pieces are turned, screwed, &c., and then cut off in succession, is one of the chief reasons for the great success of automatics. In the ordinary lathe, the usual practice for turning pieces having irregular or shouldered shapes is to first forge them to the approximate shape, and then put between centres, and turn them up to the finished outlines. Instead in the automatics (and also in semi-automatics), a long parallel bar is passed through the hollow spindle, and sufficient of it left projecting at the front end to give the length of article required. The latter is then turned, and otherwise tooled until finished, after which it is cut off, and the bar fed through for another sequence of operations. The reduction of the

The arrangements of automatics in the shop are different from those of ordinary lathes, due to the fact of the bars of material projecting out so many feet. If all the machines were placed in line, the bars would foul the next machines. The lay-out shown in Fig. 162 is therefore adopted, the machines being angled slightly, so that the bars, shown as black lines on the diagram, pass behind the adjacent machines, and so enable them to be located closely together. The gangway between the two rows of machines enables the attendant to walk down, and inspect them, and to insert fresh material from the back gangways as required. The countershafts are not angled, but are placed parallel, as indicated by the dotted lines of

parallel bar necessarily means a certain waste of material in the form of cuttings, but this is counterbalanced by the saving of the cost of forging, and in the separate chucking which has otherwise to be done, if each piece is made as a separate length. The uniformity of sizes, and long life of the tools, is also induced by employing regular sizes of material. Separate forgings would be more irregular, and their scale would quickly ruin the tool edges.

Bars of iron, steel, brass, gun-metal, delta metal, &c., are employed for the production of pieces in this way, and the only duty of the attendant is to insert the length of bar in the spindle, after which the machine goes through all its operations in succession, repeating them until the material is used up.

centres; the belts twist themselves sufficiently to accommodate the want of parallelism between line and machine pulleys.

Although bar work has been, and is still the most valuable feature of automatic screw machine production, much has been done in recent years in the way of automatically handling castings, and forgings of irregular shapes which would not be economically produced from bar. Much of this has been deemed impossible to treat automatically, yet ingenious devices have been evolved for carrying the separate pieces in shutes or racks, feeding them singly to a chuck, which grips them until the tooling operations are finished. Many classes of wheels, gears, and gear blanks, collars, &c., are now treated in this fashion, with great economies

second by properly forming, tempering, and lubricating the tools. It must be remembered that the duty of the cutters is very light in many cases, and frequently a finishing tool follows a roughing one, so that the wear on the former being exceptionally slight, due to its light duties, enables it to cut correct sizes for a long while before needing re-setting. Automatics often run for several days, producing thousands of duplicate parts, without the tools being changed; on brass and other soft materials the endurance is of course longer than on hard steels, which are more severe on the tools, necessitating frequent sharpening.

Taking up a more detailed study, the named diagram, Fig. 163, of a standard type of machine by Alfred Herbert, Ltd., gives a good idea of the different parts, and their functions. This illustration shows the setting up for ordinary work, with standard cams, which lend themselves, by adjustments, to the production of various lengths and diameters of work, plain and shouldered, such as pins, and screws, which constitute the largest proportion of work done on automatics.

The drum on the extreme left serves to operate the chucking mechanism in the spindle, by the set of cam strips bolted to the surface of the drum; as the latter revolves, the strips in turn push the two pins seen immediately above the drum (see also the photograph, Fig. 164, Plate XIV.), and perform the releasing of the bar, its feeding forward, and re-gripping. The cams for loosening and tightening do not need adjustment after setting for a definite diameter of bar, but the cam for feeding to length (not visible) is easily altered to suit the distance it is required to push the rod through the. chuck, when batches of articles of varying lengths have to be produced.

Taking next the other large drum, underneath the turret, the cam strips on this serve to travel the turret slide up rapidly until the cutting starts, then more slowly to the end of the cut; a rapid backward movement then occurs, during which the turret is revolved by mechanism contained in the slide, bringing the next tool into line with the spindle, ready for a succeeding cut.

The cams for operating the cross slide are

attached to a disc only, since no longitudinal travel has to be imparted, which would necessitate the use of a long drum. The cams press against long pivoted levers, one of which is seen at the front. The other ends of these levers push the cross slide over, or pull it back. There are two tool-holders on this slide, one of which may carry a forming and the other a cutting-off tool, which are brought into action at appropriate intervals.

The large worm wheel seen to the right is for rotating the cam shaft. This wheel is driven by a worm through the medium of belt pulleys, which are seen in the photo of the end of a machine, Fig. 165, Plate XIV. Two different rates of speed are given to the cam shaft, which are obtained by the use of adjustable dogs on the disc at the extreme right (see also the end view, Fig. 165, Plate XIV.). It would obviously waste much time if the cam shaft revolved at a constant speed, which would have to suit the slowest operation involved in turning or screwing. The quick speed is therefore thrown in at certain intervals, as during the running back of the turret or cross slide and the feeding forward of bar. The method of throwing in the fast or slow speeds at the proper times is simple; a number of blocks or dogs are pinched with screws to the periphery of the disc at the end, and these strike a shipping lever, throwing in the fast or slow speed to the worm, driving the large worm wheel. The locations of the dogs around the disc determine the intervals at which the speeds are changed, and as the dogs can be shifted to any positions, the alterations can be timed exactly as desired.

These dogs are also utilised when it is desired to miss one or more operations in the turret. If, for instance, only two of the holes in the turret are carrying tools, the other three, or four, as the case may be, will only make idle movements, but it is still necessary that the turret slide shall go through the to-and-fro motions, in order to get the turret revolved. The movements for the empty holes are therefore performed at the high speed, to save time. This is done by setting shifting dogs to keep the rapid speed on until the idle cycle has been gone through, when another dog throws in the

Considering next the spindle-driving arrangements; in the Herbert machines the belt pulleys are not placed directly upon the spindle, as is usual in ordinary lathes, and in some other types of screw machines. The advantages claimed for the practice of putting the belt pulleys separately behind the head, and driving to the latter with spur gears (see Fig. 166, Plate

bearings. In the headstock shown in the photo, the two belt shifting forks seen in the left-hand top corner throw on fast or slow belt speeds when required, being actuated by cams from the cam shaft, one pulley being driven from the overhead at a higher rate than the other. By crossing one belt, a reverse motion. for tapping can be obtained. The use of the