This section is from the book "Lathe Design, Construction And Operation, With Practical Examples Of The Lathe Work", by Oscar E. Perrigo. Also available from Amazon: Lathe Design: Construction And Operation.
Experience has demonstrated that with proper care on the part of the operator a box constructed in this manner will last for a very long time, and, if properly lubricated, that the babbitt metal will soon "glace" over and form one of the best bearing surfaces obtainable. The spindle is bored out to 1 1/4 inches. The driving-cone is of five steps, the largest being 12 inches and is adapted for a 2|-inch belt. The carriage is of ample strength and has a long bearing upon the bed, and supports a very substantial compound rest. The carriage is gibbed to the outside of the bed both back and front. The apron is of ample dimensions, so as to afford space for large and strong operating parts, which are few in number and simple in construction.
The feeds include an independent rod and patent friction feed. Combined gear and belt feeds are furnished and also an automatic stop motion in connection with either type of feed. There is also provided a simple belt tightener device. The belt feeds are from 25 to 95 per inch inclusive. When a geared feed is wanted the belt can be removed and the feed rod connected with an intermediate gear. Then by changing the gears upon the feed stud of the head-stock, feeds may be obtained from 12 to 125 per inch, inclusive. Even this range of feeds seems rather fine for modern methods of work. The lathe will cut seventeen different threads from 2 to 20 per inch, inclusive. The rack and rack pinion are of steel and capable of disengagement when regular turning feeds only are required. An "offset" tail-stock is furnished.
The net weight of one of these lathes with an 8-foot bed is 3,080 pounds, by which it will be seen that ample weight is provided to obtain a strong and rigid machine. The countershaft is furnished with patent friction pulleys which can be oiled while running, and with self-oiling boxes which will run six months with one oiling, and requiring no further attention.
This company make a variety of different styles and types of lathes, as well as attachments and accessories, which will be found described and illustrated further on in these pages and under their appropriate headings. The reader is referred to them for further information.
Fig. 226. - 14-inch Swing Engine Lathe built by the Pratt & Whitney Company.
Another of the old and reliable lathe building establishments is that of the Pratt & Whitney Company, which has for many years enjoyed an enviable reputation as makers of fine machine tools. While they have been progressive, and have brought out many valuable improvements they have never been prone to exploit mechanical fads, or to put on the market comparatively untried devices of the newest kind suggested by enthusiasts who imagined them capable of marvelous results. They have nearly always produced machines well and carefully designed, and constructed of good material and of excellent workmanship.
While the product of the company has been large and varied, a great deal of attention has been given to producing good lathes, a sample of which is given in Fig. 226, which is a 14-inch swing engine lathe of recent design. While rated as a 14-inch lathe it swings nearly 16 inches over the bed, and, as a lathe of that capacity, is heavy and strong, with a deep and heavy bed supported on their well-known design of legs rather than cabinets. Still the net weight of a 6-foot bed lathe is 2,200, which is very heavy for a lathe of these dimensions.
The apron is shown in Fig. 227, in which it will be seen that it is of very strong construction, being made with two plates whereby the shafts have a support at both ends. The feed rod is carried in double boxes in which are carried right and left worms, engaging the two worm-gears which operate the feed mechanism. While the use of worms and worm-gears in a lathe apron cannot be commended, and the difficulties which most builders have found with them, have caused their use to be discontinued, this company still retain them and by very good construction render them successful.
Fig. 227. - Apron of the Pratt & Whitney Lathe.
The lead screw nut is well supported to stand the strain to which it is put, and altogether the apron is an excellent specimen of good material and workmanship. The double plates are a feature that ought to be adopted in all lathe aprons as it adds much to the strength of the mechanism, holds the shafts well in line by supporting them at both ends, and materially increases the wearing qualities of the various parts.
While the various sizes as have been given for the lathes of other builders are not at hand, it may be said that all bearings have more than usual diameter and length and the boxes are accurately scraped to fit ground journals. The head-stock is massive and well designed and provided with a five-step cone pulley.
The feed gearing is operated by a two-step cone, but has compound gearing by which a large variety of feeds may be produced. The thread-cutting mechanism provides for cutting from 2 to 92 threads per inch, and by the use of the translating gears will cut all the usual metric threads.
Other lathes of different dimensions and types will be illustrated and described later on in this book and under their appropriate headings. For information of this kind the reader is referred to the chapters on these subjects.
The name of Flather has been so long and so intimately identified with the invention and the building of machine tools, that in the development of any type of them we naturally look for those bearing this name. In the improvements of the rapid change gear devices we find the names of Edward, Joseph, Herbert, and Ernest, each of whom have added something new to the "state of the art." In Fig. 228 is given a front elevation of 18-inch swing "quick change gear lathe," which seems designed to meet the latest requirements, and which is powerful, strong and rigid, and combines a reasonable degree of simplicity with accuracy, ease of operation, good workmanship and material. The head-stock and tail-stock are fitted to the bed with a V at the rear and a flat track in front, thus permitting the cross bridge of the carriage to be deep and strong. As will be seen in the engraving, the head-stock is heavy and strong with ample housings for the main spindle bearings, which are lined with genuine babbitt metal, cast solid in the head-stock, compressed, then bored out and scraped to an accurate fit for the ground journals of the spindle, which is made of hammered crucible steel. Its front bearing is 3 inches in diameter and 4f inches long. The bore of the spindle is 1 1/2 inches.
Fig. 228. - 18-inch Swing Quick Change Gear Engine Lathe, built by Flather & Co.