What Is a Lathe?
An Easy-to-Understand Guide to Types and Features
Source: "Hajimete no Kousaku Kikai"
Key Points
- A lathe machines a rotating cylindrical workpiece by pressing a cutting tool against it
- NC lathes equipped with numerical control systems are now the mainstream
- Lathe size is generally expressed by swing and distance between centers
Table of Contents
What Is a Lathe?
A lathe is a machine tool that rotates a cylindrical workpiece mounted on the spindle while moving a cutting tool, called a bite in Japanese, against the workpiece to machine areas such as the outer diameter.
A wide variety of cylindrical parts, including shafts and pins, are produced on lathes.
Machining a rotating workpiece with a cutting tool fixed to the tool post is called turning. Depending on how the tool is moved, various areas can be machined, including the outer diameter, end face, and inner surface of a hole.
Lathes can also perform taper machining for tapered shapes such as cones, tracing operations that copy complex contours, and parting operations that cut off the finished workpiece.
In lathes, a holding device called a chuck is commonly used to mount the workpiece. The workpiece is rotated while clamped by the chuck. This method is widely used for holding relatively short cylindrical workpieces.
When a long, slender workpiece is mounted in a chuck, the unsupported end can deflect when pushed by the cutting tool. To prevent this deflection, the center of the unsupported end face must be supported by a device called a center.
For machining long, slender workpieces, another method is to support both ends of the workpiece with centers instead of using a chuck. However, simply supporting the workpiece does not transmit spindle rotation to it, so devices such as a lathe dog and drive plate are required to transfer the spindle’s rotation.
In the past, engine lathes operated manually by turning handles to control tool movement were widely used on manufacturing floors. Today, however, NC lathes equipped with numerical control systems are the mainstream.
NC stands for “Numerical Control.” An NC lathe can control tool movement and other operations using numerical data, allowing the workpiece to be machined according to a programmed sequence.
The advantages of NC lathes are as follows.
- They can produce workpieces of consistent quality without relying on operator intuition or skill.
- Because all machining steps are programmed, human errors such as misreading drawings or misunderstandings can be prevented.
- Since machining is controlled by NC programs, machining time and procedures remain consistent, resulting in less variation in machining accuracy. This makes quality easier to control and helps reduce defects.
- Even when the workpiece changes, only the program needs to be changed, giving the machine high versatility and flexibility.
- Cutting conditions and other settings can be stored as data, enabling one operator to manage multiple machines.
Tool Wear & Thermal Compensation
- Tool Setter -
Performs wear, chipping, and thermal displacement compensation, contributing to maintaining the constant machining precision of the machine tool
Click here ›Basic Components
A lathe basically consists of the following components: (1) headstock, (2) tool post, (3) carriage, (4) tailstock, (5) bed, and (6) base.
NC lathes also include an NC unit and servo mechanisms that move the spindle and tool post. Aside from the NC unit and servo mechanisms, the basic structure of an engine lathe and an NC lathe is not significantly different.
1. Headstock
This is the section that houses the spindle—the spindle itself is used to mount the workpiece and is one of the most important core components of the lathe. In an engine lathe, the headstock changes spindle speed through gears driven by the motor.
In contrast, NC lathes use servo motors capable of stepless speed control, allowing spindle speed to be freely set through the NC program. In recent years, built-in motors with the motor integrated into the spindle have also become more common.
2. Tool Post and Carriage
The tool post is the part where cutting tools such as turning tools are mounted. The carriage is the base that supports the tool post. Tool posts can be classified by configuration into the “flat type,” which can hold up to four tools at 90-degree intervals, the “gang tool type,” in which tools are arranged in parallel, and the “turret type,” in which tools are arranged radially.
3. Tailstock
The tailstock is positioned opposite the spindle and contains a quill. A center is mounted in the quill. The center is pressed against the end face of the workpiece when stable rotation is required.
4. Bed and Base
The bed serves as the foundation that supports the headstock and carriage. The base is located at both ends of the lathe and supports the machine body. Many lathes have an integrated bed-and-base structure.
The bed and base must have sufficient strength and rigidity to prevent vibration from affecting the machine during machining.
Chip disposal is also an important issue. When a cutting tool machines the workpiece, chips are generated. If chips accumulate, their heat can cause thermal expansion of the bed and base, changing dimensions and potentially reducing machining accuracy. For this reason, chips must be discharged from the machine quickly.
For this reason, slant-bed lathes—with guideways inclined so chips can fall naturally—have become widespread. They make it easier for operators to monitor machining conditions and also reduce the machine’s installation footprint.
By contrast, flat-bed lathes, which have horizontal guideways, are known for their high stability and ease of use. Many are also equipped with chip conveyors to improve chip evacuation.
Automated workpiece centering and positioning
- Touch probe -
A contact/touch sensor for on-machine measurement that improves the efficiency of setup work
Click here ›Lathe Size
Lathes come in a wide range of sizes, from machines for large parts to those for small parts. The standard indicators used to describe lathe size are swing and distance between centers. Swing is further divided into swing over bed and swing over carriage.
Swing refers to the maximum workpiece diameter that can be mounted based on the machine’s structure. Swing over bed indicates the maximum workpiece diameter that can be mounted on the spindle without touching the bed, while swing over carriage means the maximum diameter that can be mounted without interfering with the carriage.
Distance between centers refers to the distance between the center in the spindle and the center in the tailstock when the tailstock is positioned as far as possible from the headstock. In other words, it represents the maximum workpiece length that can be mounted on the lathe.
Swing and distance between centers indicate the maximum workpiece size that can theoretically be machined. However, if a workpiece of the maximum size is mounted, the travel range of the tool post may become insufficient, reducing workability. Therefore, actual workpiece size should be kept within a practical range.
In some cases, bed length is also used as an indicator of lathe size, but as with swing and distance between centers, it should be noted that this may differ considerably from the actual workable part size.
Types of Lathes
1. Gang Tool Lathe
This type of lathe is equipped with a gang tool post in which cutting tools are arranged in parallel like the teeth of a comb. The tool post moves on a plane parallel to the spindle.
Compared with the turret type described later, gang tools generally offer higher positioning accuracy and shorter indexing time. Their simple, linear arrangement of tools also makes them compact and straightforward in design.
On the other hand, they can hold fewer tools than turret lathes, and the narrow spacing between tools can create a risk of interference between unused tools and the workpiece, making complex machining more difficult.
2. Turret Lathe
A turret lathe has a polygonal tool post called a turret. The cutting tools are mounted radially, and the turret rotates to index the tool to be used.
The advantage of the turret is that it provides a larger machining area than a gang tool arrangement. It can also hold more tools than a gang tool lathe, giving it advantages in both machining flexibility and efficiency.
However, the turret tends to be larger and heavier. In addition, because the tools are positioned farther from the center of rotation, positioning accuracy tends to be lower than that of gang tool lathes.
3. Vertical Lathe
A vertical lathe has a spindle oriented perpendicular to the ground. It can be easily imagined as similar to a pottery wheel. The workpiece is placed on a circular table mounted on the spindle and machined there.
Vertical lathes are used for machining workpieces that are difficult to mount on the chuck of a horizontal lathe, such as those with large diameters, heavy weights, or extremely large diameters relative to their length.
4. Automatic Lathe
An automatic lathe is well suited for mass production of workpieces with the same shape.
When combined with an automatic bar feeder that supplies the bar material automatically, it can operate unattended for long periods. It is also called an automatic screw machine.
Automatic lathes are broadly divided into two types: those with a moving spindle and those with a fixed spindle. The moving-spindle type excels in high-volume machining of long, slender workpieces.
Because such workpieces tend to deflect easily, a stabilizing device called a guide bushing is used to suppress runout and deflection. Since this method was developed in Switzerland, it is also known as a Swiss-type automatic lathe.
In the fixed-spindle type, the headstock does not move; instead, the tool post moves in the spindle direction to machine the workpiece. This type is well suited to machining short, thick workpieces.
There are also single-spindle automatic lathes, which repeatedly perform the same process on one spindle, and multi-spindle automatic lathes, which have multiple spindles. In multi-spindle machines, several spindles arranged circumferentially move through different machining stations for turning, drilling, threading, and other operations.
Because machining takes place simultaneously at each station, there is no need to change tools during processing, resulting in extremely high productivity.
5. Engine Lathe
An engine lathe is operated manually using handles and levers attached to various parts of the machine to move the tool post and carriage. It is also called a conventional lathe.
6. Turning Center
A turning center (TC) is a machine tool equipped with rotary tools on the turret or gang tool post of an NC lathe.
Rotary tools are a general term for cutting tools such as milling cutters and end mills that machine the workpiece while rotating. In addition to turning, a turning center can also perform milling operations on a single machine.
7. Advanced Lathes
Some NC lathes have two spindles to improve machining efficiency. Depending on the positional relationship between the spindles, they are classified as parallel twin-spindle lathes or opposed twin-spindle lathes.
In a parallel twin-spindle lathe, the two spindles are arranged in parallel. In an opposed twin-spindle lathe, the two spindles face each other. These machines consolidate the functionality of two separate lathes into a single unit.
Many NC lathes with multiple tool posts are also available on the market. Examples include lathes with two tool posts for one spindle and machines with two spindles and two tool posts. There are even lathes with three tool posts for two spindles, offering very high productivity.
Source: "Hajimete no Kousaku Kikai"
Automated workpiece centering and positioning
- Touch probe -
A contact/touch sensor for on-machine measurement that improves the efficiency of setup work
Click here ›Sensor Implementation Case Studies
CNC automatic lathes, what you ABSOLUTELY need to know for MAXIMUM use?
Those considering the introduction of a CNC lathe may have concerns such as the following.
“I want to know how other companies are using their machines effectively.”
“We are struggling with 100% inspection of large volumes of workpieces…”
“Rising labor costs mean we need to reduce machining and inspection man-hours as much as possible…”
In this article, we explain how to operate a “CNC automatic lathe” effectively in order to maximize the benefits of its introduction.
Detects dimensional errors of pipes, reducing the full inspection process.
The customer was using a CNC turret lathe but was experiencing accuracy problems with machined workpieces.
The cause was that chips became trapped between the workpiece and the chuck, allowing the workpiece to remain slightly lifted as it proceeded to the machining process.
While looking for a sensor that could be retrofitted to the turret lathe to prevent machining defects before they occurred, the customer consulted us after one of our sales representatives visited.
【Video】
Automatic Detection of Hole Machining Anomalies【the revolutionary customization of Cincom L12】
On-machine measurement of workpiece origin setting and post-processing dimension measurement
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CNC automatic lathes, what you ABSOLUTELY need to know for MAXIMUM use?
This article explains the Citizen Machinery CNC automatic lathe Cincom series, which Metrol also uses.
・We want to advance NC adoption in our machining department.
・We want to eliminate machine troubles and minor stoppages to improve operating rates.
・We want to consolidate processes and streamline upstream and downstream steps such as inspection.
It is recommended for those with these goals in mind.
