Introduction

A lever is a machine element, which is used to take mechanical advantage, that is, lift more load with little effort by turning about a fixed point called fulcrum (Plate 21.1). The ratio of the load to the effort is called Mechanical Advantage (MA). Levers are made of low alloy steel, mild steel, aluminium alloy, etc., using forging or casting methods.

Uses of Levers

Levers are used in different forms for many applications as given below:

• 1. Hand lever Its use can be seen in old railway signals, handle of hand press, etc.

• 2. Foot lever If the effort is more than 800 N, a foot pedal is used, as in a clutch pedal.

Types of Levers

The fulcrum of a lever can be in between two ends or at one end only. There are three possible variations in which the fulcrum, load, and effort can be applied (Figure 21.1). The arrows in the figure show the direction of the load/effort.

Difference between each type is given in Table 21.1.

A lever can be straight or bent (Figure 21.2). For a straight lever, load and effort are parallel as shown in Figure 21.2(a). For a bent lever, the load and effort can be inclined to each other as shown in Figure 21.2(b). If the bend is 90°, it is called a bell crank lever as shown in Figure 21.2(c). When an effort is applied at one end, the load is lifted at the other end. The amount of effort applied depends on the ratio of lengths L1 and L2.