Lathe Machine – Introduction
A lathe is a machine tool, which holds the workpiece between two rigid and strong supports called centers or in a chuck or faceplate which revolves. The cutting tool is rigidly held and supported in a tool post, which is held against the revolving work. The normal cutting operations are performed with the cutting tool fed either parallel or at right angles to the axis of the work.
Definition Of Lathe Machine:
- A lathe is a machine, which removes the metal from a piece of work to the required shape and size.
- Lathe is one of the most important machine tools in the metal working industry. A lathe operates on the principle of a rotating workpiece and a fixed cutting tool.
- The cutting tool is feed into the workpiece, which rotates about its axis causing the workpiece to be formed to the desired shape.
- Lathe machine is also known as “the mother/father of the entire tool family”.
Function of lathe
Lathe is to remove excess material in the form of chips by rotating the workpiece against a stationary cutting tool
Industrial revolution demanded
- More production
- More Precision
- Changes in Manufacturing process
- Lead to the Development of High speed
- Special purpose lathes
Lathe Machine Diagram :
Types of lathes :
The fundamental principle of operation of all lathes is the same and performs the same function, yet they are classified according to the design, type of drive, the arrangement of gears, and purpose. The following are important types of lathes.
1. Engine or Center lathe:
- It is a general-purpose lathe and is widely used in workshops.
- The main parts of engine lathe are the bed, headstock, tailstock, carriage, lead screw, and feed change gearbox.
- It differs from a speed lathe that it has an additional mechanism for controlling the spindle speed and for supporting and controlling the feed of fixed cutting tool.
- The cutting tool may be fed both in cross and longitudinal direction concerning the lathe axis with the help of a carriage.
- The engine lathe, depending upon the design of the headstock for receiving power, may be classified as belt-driven lathe, motor-driven lathe, and geared head lathe.
- In Belt driven lathe, Power from the motor is transmitted to the spindle by belt drive, In Geared head lathe power from the motor is transmitted to the spindle by the gear drive.
- The speed changes in belt drive are obtained by shifting the belt to different steps of a cone pulley.
- In geared-Head lathe the gear ratio (Spindle speed to motor speed) is changed by Speed- Lever.
- Usage: It is used for producing cylindrical components. By using the attachments and accessories, other operations such as taper turning, Drilling, milling, and grinding may also be performed.
2. Bench Lathe:
The bench lathe is so small that it can be mounted on a bench.
- All the types of operation can be performed on this lathe that may be done on an ordinary speed or engine lathe.
- This is used for small work usually requiring considerable accuracy such as in the production of gauges, punches, and beds for press tools.
3. Tracer Lathe:
A lathe that can follow a template to copy a shape or contour.
4. Automatic Lathe:
- The lathe in which the workpiece is automatically fed and removed without the use of an operator. Cutting operations are automatically controlled by a sequencer of some form.
- The automatic lathes are so designed that the tools are automatically fed to the work and withdrawn after all the operations are completed to finish the work. Since the entire operation is automatic, these lathes require little attention from the operator. These lathes are used for mass production of identical parts.
5. Capstan and turret lathe:
- The lathes which have multiple tools mounted on turret either attached to the tailstock or the cross-slide, which allows for quick changes in tooling and cutting operations.
- The capstan and turret lathes are the modification of engine lathe and is particularly used for mass production of identical parts in a minimum time.
- These lathes are semiautomatic and are fitted with multi-tool holding devices, called capstan and turret heads.
- The advantage of capstan and turret lathe is that several different types of operation can be performed on a workpiece without resetting of the work or tools.
4. Tool room lathe:
- The tool room lathe is similar to an engine lathe and is equipped with all the accessories needed for accurate tool work.
- It has an individually driven-geared headstock with a wide range of spindle speeds. Since this lathe is used for precision work on tools, gauges, dies, jigs, and other small parts, therefore greater skill is needed to operate the lathe.
5. Speed lathe:
- It is driven by power and consists of a bed, a headstock, a tailstock, and an adjustable slide for supporting the tool.
- It has no gearbox, lead Screw, and Carriage. Headstock may have a step-cone pulley arrangement or may be equipped with a Variable Speed Motor.
- Various speeds are obtained by Cone pulley. Since the tool is fed into the work by hand and cuts are very small, therefore this type of lathe is driven at high speeds usually from 1200 to 3600 rpm.
- Usage: It is mainly used for woodworking, centering, metal spinning, polishing, etc.
6. Computer Controlled Lathe:
Highly automated lathes, where cutting, loading, tool changing, and part unloading are automatically controlled by computer coding.
(Computer Numerical Control) is the general term used for a system that controls the functions of a machine tool using coded instructions processed by a computer. Conventionally, an operator decides and adjusts various machine parameters like feed, depth of cut, etc depending on the type of job, and controls the slide movements by hand. In a CNC Machine function and slide, movements are controlled by motors using computer programs. Tools that can be controlled in this manner include Lathes, Mills, and Grinders.
Under CNC Machining, machine tools function through numerical control. A computer program is customized for an object and the machines are programmed with CNC machining language (called G-code) that essentially controls all features like feed rate, coordination, location, and speeds. With CNC machining, the computer can control exact positioning and velocity. CNC machining is used in manufacturing both metal and plastic parts.
- High Repeatability and Precision Aircraft parts
- Volume of production is very high
- Complex contours/surfaces need to be machined.etc
- Flexibility in job change, automatic tool settings, less crap
- More safe, higher productivity, better quality
- Less paperwork, faster prototype production, reduction in lead times
- Costly setup, skilled operators
- Computers, programming knowledge required
- Maintenance is difficult
7. Special purpose lathes:
The works, which cannot be conveniently accommodated or machined on a standard lathe, the special purpose lathes are used. The gap bed lathe which has a removable section in the bed in front of the headstock tom provide a space or gab is used to swing extra large diameter jobs.
a) Crankshaft lathe: is especially used for turning crankshafts.
b) Wheel lathe: is which is of large design, is especially used for finishing the journal and for turning the locomotive driving wheels.
c) Axle lathe: is used for turning car axles.
d) Precision Lathe: The precision turning of previously rough-turned workpieces.
e) Facing Lathe: Used to machine the end faces
f) Vertical lathe: It is used for turning and boring very large and heavy rotating parts that cannot be supported on other types of lathes.
Classification of lathes / Types Of Lathe Machine
Lathes are very versatile of wide use and are classified according to several aspects:
According to configuration:
- Horizontal – Most common for ergonomic conveniences.
- Vertical – Occupies less floor space, only some large lathes are of this type.
According to the purpose of use:
- General-purpose – Very versatile where almost all possible types of operations are carried out on wide ranges of size, shape, and materials of jobs; e.g.: center lathes.
- Single-purpose – Only one (occasionally two) type of operation is done on limited ranges of size and material of jobs; e.g.: facing lathe, roll turning lathe, etc.
- Special purpose – Where a definite number and type of operations are done repeatedly over a long time on a specific type of blank; e.g.: capstan lathe, turret lathe, gear blanking lathe, etc.
According to size or capacity:
- Small (low duty) – In such light duty lathes (up to 1.1 kW), only small and medium-size jobs of generally soft and easily machinable materials are machined.
- Medium (medium duty) – These lathes of power nearly up to 11 kW are most versatile and commonly used.
- Large (heavy-duty)
- Mini or micro lathe – These are tiny table-top lathes used for extremely small size jobs and precision work; e.g.: Swiss-type automatic lathe.
According to the configuration of the jobs being handled:
- Bar type – Slender rod-like jobs being held in collets.
- Chucking type – Disc type jobs being held in chucks.
- Housing type – Odd shape jobs, being held in the faceplate.
According to precision:
- Precision (lathes) – These sophisticated lathes meant for high accuracy and finish and are relatively more expensive.
According to the number of spindles:
- Single spindle – Common.
- Multi-spindle (2, 4, 6, or 8 spindles) – Such uncommon lathes are suitably used for fast and mass production of small size and simple shaped jobs.
According to the type of automation:
- Fixed automation – Conventional; e.g.: single spindle automat & Swiss-type automatic lathe
- Flexible automation – Modern; e.g.: CNC lathe, turning center, etc.
Lathe Machine Parts :
The bed is a heavy, rugged casting and it carries the headstock and tailstock for supporting the workpiece and provides a base for the movement of the carriage assembly, which carries the tool.
The headstock is provided on the left-hand side of the bed and it serves as housing for the driving pulleys, back gears, headstock spindle, live center, and the feed reverse gear. The headstock spindle is a hollow cylindrical shaft that provides a drive from the motor to work holding devices.
3. Gear Box:
The quick-change gearbox is placed below the headstock and contains several different sized gears.
The carriage is located between the headstock and tailstock and serves the purpose of supporting, guiding, and feeding the tool against the job during operation.
The main parts of carriage are:
a) The saddle is an H-shaped casting mounted on the top of lathe ways. It provides support to the cross-slide, compound rest, and tool post.
b) The cross slide is mounted on the top of the saddle, and it provides a mounted or automatic cross-movement for the cutting tool.
c) The compound rest is fitted on the top of the cross slide and is used to support the tool post and the cutting tool.
d) The tool post is mounted on the compound rest, and it rigidly clamps the cutting tool or tool holder at the proper height relative to the work centerline.
e) The apron is fastened to the saddle and it houses the gears, clutches, and levers required to move the carriage or cross slide. The engagement of split nut lever and the automatic feed lever at the same time is prevented she carriage along the lathe bed.
The tailstock is a movable casting located opposite the headstock on the ways of the bed. The tailstock can slide along the bed to accommodate different lengths of the workpiece between the centers. A tailstock clamp is provided to lock the tailstock at any desired position.
6. Lead screw:
A lead screw also known as a power screw is a screw, moves the carriage by a precise increment for every rotation of the screw. The lead screw is made with square, acme, or buttress type threads.
- Distance between centers
- Swing over the bed
- Swing over the cross slide
- Horsepower of the motor
- Number of speeds
- Feed Given
Lathe Machine Operation :
The machining operations generally carried out in center lathes are :
• Rough and finish turning
• Chamfering, shouldering, grooving, recessing, etc
• Axial drilling and reaming by holding the cutting tool in the tailstock barrel
• Taper turning by
⎯ offsetting the tailstock
⎯ swiveling the compound slide
⎯ using form tool with taper over the short length
⎯ using taper turning attachment if available
⎯ combining longitudinal feed and crossfeed, if feasible.
• Boring (internal turning); straight and taper
• Forming; external and internal
• Cutting helical threads; external and internal
• Parting off
In addition to the aforesaid regular machining operations, some more operations are also occasionally done, if desired, in center lathes by mounting suitable attachments available in the market, such as,
• Grinding, both external and internal by mounting a grinding attachment on the saddle
• Copying (profiles) by using hydraulic copying attachment
• Machining long and large threads for leadscrews, power-screws, worms, etc. by using thread milling attachment.
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