SCREW MACHINES. The name screw machine is not properly descriptive of the class of machines to which it is applied. It does not well indicate many purposes for which they have come to be used, and yet it had been too long applied to be readily changed.
The name turret lathe is a more generic term, including the screw machines as a variety. (See LATHES.) Designed primarily for making screws, and use ful for this purpose whenever screws are not required in sufficient quantities to render entirely automatic machines preferable, screw machines are per Imps chiefly used in making a large variety of pieces from iron or steel bars, and in finishing castings or forg ings which may be held in a chuck while subjected to one or more opera tions. The full extent to which ex perience has shown that it is profitable to employ them for other purposes than for making screws may be judged from the fact that in the shops of the Brown & Sharpe Manufacturing Co. only one out of every eight is usually employed for this purpose. Three-eighths are ordinarily used in finishing studs, nuts, washers, bushings, pins, handles, etc., from round, square, or hexagonal stock ; while one half the machines are generally employed on small wheels, levers, or cams for sewing ma chines, or on small parts of machine tools.
Fig. 1 represents a new style of screw machine recently introduced by the Brown & Sharpe Manufacturing Co. The head is back-geared, and the change from belt speed to back gears is effected, without stopping the spindle, by a friction clutch which is practically positive in its action and will hold the full belt-power of the machine. The back gears are underneath the spindle-cone and are entirely enclosed. The gears on the cone are also enclosed. The cone has three steps. The turret is fed automatically or by hand, and has eight speeds. as each of the four speeds given by the feed cones may be varied by shifting a lever, so that without changing the belt the tools may be fed fast or slow for each stqp of the cone. This is a novel feature in sc::-ew machines. The turret is 9:1- in. in diameter. The movement of the turret-head slide is 91 in., and the extreme distance between the face-plate and the turret is 32 in. The length that can be drilled, or milled, without moving the turret-head slide bed is 6 in.
The Niles Screw Machine.—Fig. 2 illustrates a screw machine built by the Niles Tool Works, Hamilton, 0. The following is a detailed description : The chuck, A, is fast on the hollow arbor of the machine. B is a steadying chuck on the rear end of the arbor. C is an ordinary lathe car riage, fitted to slide on the bed and be operated by hand wheel, D, and a rack pinion.
Across t h is car riage, slides a tool rest, E, operated by a screw, and having two tool rests, one to the front and one to the rear of the work. This tool r e s t , instead of sliding directly in the carriage, as is the c a se with lathes, is mounted on an intermediate block which fits and slides in the carriage. This intermediate block is moved in and out, a short distance only, by means of a cam lever, G. An apron on the front end of the slide carries the lead-screw nut, II. When the lever cam is raised it brings the slide outward about half an inch, and the tool-rest, E, comes out with it, and at the same time the nut leaves the lead screw. The inward movement of the slide is always to the same point, thus engaging the lead screw and resetting the tool.
With this machine threads may be cut by adjusting a thread tool in the front tool-post, as in ordinary lathe practice, and at the end of the cut the cam lever serves to quickly with draw the tool and the lead-screw nut so that the carriage can be run back. The tool-rest is then advanced slightly and the new cut taken. By this means threads are out without any false motions, and may be cut up close to a shoulder. I is the lead screw. This screw does not extend to the head of the machine, but is short and is socketed into a shaft which runs to the head of the machine, and is driven by gearing. The lead screw is thus a plain shaft with a short, removable threaded end. The gearing is never changed. Different lead screws are used for different threads, thus permitting threads to be cut without running back. The lead screws are changed in an instant by removing knob, J. The lead-screw nut, II, is a sectional nut, double-ended, so that each nut will do for two pitches, by turning it end for end in the apron.