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.
The carriage is scraped to the full bearing of its entire length on the V's and is gibbed at both back and front to the outside of the bed. It is made deep and strong and has power lateral and cross feeds in all sizes of lathes.
Fig. 247. - Apron of the 16-inch Bradford Lathe.
This company make a variety of different types of lathes and attachments for them, which will be illustrated and described under appropriate headings and later on in these chapters.
The American Tool Works Company is a comparatively new concern and is, therefore, unhampered by old traditions and the somewhat inconvenient inheritance which burdens some of the older manufacturers, that is, an accumulation of old designs and older patterns.
In Fig. 248 is given an illustration of their 20-inch swing engine lathe, which has a rigid and strong appearance and mechanical design that speaks well for its builders, who have evidently intended to make a lathe of exceptional productive capacity, and ability to stand up to the heavy duty now imposed on such tools by the use of high-speed tool steels and coarse feeds for the rapid reduction of the material.
The head-stock is massive and of a symmetrically rounded form. The cone has five steps and takes a belt of rather more than the usual width. The spindle is of high carbon special steel and accurately ground, bored out with a large hole, and runs in a good quality of anti-friction metal boxes, provided with automatic ring oilers.
The carriage is proportionately heavy and strong, liberally provided with T-slots, and has a flat top for convenience of bolting down work to be bored or otherwise machined. The bearings upon the V's extend the entire length of the carriage. The compound rest is broad and strong and well fitted with hand-scraped surfaces, as are all the sliding contacts of the lathe.
Fig. 248. - 20-inch Swing Engine Lathe built by the American Tool Works Company.
The bed is of deep box girder section. The webs are well tied together with cross bars of box form, making the bed very strong and rigid. It is of the "drop-V" pattern, which gives an additional swing of about 2 1/2 inches. The V's are far apart and the front tail-stock way is flat, which, in connection with the drop-V construction, renders it possible to add an unusual amount of metal to the bridge of the carriage, thus insuring unusual stiffness and rigidity.
The lead screw is located within the bed and imparts motion to the carriage directly under the cutting-tool. This construction obviates much of the tendency to twist or lift the carriage off its seat so common in even the best modern lathes where the lead screw is located on the outside of the bed and pulls the carriage by its connection with the apron. The apron is tongued and grooved to the carriage and secured by large and substantial screws. All studs are of tool steel, hardened and ground. All pinions are of steel and are bushed with bronze. All gears are of wide face and coarse pitch. The reverse feeds are not by means of bevel gear and two bevel pinions, as in most modern lathes, but by tumbler gears, suitably controlled at the front of the apron. It is well known that bevel gears and pinions are broken by slipping in and out of engagement when running. In this lathe the bevel gear and pinions are constantly engaged, and therefore can be cut theoretically correct and run in close working contact. A separate splined rod is provided for driving the apron mechanism, thus obviating the necessity of splining the lead screw, as it is well known that no screw will remain true after splining. The screw is therefore simply and solely used for thread cutting and as a further precaution it is placed inside of the bed and has no connection whatever with the apron or its mechanism.
The carriage slides, both upper and lower, are fitted with taper gibs which are tongued and grooved into the sides, so that no amount of strain will disturb them. These gibs are adjusted by a convenient screw at each end. The feed screws are provided with micrometer dials.
The thread-cutting mechanism is exceptionally well made. All shafts are of high carbon steel and accurately ground. The four-speed gear box is mounted on the head end of the bed, and by means of clutch members, operated by suitable knobs conveniently located, four changes are instantly obtainable. This, in connection with a cone of eleven gears, mounted on the inside of the bed, any one of which can be engaged instantly by means of a sliding tumbler gear, makes forty four changes obtainable, without removing a gear. The index is well arranged and comparatively simple to understand, so that the practical operation of this mechanism is more simple and easy than many of the rapid change gear devices.
The workmanship on these lathes is unusually good, and this applies not only to the smoothness and fineness of finished surfaces, but what is of still more importance, to good fits. That the makers have endeavored to make a particularly good lathe is evident, whatever may be our opinion of the design of the "disc of gears" introduced into the rapid change gear design.
The Springfield Machine Tool Company make a variety of engine lathes and special lathes for various purposes that are unique in some respects, and very serviceable lathes for a large class of manufacturing work.
Fig. 249. - 16-inch Swing Engine Lathe built by the Springfield Machine Tool Company.
Their 16-inch engine lathe is shown in Fig. 249, which is equipped with rapid change gear device, reverse motion operated at the apron, automatic stop for turning and thread cutting, and provided with a friction-geared head spindle.