CHAPTER V.

TURRET LATHES.

TURRET lathes are now made in all sizes, from the smallest, operating on minute watch screws and studs, to the largest, now suitable for the work in a general engineering workshop.

A representative type of machine for doing lathe work, particularly that class coming between in. and 2 in. diameter, and less than 24 in. long, is here given in detail: The Hartness Flat Turret Lathe, made by The Jones and Lamson Machine Co. (Fig. 86).

This lathe differs from other turret lathes principally in the form of its tool carriage and its tools; the turret is a flat circular plate, mounted on a low carriage, containing controlling mechanism.

An important feature lies in the manner the turret is connected to the carriage, and the carriage to the bed; for unless these are perfectly rigid, they will not afford perfect control of the cutting tools.

By referring to Fig. 87 it will be seen, in this enlarged view of the turret, that the base on which the various holders are secured is of large diameter. This is one of the distinct features of the machine. This base is scraped and padded to its seating on the carriage, and is secured by an annular gib.

In a similar manner the carriage is fitted to the vee's of the bed, but in this case the gibs pass under the outside edge of the bed, the breadth of this bridge from V to V being sufficient to form an unyielding support to the tools.

A further advantage is obtained by having the turret flat, since the indexing mechanism can be located with the index pin directly under the working tool so close as to permit no loss of motion between the tool and the locking pin.

Hartness Flat Turret Lathe.-The turret is turned automatically to each position the instant the tool clears the work on its backward travel, and it is so arranged that, by raising and lowering the trip screws near the centre of the turret, it may be turned to three, four, or five of the six places without making any other stop.

The power feed for the carriage is actuated by a worm shaft, the worm being held into the wheel by a latch which is disengaged by the feed stops.

There are six feed stops, each being independent and adjustable. These stops are notched, flat bars placed side by side on the top of the bed. The lever in Fig. 88 actuates the tool slide.

rigid a support as possible. Too much attention was formerly given

The headstock is necessarily squat to mate the turret, and is mounted on the bed, beneath which a box-shaped leg is placed, so as to give as

FIG. 86.-Hartness turret lathe.

to elegance. This, however, is not the case to-day, hence the solid and rigid appearance of the turret lathe above, which shows a proper balancing of parts.

The spindle is ground to size, and fitted in phosphor-bronze bearings. The spindle is made hollow to 2 in. diameter. It carries externally a cone and a large gear, called the front gear wheel (not seen in the figure, owing to the hood).

The back gear is placed below the cone in the head, and a triple gear is (sometimes) placed beneath this.

The regular back gear gives a 4 to 1 proportion, but the triple makes it 16 to 1.

The triple gear is used for all screws above 13 in. diameter, and in chucking work of large diameter.

The die carriage carries a die of any desired kind, and a pointer for shaping the end of a shaft or bolt, or the same tool may be used as a turner when reducing the stock.

The carriage is mounted on a sliding bar, and is arranged to swing into working position.

The head is driven through a triple friction counter shaft, on which shaft the pulleys are provided with extended bosses, so as to distribute equally the "pull of the belt" over the entire bearing on the shaft. The principal tool used is called the "turner" (Fig. 89). It consists of a frame holding a cutter, and a back rest or guide for the work. There are three forms of these "turners" in the most commonly used outfits, but the same distinctive feature may be found in each. The cutter in Fig. 90 is 1 in. by 1⁄2 in. rough steel. It is held in a pivoted tool-box which is accurately fitted to a frame, which in turn is firmly secured to the upper surface of the turret. The adjusting screw for effecting the size of the work acts on the tool block. Any size may be turned from o to 2 in. after the tool has been fitted.

A cam is provided for withdrawing the tool to prevent its marking the work in running off after having completed its cut. The top surface of the turret is only 3 in. distant from the centre of the work, thus making it possible to give the most rigid control of the cutting tool. The back rests are designed for quick setting, and may, by use of the latch, be withdrawn to pass over large diameters to begin a cut at any part of the work. The left-hand turner cuts with the backward motion of the lathe, and feeds from, instead of towards, the chuck. In the use of this "turner" both the cutter and back rests are withdrawn to pass over the work to reach its starting-point at the chuck. Since the left-hand turner starts its work very close to the chuck, slender work, being thus supported, may be accurately turned.

The cross slide (Fig. 88) is made in a compact form, and the sliding block, closely fitted and gibbed to its base, is bolted securely to the turret. A long lever and a small pinion and rack furnish means for feeding the cross slide tools. The tool holder will admit drills, reamers, taps (or holders to receive them). The taper turner is adapted for long tapers and other forms of varying diameters. These variations