Читать книгу Mechanics: The Science of Machinery - A. Russell Bond - Страница 19

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After the slide rest invented by Maudsley, the next great improvement on the lathe was a turret head or a sort of turntable which carried a number of tools. The tools are arranged to come automatically into play one after the other. One tool, for instance, may cut a groove in the work, another finish the face of the work, another bore a hole in the piece and another tap the hole. In many cases, several of these operations are performed simultaneously. The head of the lathe is provided with a hollow spindle so that the work is automatically fed to the tools through this spindle, and as soon as one piece is finished, it is automatically cut off and the jaws of the clutch which holds the work, or stock as it is called, open automatically so that a new length may slide forward and be operated upon by the tools. The machine requires no attention once the tools have been set up to the proper angle, except that it must be kept supplied with bars of stock as they are consumed, and with a copious flow of lubricant on the tools. One operator can therefore take charge of a number of automatic lathes. All he does is to feed them; they do the rest.

The modern drill has also gone through a great many developments in order to speed up the work that it performs. When a casting is to have forty or fifty holes drilled and tapped in it, instead of following the old method of drilling each hole separately, a lot of separate drilling spindles are used, each fitted with a drill, and these are brought simultaneously into play. As many as fifty or sixty holes may be drilled at a single operation, and after the holes have been drilled, the drilling spindles move to one side to make way for the taps, which thread such of the holes as are to receive screws. By first setting the spindles in the proper position and then using jigs to locate the work properly under them, the assurance is had that every one of the scores of holes drilled will be accurately spaced apart and the spacing in every casting will be identical.

The multiple tool system is also used in milling machines in which a number of milling cutters either of the face or the end type come into play simultaneously upon a piece of work set in a suitable jig, and cut the piece with absolute precision, so that all castings will have faces accurately spaced apart and cut to exactly the same level.

It is by such methods as these that we are able to produce such large quantities of machinery at remarkably low cost. One of the most notable examples of such work was the development of the Liberty engine during the World War. This engine did not differ in principle from others built in Europe or in this country, but its design was carefully adapted to permit of interchangeable manufacture. No careful finish was used except where indispensable. Special jigs, tools, and fixtures were prepared. Ingenious wrinkles of American manufacture were introduced. All this consumed time, and great was the irritation of the general public. Under ordinary conditions, it would have taken years to have developed the Liberty engine to the manufacturing stage, but under the urgent stress of war, the whole work of design and preparation for manufacture was crowded into a few short months, and then Liberty engines began to be manufactured on a stupendous scale.