Page:Practical Treatise on Milling and Milling Machines.djvu/36

30 Efficiency. Production costs are of vital importance to the shop owner, and no one factor influences them to a much greater extent than the efficiency of the different machines employed. Where this is low, the amount of power consumed for which there is no apparent return is higher than it should be, with the result that the cost of production is increased. It is essential, therefore, that a high degree of efficiency may be attained in the milling machine, so that a maximum amount of work may be produced for the power consumed.

In order to obtain the highest degree of efficiency in milling machine construction, it is necessary that the utmost care be taken in designing the different parts, selecting materials, and in the quality of workmanship in building.

All parts must be proportioned in accordance with the functions they perform. They should be heavy enough to resist any stress that would tend to cramp operating movements. For instance, cylindrical shafts should be large enough in diameter to eliminate bending tendency, for this will cramp them in the bearings, thus interfering with their free revolution. Care must be taken, however, that the different parts are not proportioned so heavy that they will be cumbersome and thus produce excessive friction, which is detrimental to efficiency. It is here that the selection of materials is of

value, for often the weight of a part can be made lighter by the use of a material of greater strength.

The size of bearing surfaces is of especial importance to efficiency, as well as to permanent alignment and ridigity. It is between them that friction arises in operation, and in order to reduce this to a minimum, their proportions should be such that the parts may move freely under the heaviest load.

Correct alignments of bearing surfaces are as essential to efficiency as to accuracy, in order that the working parts may move freely. Any error in alignemnts tends to cramp or wedge the moving parts.

Simplicity of parts and the use of spur gearing as far as possible are also elements that contribute largely to high efficiency.