Range of Usefulness

While in many shops the grinding machine is used only as a finishing tool on parts which require a special surface, or in which greater accuracy is required than is readily reached by the other machine tools, in modern work shops it is one of the large production factors. The work which comes to the grinding machine has usually been rough turned to an approximate diameter, but in many instances it has been found that the grinding machine will completely finish the piece of work from the rough stock at a lesser labor cost, doing its own roughing and finishing. This is especially true when long slender shafts are produced. Automobile crank shafts, for example, are commonly ground from the rough.

Fig. 325. Example of Steady Rests as Employed by Norton Grinding Company Courtesy of Norton Grinding Company, Worcester, Massachusetts.

Cylindrical Grinding

Producing cylinders of revolution is one of the more common uses to which grinding machines are put. This is usually accomplished by traversing a rotating abrasive wheel in contact with the rotating piece of work, as in Fig. 325. In this operation the rotating wheel can be made to feed along the length of the work by giving the work table a traversing motion along the bed of the machine. Some of the things to be noted in this machine are: (a) Its large wheel spindle with generous journals making it possible to use abrasive wheels large in diameter with broad faces; (b) the abrasive wheel bearing stand giving large spindle bearings and great rigidity; (c) a heavy traversing table with large bearing area upon the bed; (d) the work-supporting rests; and (e) the general massiveness of construction.

Fig. 326. Traverse Markings on Piece of Ground Work.

Wheel Speed

The peripheral or surface speed of the abrasive wheel is usually held pretty closely to 5500 linear feet per minute. While in some cases a wheel speed of 6500 feet per minute or as

Table XI. Revolutions Per Minute For Various Sizes Of Grinding Wheels To Give Peripheral Speed In Feet Per Minute

low as 4500 feet per minute may give good results, wheel speed does not in general practice vary much from the 5500 feet given. Table XI gives wheel speeds used in good practice.