeth by acting like a lever. Due to primary rolling contact between teeth gears’ efficiency are very high (95%) and acts as a positive transmission element. Instead of rolling contact between teeth, gear exerts high force due to positive engagement between teeth. So gear’s motion does not depend on the rolling friction between teeth and works well even when friction is

As spur gear makes noise and vibration, it is used for low speed applications whereas helical gears are used for comparatively high speed applications as helical gears work quietly. In this context it is worthy to mention over here that high speed means peripheral speed more than 25m/s.
In heliacal gear, as profile curves around the base cylinder at helix angle, one axial thrust component is generated along with the radial component and tangential component of resultant load. This is the main disadvantage of a helical gear. Because this axial force will try to disengage the mating gears.
Double helical
There is a special type of helical gear consisting of two helical gears with the opposite hand of helix as shown in figure 1.4 below. This is known as Herringbone gear or Double-Helix gear. The construction results in equal and opposite thrust load on the shaft. Herringbone gears are used only for parallel shafts.

Fig1.4: Herringbone gears (or double-helical gears)

Rack and