The feed is positive, by a series of gears on the head-stock, with the usual change-gears for operating the lead screw, which is splined for driving the apron mechanism.

All sliding surfaces are hand scraped. Taper gibs, with adjusting screws, are used in the carriage and compound rest. The lead screw is made of special steel rolled for the purpose, 2 7/16 inches in diameter, and cut with 2 threads per inch. Pinions are of crucible steel and all nuts are case hardened. The countershaft has self-oiling boxes. The weight of the lathe with an 18-foot bed is 20,000 pounds, showing it to be a very massive machine for its capacity.

Prominent among the manufactures of heavy lathes is the Niles Tool Works who are also builders of heavy machine tools of other classes which have proven very popular on account of their good design, ample strength, generous proportions and excellent workmanship.

In Fig. 262 is shown one of their 72-inch swing lathes adapted for heavy work. This lathe is of somewhat similar design to the 50-inch New Haven Lathe shown in Fig. 261, but considerably heavier, not only in proportion to its larger swing but as generally considered, a more massive machine.

Fig. 262.   72 inch Swing Triple Geared Engine Lathe, built by the Niles Bement Pond Company (usually called a Niles Lathe).

Fig. 262. - 72-inch Swing Triple-Geared Engine Lathe, built by the Niles-Bement Pond Company (usually called a Niles Lathe).

The head spindle is very large and constructed of cast iron, as is usual with very large lathes. It is driven by means of the heavy internal gear on the face-plate only, as the cone runs upon a separate shaft provided for that purpose. The face-plate, which is very heavy and strongly braced by ample radial ribs on its rear side, is keyed to the head spindle and is not ordinarily removable.

The head-stock is triple geared by strong and heavy gears with wide faces. Thus fifteen speeds are provided for with ample space on the five-step cone for a wide driving belt.

The feeding and screw-cutting mechanism has three changes in the head-stock by means of a sliding pin which handles the connecting devices of the change gearing. The lead screw drives the feeding mechanism without using the threads cut upon it, through the medium of a short feed rod, located in the apron. This method avoids the use of a long feed rod with its many supports and the attendant inconvenience which is of much greater moment than in those used for the much larger and heavier lead screw.

The bed is very broad and massive and furnishes ample support for the heavy head-stock and its weighty appendages, the long and broad carriage with its compound rest of ample proportion, and the massive tail-stock, as well as for the four-jawed center rest which is furnished with this lathe.

The tail-stock is broad and heavy and carries a large tail spindle, moved by a system of miter and spur-gearing operated by a large hand wheel at the front side, and within convenient reach of the operator. The tail-stock is secured to the bed by four heavy bolts and a pawl engaging in a rack, cast to the bed on the center line.

While the tail-stock is unusually heavy it can be readily moved along the bed upon friction wheels, which are easily put in contact with the bed by means of levers provided for that purpose. The usual set-over device is provided for turning tapers.

These builders make much larger lathes upon the same design, and also upon special designs adapted for making large guns, ingot slicing, machining large forgings such as crank-shafts and the like. Of this character they build lathes swinging 90, 100, 110, and 120 inches, and of any length of bed that may be required.

An excellent example of heavy lathes for handling large forgings such as crank-shafts and the heavier castings coming within the capacity of such a machine is the 84-inch swing lathe, built by the Pond Machine Tool Company, now operating in connection with the Niles Company. It is shown in Fig. 263. It really swings 86 inches over the V's and 67 inches over the carriage.

The lathe is designed with ample provision for the immense strains to which such a lathe is subjected. As will be seen by an examination of the engraving, the head-stock is unusually massive, with liberal dimensions of the housings for the front and rear boxes of the main spindle, which is a matter of prime importance in any lathe, and more particularly in one designed for very heavy work.

Attention is also called to the massive construction of the compound rest, which is much stronger and more rigid proportionally than that of the 72-inch swing lathe, built by the Niles Works and shown in Fig. 262.

The carriage has a very long bearing on the bed and is made deep and heavy, as should be the case with this type of lathe. An objectionable feature is that of locating apron gears in front of the apron rather than between the apron plates, out of the way of the operator and beyond the reach of ordinary accidental injury to themselves. This should be avoided as far as possible in all lathes.

The tail-stock is of massive and rigid design, and well adapted for the heavy work expected of the lathe. It is provided with the geared device for moving the spindle, by which the hand wheel is placed at the front of the tail-stock and within easy reach of the operator. The base is secured to the bed by four bolts in the usual manner, while the dividing line between the base and the top casting carrying the spindle is placed high up and the top secured by four other bolts. By providing this double set of bolts the spindle may be set over for turning tapers by loosening the upper set of bolts only, leaving the main casting or base still firmly secured to the bed. Thus it is not necessary to block up or to remove the work from the lathe when setting for tapers, which is of considerable advantage, particularly on the heavy work which this lathe is designed to do.

Fig. 263.   82 inch Swing Triple Geared Engine Lathe, built by the Niles Bement Pond Company (usually called a Pond Lathe).

Fig. 263. - 82-inch Swing Triple-Geared Engine Lathe, built by the Niles-Bement-Pond Company (usually called a Pond Lathe).

In the builders' description of this lathe they say:

"With a 22-foot bed, this lathe will turn 8 feet 4 inches between centers. All its spindles are mounted in bronze bearings. The head spindle has upon it a thick flange of large diameter to which the face-plate is bolted in addition to being forced on. The cone has six wide belt steps of large diameter. It is mounted on the face-plate pinion shaft, is back geared and geared in to an internal gear on the face-plate, giving twenty-four changes of speed. The sliding head has a set-over for taper turning, held independently by four bolts, thus allowing adjustment without unclamping from the bed. It is provided with a pawl engaging a rack in the bed and is easily moved by gearing engaging a steel rack.

"The bed has three wide tracks, with the lead screw between them, bringing the line of strain nearly central, and is sufficiently wide to support the tool slide without the latter overhanging its front side when turning the largest diameters. The carriage has long bearings on the bed, is gibbed to the outside edges, and can be clamped when cross-feeding. It is provided with a tool slide having compound and swiveling movements; also with screw-cutting attachment and automatic friction longitudinal, cross and angular feeds.

"If either of the feeds, screw-cutting attachment, or rapid traverse of carriage and tool slides by power is in use, it locks out all others. The direction of the feeds may be changed at the carriage. Screw-cutting attachment and feeds are connected to the head spindle by three gears and a sliding key, giving three changes without changing gears. The carriage gearing is driven by a spline in the steel lead screw. The thread of the lead screw is used only for screw cutting. The gear engaging the feed rack can be disengaged when cutting screws, thus preventing uneven motion, caused by the revolution of the feed gearing."