While the turret lathe in its perfected form is now a complete machine, the turret idea was first applied to engine lathes, and turret attachments are so universally popular that most of the lathe manufacturers now make them of dimensions suitable for their lathes, and attach them either to the lathe carriage or to a special bed which may be fastened to the lathe bed upon the removal of the tail-stock. A great variety of work may be done in the turret lathe, its principal rival being the automatic screw machine, whose economy lies principally in the fact that one operator may take care of a number of machines, each of these machines depending principally for their success upon the turret with its multiplicity of tools. And this idea of a turret carrying from four to eight tools is applied in a great variety of ways and to a large variety of machines on account of the ease with which any desired tool may be brought into a working position.

Fig. 24.   A Turret Lathe.

Fig. 24. - A Turret Lathe.

The head-stock of a turret lathe is made in several ways, from that of a plain head without back gears to one with a large variety of speeds, controlled by handles operating clutches, or friction driving devices, or both, and which may be operated while the machine is in motion. In some cases the head-stock is cast in one piece with the bed, in others fitted to it in a similar manner to that of an ordinary lathe. In still others the head has a transverse movement on the bed upon which it slides and its movement is easily controlled by the operator.

The turret is designed and constructed in a variety of forms, but principally either circular or hexagonal. It is mounted usually in a horizontal position, that is with its axis vertical, but still in some of the best machines, notably the Gisholt, it is pivoted in an inclined position, the object being to bring the long tools, made necessary by a large machine, up out of the way of the operator as they swing over the front of the machine.

In the smaller hand machines and in many of the turrets furnished upon ordinary engine lathes the turrets are rotated by hand as each change is required, but in the larger and more complete machines the sliding movement of the turret effects its rotation at the proper time near its extreme rear position.

There is no carriage, properly so called, upon a regular turret lathe. A cutting-off slide carrying two tool-posts, one in front and one in the rear, serve to carry a cutting-off tool and a facing tool, or one for doing forming within certain limits. The spindle being hollow, and a large part of the work of the turret lathe adapted for steel work being made direct from the bar, these tools are very useful.

Some turret lathes are particularly adapted for a large variety of chucking and forming work, which they perform very accurately and economically, an elaborate system of stops for the turret slide rendering them very efficient for this work.

The tools that may be used in a turret are almost without number, and the expert operator readily attacks the most complicated pieces and brings them out with excellent finish and with surprising accuracy. Internal and external threads are readily cut very true to size and with rapidity.

The screw machine is very closely allied to the turret lathe, so called, and the smaller sizes are fitted with what is called a "wire feed," which will automatically feed in the bar against the turret stop as soon as it is released by opening the chuck. This is in the hand screw machine. In the automatic screw machine all these movements are made automatically when once the machine is set up, the tools properly adjusted, the bar of stock once introduced and the machine started, and, barring accidents, the machine continues to run, dropping its work into a pan as it is completed and cut off, until the bar of stock is almost entirely used up.

Multiple spindle lathes are usually those having two spindles. These may be side by side for the purpose of performing two similar operations simultaneously; or one spindle may be considerably higher than the other, above the bed, thus giving two different capacities as to the diameter of work that can be accommodated on the same lathe; the larger swing being frequently used for boring or similar work. Notably of this type of lathe is that put in the market by J. J. McCabe.

While the general and well-marked types of lathes have been specified in this classification it must not be understood that the list is complete, as there are many special lathes, each of excellent mechanism and well adapted to the special work for which it is designed, that do not appear here, and that it is manifestly impossible to classify and describe in detail. Frequently they may be assigned to some one of the classes or sub-divisions here set forth, as all lathes must partake in some respect of the essential parts of those described.

Further on in this work many practical examples of the lathes described in this chapter will be found, their builders' names being given and their particular features pointed out and commented upon, and to them the reader is referred for the better examples of each of the classes enumerated in this chapter.