3 Principal Parts of Turret Lathe | Machine Tools | Industrial Engineering

The following points highlight the three principal parts of turret lathe. The parts are: 1. Head Stock 2. Carriage or Cross-Slide 3. Turret.

Part # 1. Head Stock:

The head stock of a turret lathe is similar to that of an engine lathe, but larger and heavies in construction with a wider range of speeds. Normally the range of speeds varies from 30 to 2000 r.p.m.

One of the chief characteristics of turret head stock is the provision for rapid stopping, starting and speed changing in order that the maximum advantage shall be taken by the operator, of the most advantageous cutting speed for any job and at the same time to minimise the loss of time in speed changing, stopping and starting.

On small, simple Capstan lathes where the machine is engaged for long periods on the same or narrow range of work diameters, frequent changing of speeds is unnecessary and for simplicity a three step ungeared cone-pulley drive is employed.

This may be driven by a special counter-shaft arranged so that starting, stopping and reversing are actuated by foot pedals connected to the belt shifting arrangement. The operator of one of these machines, therefore, has the hands always free to operate the levers concerned with feeding and cutting of work.

There are two principle types of head stocks:

i. An electric head, in which a multiple-speed motor is mounted directly on the head-stock, and

ii. All geared head which gives a wider range of speeds and allows heavier cuts to be taken.

Pilot bar or an over arm support is another feature of this machine. It is provided on the top of head stock and thus gives rigidity and piloting for the tool for accurate working particularly when heavier cuts are taken.

Part # 2. Carriage or Cross-Slide:

The cross-slide unit, on which the tools are mounted for facing, forming and cutting off is somewhat different in construction from tool-post and carriage arrangement used on lathes.

It is made up of four principle parts:

i. Cross-Slide,

ii. Square turret,

iii. Carriage,

iv. Apron.

In some of the turret lathes cross-slide is supported on the front and lower front ways, permitting more swing clearance for the work. This arrangement is frequently utilised on saddle-type machines, which are to be used for large diameter chucking work.

In another arrangement, the cross-slide is mounted on both upper bed-ways and is further supported by the lower-ways. This type of arrangement is used in those machines which are used for bar work and in processes where a large swing clearance is not necessary. An advantage of this type is the added tool post in the rear, frequently used for cutting off operations.

On the top of cross-slide is mounted rear and front end square turret, each of them being capable of holding four tools in readiness for use. If several different tools are required, they are set up in sequence and can be quickly indexed and locked in correct working position. In order to have duplicating cuts, the slide is provided either with a positive stop or feed trip.

The rear ends of the stops control the depth of cut of the rear turret tools, while the front ends of the stops control the depth of cut of the from tools. Dogs on the side of the cross-slide engage these stops to regulate the cross-slide travel.

The carriage has hand wheels for hand feed, either longitudinal or cross. Besides hand feed, power feed (either rapid or slow) can be engaged by moving a lever which pushes a spring actuated pin inward. When the trip dogs hit the feed stops, they release this pin which drops the feed lever to off position and stops the travel.

The feed can be reversed in order to have the tool movement in either direction. For exceedingly accurate work, a cross-feed dial graduated in hundredths of mm marked with a clip, enables the operator to continue cutting by hand feed for a short distance after the trip dogs disengage the power feed.

Part # 3. Turret:

The turret is a six sided block, carried on the bed of the machine for holding and bringing forward the tools. Each face of the hexagonal turret is provided with four tapped holes to take the screws for holding various attachments, and through the centre of each frame and coaxial with the machine spindle is a hole into which the shanks of the tool may be clamped.

For this clamping a pad bolt is often employed. On the Capstan lathes, the turret is not hexagonal but circular with six holes for accommodating the tools as the tools used for small works need to be held on a flat face.

Since the tools for operating on the job are attached to various turret faces, it is necessary during a cycle of operations to bring each tool into the position for its work. This necessitates indexing and locating the turret to the successive positions in which its faces are square with the spindle axis. On the turret lathe, the turret is supported on a free bearing, so that it may be pulled round easily by hand when clamping arrangement has been released.

It is located in each of the six correct positions by some form of hand operated plunger, and the machine-operator manually indexes it to the required position after releasing the clamp and locating plunger. On the capstan lathe, means are also provided whereby the turret is automatically indexed to the next position when it reaches the extreme end of its withdrawal movement from the previous position.