Sprockets

Chain drives are used where positive action is required. The velocity is constant to some extent. Power is transmitted, in this case over a shorter distance than in the case of belt or rope drives. Chains are made up of rigid links and of various types. They are classified as:

• Hoisting chains
• Conveying or elevating chains.
• Power transmission chains.

The wheels over which chain runs are called sprocket wheels. These wheels have projecting teeth which fit the suitable recess in the links of the chain and thus enable a positive drive to be obtained.

The pitch of the chain is defined as the distance between a hinge center of one link to the corresponding hinge center of the adjacent link. The pitch circle diameter of the chain sprocket is the diameter of the circle on which the hinge centers lie, when the chain is wrapped round the sprocket.

Quality:

Sources of errors in manufacturing gears:
The gears (gear teeth) are generally made by one of the following two methods:

• Reproducing method , in which the cutting tool is formed involute cutter ,which forms the gear teeth profiles by reproducing the shape of the cutter itself. In this method, each tooth space is cut independently of the other tooth spaces.
• Generating method, in which the cutting tool (hob forms) the profiles of several teeth simultaneously during constant relative motion of the tool and bank.

The various sources of errors in the gear made by reproducing method can be due to

• incorrect profile on the cutting tool,
• incorrect positioning of the tool in relation to the work and
• incorrect indexing of the blank

The sources of error when gears are made by generating method are:

• Errors in the manufacture of the cutting tool
• Errors in positioning the tool in relation to the work and
• Errors in the relative motion of the tool and the blank during the generating operation.