Page:Practical Treatise on Milling and Milling Machines.djvu/45

Rh the driving shaft. In leveling and aligning the counter-shaft, it is the practice to insert the bare shaft in its boxes and take measurements from it. It is afterward removed, the pulleys put on and then replaced in its bearings. When the hangers are securely tightened, the shaft should revolve freely. About an eighth of an inch end play is desirable on a counter-shaft. This can be obtained when placing the hangers.

The shipper handles are most convenient when they come within easy reach from the left front side of the machine, as this is the position commonly taken by the workman to watch the operation.

Counter-shaft bearings are lubricated in various ways. In our particular type the oil is raised from reservoirs in each hanger by means of rope wicks as shown in Fig. 2.

As a rule it is not necessary to draw off and replace the oil in counter-shaft reservoirs at very frequent intervals if a good machinery oil is used. If the reservoirs are thoroughly cleaned and filled with fresh oil once every year or so they rarely need much attention. It is good practice, however, to put in a little oil every three or four months in order to insure maintaining the proper level.

The arrangement of a three-friction pulley counter-shaft is shown in Fig. 1. Its operation is as follows: A movement of the shipper to the right from the position in which it is shown, causes thimble A to spread the friction levers or engage pulley C.  Throwing the shipper to the left until thimble A is about central between uplleys C and E, causes thimble B to spread the friction levers or engage pulley D.  A further movement of the shipper to the left allows the levers of pulley D to slip over onto the smaller diameter of thimble B, disengaging the clutch o fthis pulley; at the same time thimble A spreads the levers engaging pulley E.

Diameter of Pulley on Driving Shaft. To find the diameter of pulley required on the driving shaft for driving the counter-shaft at a given speed, multiply the required speed of the countershaft in revolutions per minute by the diameter in inches of the pulley on same, and divide the product by the revolutions per minute