Turning and boring

Specialization in machine-tool manufacture has been developed to such a degree that there is need also (or treatises which specialize on different classes of tools and their application in modem practice. This book deals exclusively with the use of various types of turning and boring machines and their attachments, and is believed to be unusually complete. In addition to standard practice, it describes many special operations seldom or never presented in text-books. Very little space is given to mere descriptions of different types of machine tools, the principal purpose being to explain the use of the machine and the practical problems connected with its operation, rather than the constructional details. No attempt has been made to describe every machine or tool which might properly be included, but rather to deal with the more important and useful operations, especially those which illustrate general principles.

Readers of mechanical literature are familiar with Machinery's 25-cent Reference Books, of which one hundred and twenty-five different titles have been published during the past six years. Many subjects, however, cannot be adequately covered in all their phases in books of this size, and in response to a demand for more comprehensive and detailed treatments on the more important mechanical subjects, it has been deemed advisable to bring out a number of larger volumes, of which this is one. This work includes much of the material published in Machinery's Reference Books Nos. 91, 92 and 95, together with a great amount of additional information on modem boring and turning methods.

It is a pleasure to acknowledge our indebtedness to the manufacturers who generously supplied illustrations and data, including many interesting operations from actual practice. Much valuable information was also obtained from Machinery.

The standard "engine" lathe, which is the type commonly used by machinists for doing general work, is one of the most important tools in a machine shop, because it is adapted to a great variety of operations, such as turning all sorts of cylindrical and taper parts, boring "holes, cutting threads, etc. The illustration Fig. 1 shows a lathe which, in many respects, represents a typical design, and while some of the parts are arranged differently on other makes, the general construction is practically the same as on the machine illustrated.

The principal parts are the bed B, the headstock H, the tailstock T, and the carriage C. The headstock contains a spindle which is rotated by a belt that passes over the cone-pulley P, and this spindle rotates the work, which b usually held between pointed or conical centers h and hi in the headstock and tailstock, or in a chuck screwed onto the spindle instead of the faceplate F, The carriage C can be moved lengthwise along the bed by turning handle d, and it can also be moved by power, the movement being transmitted from the headstock spindle either through gears a, J, c, and lead-screw S, or by a belt operating on pulleys p and Pi, which drive the feed-rod R. The lead-screw 5 is used when cutting threads, and the feed-rod R for ordinary turning operations; in this way the wear on the lead-screw is reduced and its accuracy is preserved.

On the carriage, there is a cross-slide D which can be moved at right angles to the lathe bed by handle e, and on D there is an upper or compound slide E which can be swiveled to different positions. The tool t, that does the turning, is clamped to the upper slide, as shown, and it can be moved with relation to the work by the movement of the carriage C along the bed, or by moving slide D crosswise. The lengthwise movement is used to feed the tool along the work when turning, boring or cutting a screw, and the crosswise movement for facing the ends of shafts, etc., or for radial turning. When the tool is to be fed at an angle, other than at right angles to the bed, slide E, which can be set to the required angle, is used. The lengthwise and crosswise feeding movements can be effected by power, the lengthwise feed being engaged by tightening knob k, and the cross-feed by tightening knob I. The direction of either of these movements can also be reversed by shifting lever r. Ordinarily the carriage and slide are adjusted by hand to bring the tool into the proper position for turning to the required diameter, and then the power feed (operating in the desired direction) is engaged. The tailstock T can be clamped in different positions along the bed, to suit the length of the work, and its center h1 can be moved in or out for a short distance, when adjusting it to the work, by turning handle n.

As some metals are much harder than others, and as the diameters of parts to be turned also vary considerably, speed changes are necessary, because if the speed is excessive, the turning tool will become dull in too short a time. These speed changes (with a belt-driven lathe) are obtained by placing the driving belt on different steps of cone-pulley P, and also by the use of back-gears. The cone-pulley can be connected directly with the spindle or be disengaged from it by means of bolt m. When the pulley and spindle are connected, five speeds (with this particular lathe) are obtained by simply shifting the driving belt to different steps of the cone. When a slower speed is required than can be obtained with the belt on the largest step of the cone, the latter is disconnected from the spindle, and the back-gears G and d (shown in the plan view Fig. 2) are moved forward into mesh by turning handle O; the drive is then from cone-pulley P and gear L to gear G, and from gear G1 to the large gear J on the spindle. When driving through the back-gears, five more speed changes are obtained by shifting the position of the driving belt, as before. The fastest speed with the back-gears in mesh b somewhat slower than the slowest speed when driving direct or with the back-gears out of mesh; hence, with this particular lathe, a series of ten gradually in- creasing speeds is obtained. Changes of feed for the turning tool are also required, and these are obtained by shifting the belt operating on pulleys p and pi, to different-sized steps. On some lathes these feed changes are obtained through gears which can be shifted to give different ratios. Many lathes also have gears in the headstock for changing the speeds.


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