There are two principal types of turret lathes: 1. The Ram Type 2. The Saddle Type.
Some of them are given below:
Regarding the kind of blank or stock to be processed, turret lathes are divided into bar and chucking machines. As to size, turret lathes are classified as small (bar capacity d = 25 mm, chucking capacity D = 320 mm), medium (d = 80 mm, D = 500 mm) and large (d = 160 mm, D = 800 mm). According to the turret arrangement, turret lathes are classified as those having turrets with a horizontal (Fig. 32.2 a), vertical (Fig. 32.2 b), and inclined (Fig. 32.2 c) axis of rotation.
Turret lathes with vertical-axis and inclined-axis turrets are furnished with cross slides in addition to turret slides, whereas those with a horizontal-axis turret have no cross slide since the cross feed of the tool is effected by the turret slide itself.
Headstock 1 of the turret lathe (see Fig. 32.2) contains mechanisms that serve to clamp the work and rotate it at the required speed. Cutting tools are held by the turret or by the tool holder on cross slide 4, which imparts feed motions to the tool.
The headstock, the turret slide, and the cross slide are mounted on bed 2, on which all principal and auxiliary motions take place during machining.
1. Ram Type:
In the ram type of turret lathe a slide or ram carrying the turret moves back and forth on a saddle which is clamped to the machine bed. The saddle can be adjusted and clamped to any convenient position along the bed. This type of machine is somewhat lighter in construction and therefore can be quickly and easily operated.
The hexagonal turret has its own ways in the saddle and hence whole saddle need not be moved back and forth when the cutting tools are brought to cutting position and retraced. It is best suited for bars of 6 to 65 mm diameter. This type of lathe is called Capstan Lathe.
2. Saddle Type:
In this type of turret lathe, the hexagonal turret is rigidly mounted on the saddle and the whole unit moves back and forth on the bed ways. An apron on the front of the saddle houses the controls for the turret. This type of machine is heavier, has a long stroke and is more rigid, and hence most suitable for longer and heavier chucking work, requiring heavier and longer cuts. Jobs up to 300 mm diameter can be machined on it.
In addition to it, there are some special purpose machines e.g. bar turret lathe, chucking turret lathe, vertical lathe etc. This further sub classification is according to special features such as method of drive, method of chucking, capacity and number and arrangement of tool slides etc.
Fig. 32.3 shows a schematic of multi-spindle auto. It is preferred for mass productions. Several spindles are incorporated in the headstock, all driven from a central drive shaft. The head is indexed, usually by a Geneva-type mechanism, and machining takes place at all spindles concurrently.
One spindle position is utilized for loading, usually by some form of automatic feed device. Each station is provided with a radially acting tool-holder and provision for a longitudinally acting tool-holder.
It is normal to use complex form tools, and the machine is rigidly constructed and heavily powered to allow for this. To obtain the correct relationship between the movements, these are all actuated from a single main camshaft, either directly or via auxiliary camshafts driven from it.
Such machines are capable of very high output rates, while having relatively short changeover time, since changeover comprises the replacement of a set of cams and the installation of a set of form tools. Initial tooling outlay in the manufacture of cams is relatively high, but these are long lasting and the machines are extremely reliable. For large quantity second operation work, such machines are ideally suited.
Multi-spindle Autos may also be bar-fed, with one station of the turret taken up by a feed-to-stop operation, and with one utilized for part-off. If the cutting time at the other stations is long, both the part-off and the feed may be carried out at the same station.