Lathes are powerful tools that find their applications in almost every machining workshop.
These machines are simple to operate but have a complex construction with various parts.
Therefore, in order to understand the functionality of a lathe, it is important to be familiar with its parts and their functions.
This article provides a detailed description of the different parts of a lathe machine.
I've also discussed parts of a CNC lathe and wood lathe to help you understand the differences between each type of lathe.
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Parts of a Metal Lathe
The complex structure of a metal lathe machine consists of various important parts that perform their dedicated functions to successfully execute a machining operation.
The headstock is generally the bulky part of the lathe machine, located on the left of the bed.
It is the powerhouse of the lathe and houses various drive components such as spindle motor, gearbox, belt drive, and work holding devices.
Apart from that, it also houses the speed/feed control levers and other important control switches.
The headstock has an all-metal structure, generally cast-iron, that provides strength and rigidity to resist strong vibrations produced during the operation of the machine.
It is a stationary component of a lathe that has no relative motion with respect to the lathe bed.
Generally, CNC lathes provide an upgrade option where a bar feeder is connected to the headstock of the lathe to automate the feeding of the raw material for continuous operation.
Lathe machines are versatile tools that can be used for machining various different materials.
This versatility is achieved by the ability to provide variable spindle speeds to match the optimal parameters for different machining processes.
Lathe speed variation can be achieved by various methods, such as varying the speed of the motor by varying the electric voltage, by using a belt and pulley mechanism, or by using a gear drive system.
The gearbox of a lathe is similar to a gearbox used in an automobile to vary its driving speed.
It consists of different gear combinations that can provide low-speed/high torque or high-speed/low torque configurations, depending on the machining application.
The gearbox transmits the rotary movement from the electric motor to the lathe spindle.
The lathe spindle is the rotary component of the lathe that provides the necessary motion to the workpiece.
The rotary motion of the electric motor is transmitted to the spindle through a suitable gear mechanism, which thereby rotates the chuck and workpiece.
It is located inside the headstock and consists of a spindle shaft, which can be characterized by its varying cross-section geometry and has threads cut on its leading end.
These threads serve the purpose of fastening to mount the work holding devices, such as chuck or collet.
A typical lathe consists of one spindle to rotate the workpiece, but you can also find lathes with multi-spindle configurations which enhance their productivity.
Chuck is a work holding device used for mounting workpieces of different diameters.
Three-jaw chucks generally have an automatic adjustment, whereas four-jaw chucks can have a manual adjustment, in which each jaw is to be individually loosened or tightened with the help of the chuck key.
This adjustment of the jaws helps align the workpiece to ensure eccentricity with the spindle axis.
It must be noted that a slight offset in the axis can result in improper machining output, and therefore it is important to use aligning instruments such as dial indicators, to minimize workpiece offset.
The bed is the longest component of a lathe machine that usually has a cast-iron structure.
It provides the lathe with a rigid structure and houses all the major components such as spindle, toolpost, gantry, tailstock, etc.
Generally, the length of the bed determines the maximum length of the workpiece that can be machined on the lathe, and the larger the bed size the higher will be the cost of the lathe.
A chip pan is a metallic tray located at the bottom of the lathe.
It collects the chips produced during the machining process, thereby eliminating the need for collecting the chips from the shop floor.
Guideways are metallic rails with an inverted V structure and are present on the bed of the lathe.
As the name suggests, they guide the Z-axis movement of the carriage and the tool post.
A carriage is a movable part of a lathe machine that houses other parts such as a tool post, apron, saddle, cross-slide, etc.
It is configured with the feed rod of the lathe and consists of a hand wheel to control its movement along the length of the lathe (Z-axis).
Therefore, the speed of the carriage determines the feed rate during a machining process.
The saddle is a small H-shaped casting element, that functions as a mount to hold the tool post.
It is located on top of the carriage of the lathe.
Cross-slide is located on the saddle and is responsible for providing lateral movement (along X-axis) to the cutting tool.
This movement of the cutting tool determines the depth of cut during the machining process.
The compound slide is mounted on the cross-slide with the help of the compound rest.
It provides the ability to set the cutting tool at an angle with the workpiece. This enables to perform angled cutting operations, such as chamfering, tapering, etc.
Unlike carriage and cross-slide, a compound slide cannot be positioned with the help of handwheels and, therefore, should be set at the desired angle before executing the process.
Toolpost, as the name suggests, houses the cutting tool used for lathe operation.
It is mounted on the cross-slide and can be moved longitudinally (along Z-axis) or laterally (along X-axis), and the combined X and Z movement of the tool post results in the desired machining operation.
The tool posts used on metal lathes can have four configurations: Single screw, Open side, Four bolt, and Four-way toolpost.
Single screw and open side tool posts can hold a single cutting tool. However, the open side tool post is capable of delivering comparatively stronger cutting forces.
A four-bolt tool post can hold two cutting tools and is ideal for delivering strong cutting forces.
Whereas a four-way toolpost can hold four cutting tools, with each tool clamped by two bolts, making it ideal for heavy machining applications.
Apart from this, certain lathes, such as gang tool lathes, can have special tool posts that can hold multiple cutting tools for different lathe operations.
An apron is an important element that provides the ability to set automatic feed during a machining operation.
It is located on the carriage of the lathe and is coupled with the feed rod to facilitate its automatic movement.
A lead screw is a long driveshaft with acme threads cut on it.
It facilitates longitudinal movement of the carriage, similar to a feed rod, but is used to set automatic feed of the cutting tool.
This automatic feed setting is generally used for thread cutting and finish turning operations, where uniform and precise feed of the cutting tool is required.
Handwheels are used to position various elements of a lathe machine. Each element has a dedicated hand wheel which can be rotated to set its precise position for machining operation.
Typical lathe machines consist of three hand wheels, each controlling the movement of the carriage, tailstock, and cutting tool.
Machining metal workpieces requires strong cutting forces, which generate high frictional heat, and therefore, metal lathes require a coolant system to prevent tool or workpiece damage.
The coolant system consists of a storage tank containing the cutting fluid, a pump to deliver the cutting fluid to the machining area, and a delivery hose placed right above the cutting area.
This cutting fluid serves the purpose of lubrication and acts as a cooling medium by taking away the heat from the point of contact.
The tailstock is another important part of a lathe machine that is situated at the right end of the lathe bed.
It provides support to the leading end of the rotating workpiece during the machining process.
Similar to the carriage, it can slide along the guideways and lock at the desired position.
This movement along the lathe bed enables the tailstock to support workpieces of variable lengths.
Apart from that, tailstock can also be used to mount cutting tools for operations like drilling, boring, reaming, etc.
It generally has a hexagonal structure and can hold six cutting tools. The turret can be rotated to access different cutting tools during a machining process, thereby enhancing the productivity of the lathe.
Turrets can also be found in CNC lathes such as swiss lathes, where multiple cutting tools are required for a machining process.
The legs of a lathe generally have a cast-iron build that provides them with strength and rigidity to carry the entire weight of the lathe.
It is recommended to secure the legs of the lathe with the shop floor, by embedding them in the foundation or using fasteners such as bolts.
This helps to minimize vibrations and enhance the machining quality of the lathe.
However, benchtop lathes do not have legs and are mounted on top of a bench.
Parts of a CNC Lathe
The construction of a CNC lathe is similar to manual metal lathes, with certain modifications that enhance its performance and provides the ability to automate the machining process.
CNC lathes generally consist of a servo motor, instead of a DC motor, to drive the spindle.
Servo motors provide better speed control and are automation ready.
These motors work on a closed loop system, where they can detect and rectify an error in the operation of the motor without the need for human interference, making it ideal for CNC lathe machines.
However, servo motors are costly when compared to other motors used in CNC machines.
The primary motive of CNC lathes is to provide quick machining operation with high accuracy and efficiency.
Hydraulic chucks, when compared to manual jaw chucks, are easy to align as they can clamp the workpiece automatically by the action of hydraulic fluid.
Generally, 3-jaw hydraulic chucks with internal diameter (ID) and outer diameter (OD) jaw configurations are used in CNC lathes.
The tool turret of a CNC lathe holds multiple cutting tools that are used during the machining operation.
Each tool position in the turret is numbered and can be indexed automatically according to the machining program.
Tool turrets are available in different shapes and sizes depending upon the number of tools that it can hold.
Machine Control Unit (MCU)
CNC lathes consist of a control unit that takes in the G-code from the computer and translates them into electric signals to control various elements of the lathe.
The machine control unit of a lathe consists of the controller, input switches, and a screen to set and monitor the machining parameters.
MCU of lathes works with specific CNC control software such as FANUC, Hass, Siemens, Hydro-Dyne, and Mitsubishi.
Foot pedals or foot controls on a CNC lathe enable a CNC operator to control certain features with their feet.
Generally, the left pedal controls the clamping and de-clamping of the work holding device and the right pedal controls the tailstock.
Parts of a Wood Lathe
Wood lathes are generally smaller in size but have a similar construction to metal lathes, with the only difference being the tool post of the lathe.
The cutting tool used in wood lathes is a hand-held tool that can be moved around freely by the operator to carve the desired shape from the wooden stock.
This eliminates the need for various elements, such as tool post, carriage, feed rod, etc., that holds the cutting tool and facilitate moving the tool along different lathe axes.
However, wood lathes consist of a tool rest that is used to support the cutting tool during the machining operation.
The tool rest consists of various elements such as banjo, banjo lock, and tool rest lock, that help in the accurate positioning of the cutting tool for effective machining of wood.
Banjo is the base of the tool rest. It consists of an O-shaped clamp nut that slides into the guideway and facilitates its movement along the lathe bed.
A banjo lock is a lever that is used to lock the Banjo in its position.
After sliding the banjo to the desired location along the guideways, you can engage the banjo lock to hold the tool rest securely for machining operation.
Tool rest Lock
The tool rest of a wood lathe generally has a flat geometry to place the cutting tool perpendicular to the workpiece.
However, to place the cutting tool at an angle, you can disengage the tool rest lock, set the desired orientation of the tool rest, and then engage the tool rest lock again to secure it in that position.
Workpiece Mounting Device
Wood lathes generally use a spindle spur or faceplate for mounting the workpiece.
A spindle spur is an extension of the spindle shaft, with a sharp profile that digs into the workpiece and holds it firmly between the headstock and the tailstock.
Faceplate is a metallic plate that holds a wooden workpiece with the help of fasteners such as screws.
Apart from this, wood lathes can also consist of jawed chucks or collets for mounting the workpiece.
Frequently Asked Questions (FAQ)
What does "swing over bed" mean in lathes?
The swing over bed (SOB) of a lathe means the maximum workpiece diameter that can be machined on that lathe. It is generally equal to twice the distance between the top of the bed and the center of the spindle.
What is "distance between centers"?
Distance between centers (DBC) is the distance between the tailstock and the headstock of the lathe. It is generally equal to the length of the bed and determines the maximum length of the workpiece that can be turned on the lathe.
Can you use a CNC lathe to machine wood?
Yes, a CNC lathe provides variable speed control and can therefore be adjusted to machine wood. However, each wooden stock differs from the other in terms of its fiber orientation, grain structure, etc., and a hand-held tool provides vibrational feedback to help the machinist adapt the process accordingly. This cannot be achieved in CNC lathes, and therefore CNC lathes can be used for machining of wood, but at the cost of its surface finish.