Types of lathes
Lathes are available in large variety of types and sizes. It is difficult to classify them into categories. There is a fairly large variation in their design, construction and use. However, according to their construction and design we can classify the lathes as follows:
1. Bench Lathe:
It is a very small lathe and is mounted on a separately prepared bench or cabinet. It is used for small and precision work since it is very accurate. It is usually provided with all the attachments, which a larger lathe carries, and is capable of performing almost all the operations which a larger lathe can do.
2. Speed Lathes:
These lathes may be of bench type or they may have the supporting legs cast and fitted to the bed. These lathes have most of the attachments which the other types of lathe carry but have no provision for power feed. They have no gear box, carriage and the lead screw. With the result, the tool is fed and actuated by hand. Usually the tool is either mounted on a tool post or supported on a T-shaped support. Such lathes are usually employed for wood turning, polishing, centring and metal spinning, etc. Thus, they can be considered as merely of a theoretical value so far as the modern machine shops are concerned. They are named so because of the very high speed at which the spindle rotates.
3. Engine Lathe:
It is probably the most widely used type of lathe. The name Engine Lathe is a little confusing in modern practice as all these lathes are now made to have an individual motor drive. However, it carries a great historical significance that in the very early days of its development it was driven by a steam engine. From this, it derived the name which is popular even today.
Although it practically resembles a speed lathe in most of its features, but its construction is relatively more robust. Its headstock is bigger in size and more robust, incorporating suitable mechanism for providing multiple speeds to the lathe spindle. The headstock spindle may receive power, from a lathe shaft or an individual motor, through belts. In that case, it will have a cone pulley with back gears in the headstock to provide different speeds to the spindle. It carries a combination of gears, instead of the cone pulley and back gears combination, the lathe is known as geared head lathe and the headstock as all geared head stock.
4. Tool Room Lathe:
It is nothing but the same engine lathe but equipped with some extra attachments to make it suitable for a relatively more accurate angle of speeds and feeds. The usual attachments provided on a tool room lathe are taper turning attachment, follower rest, collets, chucks, etc. This lathe is made to have a comparatively smaller bed length than the usual engine lathe. The most commonly used lengths are 135 to 180 cm.
5. Capstan and Turret Lathe:
These lathes form as very important and useful group and are vastly used in mass production. These machines are actually of semi-automatic type and a very wide range of operations can be performed on them. In operating these machines, a very wide range of operations can be performed on them. In operating these machines, a very little skill is required of the operator. Whatever skill is needed of the operator is only in the setting of tools in the turret or capstan head, and once this setting has been successfully accomplished further operation of these machines is more or less automatic. They carry special mechanisms for indexing of their tool heads.
6. Automatic Lathe:
These lathes help a long way in enhancing the quality as well as the quantity of production. They are so designed that all the working and job handling movements of the complete manufacturing process for a job are done automatically. No participation of the operator is required during the operation. Another variety of this type of lathes includes the semi-automatic lathes, in which the mounting and removal of work is done by operator whereas all the operations are performed by the machine automatically. Automatic lathes are available having single or multi spindles. They fall in the category of heavy duty, high speed lathes mainly employed in mass production.
7. Special Purpose Lathes:
A large number of lathes are designed to suit a definite class of work and to perform certain specified operations only. They prove to be more efficient and effective as compared to the common engine lathe so far as this specified class of work is concerned. A brief description of these machines will be given in the following table.
|Name of Machine||Special Description||Application|
|Precision Lathe||Capable of giving a dimensional accuracy of 0.002 mm.||Precision turning of previously rough-turned workpiece.In many cases, replace a high class grinding machine because of its fine dimensional accuracy.|
|Facing Lathe||In this, the carriage is driven by a separate motor, independent of the main spindle. It carries no tailstock||Used to machine the end faces of bulky cylindrical jobs.|
|Frontal Lathe||In this, two carriages are provided, one on each end. Also, two tool heads are provided. This enables machining of two jobs simultaneously||Its specific use is in machining short jobs|
|Vertical Lathe||It carries a vertical column, on which are fitted the cross slide and vertical slide. A heavy base at the bottom carries a face plate to hold the jobs.||It is used for turning and boring very large and heavy rotating parts which cannot be otherwise supported on other types of lathes. These machines are specifically employed for jobs like heavy flywheels and large gear blanks etc.|
|Crankshaft Lathe||It carries all the attachments, like taper turning and threading, etc. In addition, a number of rests (supports) for the shafts.||It is used for turning very long parts such as turbine and engine shafts and crankshafts.|
|Production Lathe||It distinguishes itself by its bed which is made inclined towards the rear for ensuring an efficient chip removal.||Its special design makes it suitable for mass production of cylindrical parts. Its use increases the rate of production of such items. It is not very suitable for repair work.|
|Duplicating Lathe||It carries a special tracer attachment connected to the carriage, which moves along a template and guides the carriage.||It is used for mass production of identical parts where either a previously machined part works as a template or a separate template is prepared and used for this purpose.|
|Screw Cutting Lathe (automatic)||It is operated through cams and cam plates.||It is used for mass production of screwed parts. Especially suitable for precision screw work.|
Table: Applications of Special Purpose Lathes
The classification of lathes cannot be confined merely to the broad outlines given above. They can be further classified according to the type of drive they possess and their sizes, etc. According to the height of centres (Above the bed) lathes can be grouped as:
- – Small Lathes: Having height of centres up to 150 mm.
- – Medium Size Lathes: Having height of centres from 150 to 300 mm.
- – Heavy Duty Lathes: Having height of centres above 300 mm.
According to the type of drive, the lathes can be grouped as:
- Having step-cone pulley drive and the back-gears to provide various speeds to the work. This type of drive calls for the use of a countershaft which carries a similar cone pulley to that provided on the lathe spindle. This countershaft, in addition to the step pulley, carries two clutch pulleys also, which are connected to the main shaft through belts. One of these pulleys carries an open belt and the other a cross belt. With this arrangement of belts the machine spindle can be rotated in opposite directions according to the requirement by making use of any one of these belts at one time. With suitable combination and selection of different steps on cone pulleys and the engagement or disengagement of back gears, a fairly wide range of speeds can be obtained for lathe spindle.
- Lathes having step-cone pulley drive as usual and the back gears, but having individual motor drive, thus eliminating the use of main shaft. In such machines, the countershaft is provided within the machine and it carries a stepped cone pulley. Another pulley is provided at the end of this shaft which is connected usually by ‘V’ belts, to the motor pulley. In this type, the drive is conveyed from the motor to the counter shaft and then to the machine spindle. Here again the same range of speeds can be obtained with suitable combination as described above.
- Lathes having single pulley constant speed or geared-head drive. In this, a single pulley is driven by means of ‘V’ belts by the motor and then the internal mechanism of the head stock, which is designed to have various speed gears inside, enables a wide range of speeds of the spindle. The quick-change gears provide power feed to the carriage. Although, these machines can be made to receive power from main shaft through the countershaft, but the individual motor drive is the prevailing practice in modern times.
Taken from “A Course in Workshop Technology, Vol II) By B. S. Raghuvanshi