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.
Figure 108 shows a design of tail-stock made by the Bridgford Machine Tool Works for their 42-inch swing lathe. It is of peculiar design and the base has the appearance of having been "built up in the sand," from the pattern designed for a lathe of much less swing. It is not a handsome design by any means, although it probably serves the purpose of supporting the tail spindle. It has a rack and pinion device for moving it along the bed. Its length on the bed is not as great as it should be, nor do the holding-down bolts seem large enough for a lathe of 42 inches swing. It has four bolts for holding down the base and a second set for securing the top part carrying the tail-spindle sleeve.
Fig. 108. - 42-inch Lathe Tail-Stock, built by Bridgford Machine Tool Works.
At A, Fig. 109 is one of Le Blond's favorite designs and which are used upon most of the lathes built by this concern. Its peculiar feature is the form of the tail-spindle sleeve with its very much enlarged front end. While it has a strange and unusual appearance, its form is based on sound principles of construction and is no doubt practical in giving more stability and rigidity to the tail center, which is a very desirable feature.
From the foregoing illustrations and descriptions the various features of tail-stocks, made by the different manufacturers, may be quite readily studied and their good and bad points duly considered, either for the purposes of designing a new lathe or for purchasing one suitable for the special line and class of work to be performed.
At B, Fig. 110, is the ordinary form of what is known as the "lever tail-stock," which is mostly used upon hand lathes. As its name implies, the tail spindle is moved lengthwise by a lever rather than a screw and hand wheel.
Fig. 109. - The Le Blond Form of Tail-Stock.
Fig. 110. -Lever Tail-Stock for Hand Lathes, built by the F. R. Reed Company.
This form offers facilities not possessed by the other form, or possessed in a less convenient form. In this spindle may be carried drills, reamers, etc., for use on light work held in a chuck. It may carry a small face-plate against which work may be held and drilled or reamed by a drill or reamer held in a chuck. It may carry an inside boring tool, and if made with a "set-over" device, such as is used on the tail-stock of an engine lathe, its usefulness is still further extended, particularly when working brass or other soft metals or materials. This design is by the F. E. Reed Company.
In addition to all the requirements thus far enumerated, which a lathe must possess in order to do good and heavy work, it must have a substantial carriage and compound rest or other tool-holding mechanism.
The carriage must support the compound rest on top and the apron hanging down at the front. Through the latter it must receive its driving mechanism as the lathe is now constituted. If we were to design a lathe with a view only to the theoretical requirements, we should, of course, put the device for moving it along the bed "on the cut," as near the cutting-tool as possible, and therefore the lead screw and feed-rod would be inside the bed and at some point between the front V and the central line. But we all know the practical objections to this and recognize it in lathe design.
There are a few points in the design of a good lathe carriage that it will be well to call attention to, since they are those that are frequently lost sight of, if we consider many of the present-day designs, and that the buyer of lathes as well as the machinist will do well to give attention to.
Figure 111 shows the design of an ordinary engine lathe carriage intended to be rigid and substantial. It has a wide center part, which is properly supported by the two ribs, thick and deep in the center. The only opening through it is one of moderate dimensions for permitting the chips to pass through.
The entire top is on one level so that large work to be bored may be bolted down upon it when the compound rest is removed for that purpose. Some lathe carriages have the dovetail, upon which the compound rest shoe runs, raised above the general level of the carriage. When work is to be bored it must rest upon this in the center while the sides are supported upon parallels with attendant inconvenience in bolting down rigidly. In this design there are four T-slots in front and two in the rear for the accommodation of bolts, while others may be passed through the chip opening in the center if necessary.
Fig. 111. - Engine Lathe Carriage Design.
The front wings of the carriage are broad, for the purpose of properly accommodating a full swing rest, an additional tool-post or other tool-holding device. The T-slots in the rear may serve a like purpose, or in conjunction with those in front serve for holding down any special attachment necessary.
The design of the bed is such as to furnish additional bearing surfaces for the carriage inside of the V's, the inner V's being replaced by flat surfaces, thus permitting the swing to be increased and the carriage very materially strengthened.