Lathe Machine
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Lathe machine is one of the most versatile and widely used machine tools all over the world. It is commonly known as the mother of all other machine tool. The main function of a lathe is to remove metal from a job to give it the required shape and size. The job is securely and rigidly held in the chuck or in between centers on the lathe machine and then turn it against a single point cutting tool which will remove metal from the job in the form of chips. An engine lathe is the most basic and simplest form of the lathe. It derives its name from the early lathes, which obtained their power from engines. Besides the simple turning operation as described above, lathe can be used to carry out other operations also, such as drilling, reaming, boring, taper turning, knurling, screw thread cutting, grinding etc.
TYPES OF LATHE
1 Speed Lathe
Speed lathe is simplest of all types of lathes in construction and operation. The important parts of speed lathe are following-
(1) Bed
(2) Headstock
(3) Tailstock, and
(4) Tool post mounted on an adjustable slide.
It has no feed box, lead screw or conventional type of carriage. The tool is mounted on the adjustable slide and is fed into the work by hand control. The speed lathe finds applications where cutting force is least such as in wood working, spinning, centering, polishing, winding, buffing etc. This lathe has been so named because of the very high speed of the head stock spindle.
2 Center Lathe or Engine Lathe
The term “engine” is associated with this lathe due to the fact that in the very early days of its development it was driven by steam engine. This lathe is the important member of the lathe family and is the most widely used. Similar to the speed lathe, the engine lathe has all the basic parts, e.g., bed, headstock, and taistock. But its headstock is much more robust in construction and contains additional mechanism for driving the lathe spindle at multiple speeds. An engine lathe is shown in below Fig. Unlike the speed lathe, the engine lathe can feed the cutting tool both in cross and longitudinal direction with reference to the lathe axis with the help of a carriage, feed rod and lead screw. Center lathes or engine lathes are classified according to methods of transmitting power to the machine. The power may be transmitted by means of belt, electric motor or through gears.
3 Bench Lathe
This is a small lathe usually mounted on a bench. It has practically all the parts of an engine lathe or speed lathe and it performs almost all the operations. This is used for small and precision work.
4 Tool Room Lathe
This lathe has features similar to an engine lathe but it is much more accurately built. It has a wide range of spindle speeds ranging from a very low to a quite high speed up to 2500 rpm. This lathe is mainly used for precision work on tools, dies, gauges and in machining work where accuracy is needed.
5 Capstan and Turret Lathe
The development of these lathes results from the technological advancement of the engine lathe and these are vastly used for mass production work. The distinguishing feature of this type of lathe is that the tailstock of an engine lathe is replaced by a hexagonal turret, on the face of which multiple tools may be fitted and fed into the work in proper sequence. Due to this arrangement, several different types of operations can be done on a job without re-setting of work or tools, and a number of identical parts can be produced in the minimum time.
6 Special Purpose Lathes
These lathes are constructed for special purposes and for jobs, which cannot be accommodated or conveniently machined on a standard lathe. The wheel lathe is made for finishing the journals and turning the tread on railroad car and locomotive wheels. The gap bed lathe, in which a section of the bed adjacent to the headstock is removable, is used to swing extra-large-diameter pieces. The T-lathe is used for machining of rotors for jet engines. The bed of this lathe has T-shape. Duplicating lathe is one for duplicating the shape of a flat or round template on to the job.
7 Automatic Lathes
These lathes are so designed that all the working and job handling movements of the complete manufacturing process for a jobs are done automatically. These are high speed, heavy duty, mass production lathes with complete automatic control.
CENTER LATHE MACHINE
A simple lathe comprises of a bed made of grey cast iron on which headstock, tailstock, carriage and other components of lathe are mounted.
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| Center Lathe or Engine Lathe |
The major parts of lathe machine are given as under:
1. Machine bed
2. Headstock
3. Tailstock
4. Carriage
1. Machine bed
Machine bed, usually made of cast iron. It holds or supports all other parts of the lathe. The top of the machine bed is flat and is machined to form guide ways on which the carriage slides along the length of the lathe.
2. Headstock
It is fixed at the extreme left hand of the bed and contains shafts and gears immersed in lubricating oil. The driving shaft inside is driven by an electric motor. The driven shaft, which is in the form of a hollow spindle can be driven at various r.p.m. by changing gears, projects out of the headstock, A chuck (either three jaw or four jaw), is screwed on this spindle. The work piece can be held in the jaws of the chuck. When the spindle rotates, the chuck as well as the work piece held also rotate about the longitudinal axis of the spindle.
3. Tailstock
A tailstock is provided at the right hand end of the bed. It can slide along the guide ways provided on the bed and may be brought nearer to the headstock, if so desired. It can then be clamped or fixed on the bed in that position. The tailstock has a spindle in the upper part of the tailstock, the axis of which coincides with the axis of the headstock spindle, both being at the same height above the bed. This spindle can be moved forwards or backwards by rotating a hand wheel. The front portion of tailstock spindle carries a ‘dead’ or ‘live’ center. When a long work piece is held in the chuck at the headstock end, it is supported at the tailstock end by moving forward the tailstock spindle. Of course, there has to be a small conical hole in the center of the work piece, in which the tailstock center may be inserted to provide support. If the center (being carried in its own bearings) rotates along with the work piece, it is called a live center. However, if the tailstock center remains stationary and work piece alone rotates, the center is called ‘dead centre’ and the conical tip of center has to be lubricated with grease to reduce the friction between the tailstock center and the work piece.
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| Tailstock |
Also Read : types of production system
4. Carriage
A carriage is shown in Fig. The carriage can slide along the length of the machine bed from the tailstock end to the head stock end. This movement is controlled by manually operating the hand traversing wheel. It can also be imparted this traversing motion at different speeds automatically by engaging into the feed rod or feed shaft. The carriage carries a cross slide, which can independently move in a crosswise direction at right angles to the bed. The cross slide can also be moved either manually through a smaller hand wheel or through an automatic device. Mounted upon the cross slide is another small slide, called the compound rest (or tool post slide) which can be rotated in a horizontal plane. Its normal position at 0° rotation is parallel to bed. Its angle of rotation can be read off on a protractor. This compound rest is used during taper turning to set the tool for angular cuts. The compound rest can be moved only manually. The cutting tool is clamped in the tool post which is mounted on top of the compound rest. The gears, clutches and other mechanism required for giving movement to the carriage and cross slide etc. is hidden from view by means of an apron (thin steel plate) screwed upon the front face of the carriage. Half hidden in the front are two long shafts, (the screwed one is called the lead screw shaft/rod and the plain one is called feed shaft/rod) extending from the headstock to the tailstock end. These two shafts can be engaged one at a time to give longitudinal movement to the carriage. Lead screw is only used during the screw cutting operation. Feed shaft is used in other operations like turning. Size of a lathe is specified by the distance between headstock chuck to tailstock center. This is the length of the longest job which can be accommodated or machined on the lathe. In addition the swing of the lathe (i.e., the vertical distance between chuck center and the lathe bed) is specified as this is the radius of the largest work piece which can be turned on the machine.
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| Carriage |
SPECIFICATION OF LATHE
The size of a lathe is generally specified by the following means:
(a) Swing or maximum diameter that can be rotated over the bed ways
(b) Maximum length of the job that can be held between head stock and tail stock centers
(c) Bed length, which may include head stock length also
(d) Maximum diameter of the bar that can pass through spindle or collect chuck of capstan lathe.
The following data also contributes to specify a common lathe machine.
(i) Maximum swing over bed
(ii) Maximum swing over carriage
(iii) Height of centers over bed
(iv) Maximum distance between centers
(v) Length of bed
(vi) Width of bed
(vii) Morse taper of center
(viii) Diameter of hole through spindle
(ix) Face plate diameter
(x) Size of tool post
(xi) Number of spindle speeds
(xii) Lead screw diameter and number of threads per cm.
(xiii) Size of electrical motor
(xiv) Pitch range of metric and inch threads etc.
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