In making a screw the following are the operations of this interesting and valuable machine: The bar is inserted through the open chuck and set against an end-gauge in the turret. The front tool in the carriage cuts the end of the bar; a turning-tool in the turret reduces it at one heavy cut to nearly the right size; a "sizer " brings the body to the exact size, and, an arm with an open die being brought down, the bolt is threaded; a solid die brings it to the exact size and cuts the full thread to the exact point desired; the front tool of the carriage chamfers off the end thread and the back one cuts off the bolt. The bolt being then reversed in the chuck, the top of the head is water-cut finished by a front tool in the carriage, this last operation being deferred until all the bolts of the lot are ready for it. This machine also taps nuts and makes a large variety of lathe-work.
The screw-machine exhibited in Figures to 7 (pi. is also made for the cheap and rapid manufacture of a very great variety of work of circular cross-section directly from bars of material such as steel, iron, brass, and hard rubber. Some samples of its work, consisting of screws, nuts, and studs, are shown in Figure 7. Bolts and set-screws with hexagonal or square heads are obtained by using stock of that cross-section. Small castings having holes and studs of various shapes and sizes to be finished can sometimes be worked up with great saving of time and labor over the lathe and drill-press. The speed with which these machines will turn out work depends upon the size and shape of the work and upon the material used. Screws such as are shown in Figure 7 (pl. 23), if made of iron, can be manufactured at the rate of from fifty to ninety per hour; if of brass, from seventy to one hundred per hour.
The machine (fig. 1) is operated by working three levers, the workman standing so that one is in front and one at each hand. The lever at the left operates the This mechanism, while the machine is run ning at full speed, so feeds forward the rod, from which the screw or other piece has been made, as to furnish just enough stock to make another. The handle at the right operates the turret-head, bringing successively six tools to act upon the stock. The centre handle operates the cross feed and governs the action of two tools, one usually a tool for chamfer ing, grooving, or and the other for cutting off the finished piece. In working wrought iron or steel a lubricant such as oil or soda water is used. To keep the tools sharp longer, so that the work will have a smoother and more accurate finish, a reservoir of oil is provided as shown in the cut. Into the basin-joining part of the frame of the machine is drained the oil, which is strained free from chips and dirt by running through wire gauze into the large tank, from which it can be drawn and used repeatedly, thus reducing the waste to a minimum. The workman starts the machine, adjusts the speed by shifting the belt to the correct step of the cone pulley, opens the valve of the oil-reservoir and adjusts its position until the oil drops at the right place, and gives a double oscillation to the wire-feed lever, by which the stock-rod is loosened, fed forward against a stop in the turret-head, and clamped.
Then at each double oscillation of the turret-head lever a new tool designed to do a special part of the work is presented to act upon the stock-rod, and by a double oscillation of the cross-feed lever the piece is chamfered or grooved and cut off, and the machine is ready to recommence the cycle.
Figures 2 and 3 show the wire-feed in detail. The steel spindle a (fig-. 2) is hollow, to allow the hollow rod b to pass freely through it, the hole through b being a little larger than the largest stock that the machine is designed to work. The conical part of the carefully tempered spring collet r fits into a hole ground to a corresponding taper in the hardened steel shell a'. Putting b in the spindle at A. so that the surfaces c' and b" coincide, and screwing d on the spindle at k, then, by pressing upon the end of the rod b', the conical parts of c and a' will coincide, forcing together the three jaws of the spring collet c, and clamping the stock-rod passing through it. Collets with different holes are required for different sized rods. The stock-rod has a continual tendency to go forward against c (jig. 3) because of the force transferred from a weight through the bronze chain a, over a small pulley to the piece b, which slides freely upon the rod e. By turning the disc upon b, various sized holes can be brought successively to a common centre, thus forming a very convenient bushing for different sizes of stock. By withdrawing the pressure from the rod b, the spring collet will retract, allowing the stock-rod to pass through until arrested by the stop in the turret-head, and by renewing the pressure the rod is again clamped, and the turret-head and cross-feed may proceed with their functions. To reciprocate these pressures while the machine is running, the rest of the mechanism shown in Figures 2 and 3 Cpl. 23) is necessary. In Figure 2, c fits loosely upon the spindle a, as shown in position in Figure 3. The piece (Jig. 2) is virtually a part of the rod b, the connection being made by screw-pins (f) passing through the slot in the spindle a, into holes (b') in the rod b Hinged to f are two tempered steel cam levers, which act against the bevelled surface of the hardened steel nut g, forcing the rod b forward; the nut g, after proper adjust ment, is held in position by a set-screw pressing a shoe against the threaded spindle; i is the fulcrum, which is screwed firmly into the frame of the machine. The steel yoke h has one surface of brass, which can be replaced when worn. The cone is fastened to the spindle, so as to allow adjustment with its axis by means of a nut (h), the thrust being taken in both directions by the front bearing intercepted by two hardened steel washers.