A lathe machine is a machine tool used primarily for shaping, cutting, drilling, knurling, sanding, facing, or turning materials, typically metal, wood, or plastic by rotating the workpiece against a stationary cutting tool. It is widely regarded as the “mother of all machine tools” due to its fundamental role in shaping materials into symmetrical forms. Lathe is a machine tool commonly used in all industrial applications. Now, a machine tool is power-driven and designed to move a sharp cutting tool against a rigidly held workpiece material or vice versa to remove material from the workpiece. The Mechanical Engineering stream has seen some tremendous machines invented and modified all these years. One of the remarkable machines that completely revolutionized the way we perform operations on metal or wood is the Lathe Machine.

In this article, we will discuss the definition, parts, working principle, and types of lathe machines. You will learn the operations that are performed on the machine in brief. This article helps you to understand the concepts of this oldest machine helping you with SSC JE ME, GATE ME, and RRB JE Mechanical engineering exams.

What is a Lathe Machine?

A lathe machine is a machine tool that is used to remove unwanted material from a rotating workpiece in the form of chips. This is accomplished with the use of a tool that traverses across the workpiece and feeds into it. The machine is used to accomplish all fundamental operations, including drilling, sawing, tapping, and turning, among others, with the aid of various tools located in the work area. Hence, the lathe is also referred to as the “Mother of all machines.”

Andrei Nartov, a Russian engineer, created one of the earliest lathes in 1718. It featured a carriage for holding mechanical cutting tools and a system of gears. In the 1950s, servomechanisms were applied to the numerical control of lathes and other machine tools, which were frequently linked with computers to produce computerised numerical control (CNC). Both manually driven and computer numerical control, or CNC, lathes are used in the industry today. 

Fig 1: Oldest Lathe Machine

You may be wondering about the various parts of this ancient machine tool. This section helps you learn all the parts that are responsible for the work done on the machine. Refer to the lathe machine diagram below as you learn.

Fig 2: Lathe Machine Parts

Bed

The bed of the lathe machine serves as the foundation upon which all other components are installed. The bed is supported by large box-section columns and is made of cast iron or a nickel cast iron alloy. The bed itself is mounted on the legs which are bolted to the ground.

Headstock

The headstock is mounted on the left side of the lathe bed. Its primary duty is to transmit electricity to the components. It is a housing for a spindle where a chuck or live centre is provided that holds one end of the workpiece as it rotates. Also, it contains a necessary transmission system with levers for changing speeds.

• Lathe Chuck: Chucks are specialised clamps made to hold objects having radial symmetry such as cylinders. They typically have jaws to secure the workpiece. The jaws (or dogs) are organised in a star-like configuration with radial symmetry.
• Lathe Spindle: An essential rotating part of a headstock is the spindle. It contains a shaft that transfers rotary motion to the chuck, thereby turning the workpiece. It is supported by two sets of angular contact ball bearings to help handle both radial and axial loads.

Tailstock

The tailstock is a moveable casting opposite to the headstock that is mounted on the guideways on the bed. It holds tools for operations like drilling, reaming, tapping, etc., and supports the opposite end of the workpiece during machining. It includes the dead centre, adjustment screws, and handwheel.

• Dead Centre: The workpiece is held in place while it is rotating using a dead centre (not freely rotated, i.e., dead). There may be friction on the dead centre due to the rotation of the workpiece when employed in the stationary position. The pointed end of it is placed touching the other end of the workpiece to avoid an abrupt stop in rotation and reduce friction.

Carriage

The carriage can be found in the area between the tailstock and headstock. During operation, the carriage serves as a guide, supports, and feeds the tool against the workpiece. The following parts are on the carriage.

• Saddle: It is cast in the shape of an H and installed on top of the lathe. It supports the cross-slide, the compound rest, and the tool post. Manual or automatic feeding is employed to move the saddle.
• Cross Slide: It is positioned on the saddle such that it is perpendicular to the bed. One side of the cross slide is equipped with a female dovetail, and it is joined on top of the saddle using its male dovetail. The cross slide hand wheel is turned to move the cross slide at a right angle to the axis of the lathe.

Compound Rest

The compound rest joins the cross slide with the compound slide using a tongue-and-groove joint. It supports the cutting tool and tool post during the drilling of short tapers and shapes on forming tools.

• Tool Post: The tool post is mounted on the compound rest and is used to carry cutting tool holders. The holders are supported by a wedge with a bottom that fits into a ring with a concave surface. It is attached to the upper slide. The tool post is positioned on the top of the compound slide to securely hold the tools. 
• Apron: An apron is the front section of a carriage. It includes all control keys. The apron is made up of split nuts that engage with the lead screw when cutting threads, as well as gears and clutches for transferring motion from the feed rod to the carriage.

Leadscrew

A leadscrew is used as a linkage in a machine to convert turning motion into linear motion. It is also referred to as a power screw or translation screw. The lead screw in a lathe machine is used to move the carriage along with the revolution of the spindle. Using various gears between the lead screw drive and spindle, threads can be created.

Working Principle of Lathe Machine

With the knowledge of the components of the lathe machine, we will be able to understand the working principle of lathe machine. This remains common to all types of lathes with some minor changes.

Fig 3: Working Principle of Lathe Machine

The working principle of lathe machine involves rotating a workpiece against a fixed cutting tool. As seen in the figure above, the chuck (live centre) and the tailstock (dead centre) hold the workpiece to be machined. The tool is moved horizontally or vertically along the surface of the workpiece to create circumferential (cylindrical) or deep cuts respectively. The tool is moved in an inclined plane along the vertical to produce tapered surfaces on the workpiece. Apart from this, normal cutting operations are performed on the lathe as the workpiece is firmly fixed between the centres.

Lathe Machine Operations

We just discussed that lathes can aid in various operations which include drilling, reaming, boring, etc. Let us study all the operations that can be performed on a lathe in this section referring to the function of lathe machine.

Turning

The process of reducing the external diameter of a cylindrical workpiece using a single-point cutting tool, as shown in the animation below, is called turning. The process has types such as taper turning, straight turning, profiling, and external grooving.

Turning Operation 

Facing

The process of reducing the overall length of the workpiece and producing a flat surface as a result is called facing operation. We can use a normal turning tool for this operation as shown in the animation below.

Facing Operation

Drilling

The process of creating a cylindrical hole in a workpiece by rotating the cutting edge of a drill is called Drilling. The tool used is called a drill bit which is mounted to the tailstock or dead centre instead of the tool post as shown in the image below.

Fig 4: Drilling Operation

Boring

The boring operation on lathe machine involves enlarging a hole previously drilled, sometimes to create circular interior grooves. Holes can be drilled straight (Counter-boring) or tapered (Taper-boring). In this process also, the boring tool is attached to the tailstock.

Fig 5: Boring Operation

Reaming

The process of sizing and completing a hole that has already been drilled or bored is called reaming. A tool with several cutting edges called a ‘reamer’ is used specifically for this operation. An image of this operation is shown below.

Fig 6: Reaming Operation

Knurling

The process of knurling involves embossing a pattern, usually diamond-shaped, on the surface of the workpiece mounted on the lathe machine as shown in the image below. The knurling process is usually done to provide the workpiece with a good gripping surface.

Knurling Operation

Chamfering

The process of creating a symmetrically sloping edge or corner on an object is called chamfering, also known as the ‘bevelling’ procedure. The purpose of the chamfer is to protect the end of the workpiece from damage by removing burrs from uneven surfaces to create an even surface.

Fig 7: Chamfering Operation

Parting

A machining process that produces a cut-off portion from the workpiece at the end of the machining cycle is called parting. While the workpiece rotates, a tool with a certain shape penetrates the workpiece in a direction that is perpendicular to the rotating axis. ‘Parting-off tool’ is used for this process.

Fig 8: Parting Operation 

Thread Cutting

The operation of creating a helical groove on a conical or cylindrical surface of the workpiece by feeding the tool longitudinally is called threading or thread cutting operation. The desired thread type is obtained by longitudinally moving the tool.

The left-hand thread is obtained when the tool is moved from the right to the left and vice versa. Thus, the lead screw is responsible for the motion of the carriage. It also allows adjusting the depth of the cut.

Thread Cutting Operation

Grooving

The grooving operation involves reducing the external diameter workpiece to a relatively small surface area. It is done to leave a thin margin at the end of a thread or close to a shoulder. The grooving usually consists of three types: Square, Round, and Bevelled.

Grooving Operation 

Forming

The process of turning concave, convex, or other asymmetrical shapes is called forming operation. This can be done in several ways:

• Using a dedicated forming tool
• Tracing a template onto the workpiece.

In general, straight and circular shaping tools are utilised. The straight type is used for wider surfaces while the circular form is utilised for narrow surfaces.

Fig 9: Forming Operation

Polishing

It is usually done as a final process. The operation involves smoothening the external or internal surface of the workpiece after all necessary machining operations. A sandpaper or emery cloth is used for this process while the lathe machine runs at higher speeds ranging from 1500 to 1800 RPM.

An animation is shown below of an operator polishing the workpiece.

Types of Lathe Machines

Now, we have understood the lathe machine operations. Let us feed our curious minds with the types of lathe machines available.

Specification of Lathe Machine 

We understood the types of lathe but in industries, the machines are specified based on certain criteria. Below are some of the specifications of lathe machines that are commonly used in the manufacturing industries. These play a major role in buying decisions the industries make.

• The total distance between the two centres
• Total height from the bottom to the centre
• Radius of the swing of tool post
• Horsepower of motor or the maximum rpm
• Overall dimension of the lathe like “length x width x height” including the total weight. This is considered for shipping especially.
• Maximum travel distance of the tailstock sleeve
• Pitch of leadscrew.

Advantages of Lathe Machine

A machine to leaves a legacy and remain used throughout history should have some remarkable advantages. Below are some of the notable advantages of using a lathe.

1. The final quality of a lathe machine is always high and acceptable, especially while working with CNCs.
2. All the operations discussed above can be done at high speeds
3. Due to this, a lot of time is saved from switching between various dedicated machines for a small job.
4. As most lathes are affordable, there is a reduction in initial investment compared to profit.
5. The biggest advantage is the ability to cut threads with ease on the machine.

Disadvantages of Lathe Machine

As the advancements in technology made so many improvements to these ancient machines, the disadvantages of these machines became evident. Some of them are discussed below.

1. There should be constant maintenance of these machines like lubrication, cleaning, and checking the fasteners.
2. Obviously, this demands skilled labourers to operate.
3. CNC machines need operators who know to program the operations. This infers a demand for training.
4. Shape and structure are limited, and hence the weight of the machines remains almost the same.

Application of Lathe Machine

The application of a lathe machine is generally dependent on the type of machine. However, some common applications are listed below.

• Kitchenware like huge utensils and pressure cookers
• Woodworking industry
• Almost every manufacturing industry that deals with cylindrical metal parts
• Metal restoration industries
• Precision part manufacturing like customised cutting tools.

Though the machine is old, the concept is still fresh for you to crack the GATE ME exam. It is also essential to crack the AE/JE Mechanical exams. As we remembered the old memory of the lathe, you also do that same using the SSC JE ME test series along with the GATE ME test series. 

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