A computer numerical control (CNC) lathe is a versatile machine that can be used to make different parts from metals using operations such as turning, facing, and grooving.
It is one of the most widely used machine tools in subtractive manufacturing.
The primary function of a CNC lathe is to turn axisymmetrical parts with high accuracy. You can also use it for cutting threads, drilling holes, and milling shapes.
Although traditional lathes can perform similar functions, CNC lathes outperform them in terms of quality, repeatability, and speed.
So what are the elements that set a CNC lathe apart from a traditional lathe? And what are the steps involved in operating a CNC lathe?
This article provides a detailed guide to CNC lathes while explaining their workflow and shedding some light on their practical applications.
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What is a CNC Lathe? Explained
CNC lathe is a modification in which a traditional lathe is integrated with a computer system. In this machine, the workpiece rotates at high speed, and a computer-controlled cutting tool machines the workpiece to produce axisymmetric parts with high accuracy. It can be used for machining various metals and non-metals.
Mainly they are available in horizontal or vertical configurations. Both can have a varying axis setup.
Modern CNC lathes have 3, 4, 5, or more axes systems, making them the perfect choice for machining complex geometries within a short cycle time.
They perform CNC turning operations on materials and are used for various manufacturing applications, ranging from high-precision airplane parts to regular kitchen utensils.
Depending on their configurations, CNC Lathes can be used for various operations like cutting, drilling, shaping, and turning.
Workflow of a CNC Lathe: 4 Steps
From preparing your design to finally manufacturing it on a lathe, the following is the workflow in most CNC lathes.
CAD Phase (Plan to Design)
The very first step in operating a CNC lathe is to prepare a design that exactly replicates the final product.
There are various CAD software like Blender, Catia, Autodesk Fusion 360, etc., which can be used for making 3D STL designs for turning operations.
Although all CAD file formats can be used for machining, they might need some post-processing to make them compatible with a CNC lathe.
Generally, IGES file format is used with CNC lathes, and therefore all the design files should be converted to IGES to execute the turning process.
Once the design is ready, you have to decide on the machine's configuration that you will use to cut the material.
CAM Phase (Design to Code)
Preparing CAD design for CNC Lathe is a process that involves converting the design into G-codes, a format that the machine can read.
There are many different types of CNC lathe machines, and each has specific requirements depending on its number of axes.
In the CAM phase, the design is converted into code using dedicated software or manual programming.
Whereas manual programming requires a good understanding of part drawing and the corresponding G-codes.
There are various G-code editors that can be used for writing the code or modifying an existing code.
These program codes are like ordered commands that tell the CNC machine what to do and how to do it.
Preparing the design for turning is a process involving many different steps. The first step is to determine the desired material, usually wood or metal.
Depending on the stock material and size, you will program the lathe with customized G-codes and M-codes.
G-codes contain offset-based settings that are used to control the lathe's movements. This includes G0s, rapid, G1, speed, etc.
M-codes control optional machine settings like coolant on/off, unclamping the chuck, bringing up the part catcher, etc.
Important Parameters for Programming a CNC Lathe
Note that a CNC lathe will identify the location and size of the workpiece based on the coordinates assigned in the program.
Following are some important lathe-specific program codes that are commonly used while programming a lathe.
|X0||Center of the part|
|Z0||The face of the part|
Anything you reduce from the part will be Z- (negative)
|G50||Used to limit spindle speed|
|G96||Automated speed adjustment depending on stock size|
|G97||Turns at a constant speed set by the operator|
|G71||Rough turning canned cycle|
|G70||Finish turning canned cycle|
|U||Incremental for X|
|W||Incremental for Z|
Lathe specific G-codes
Control Phase (Code to Part)
The control phase of a CNC lathe is one of the most important elements of its workflow because it determines the quality and accuracy of the final product.
Here we control both the machine and its cutting tools. Lathe cutting tools include various types of tools with specific geometries ideal for a particular machining process.
Following is the step-by-step process involved in setting up your CNC lathe for the job:
- Once you turn on the CNC lathe, the first thing to do is position the tool to zero. Here the cutting tool is brought back to its origin point along the XY axes.
- Then install the workpiece on the spindle. The stock material you use should be longer and wider than the part you plan to make.
- Tighten the chuck and lock it in place. You can set tooling next.
- There are many different cutting tools for lathes. The type of cutting tool you need will depend on the material, its hardness, and the application.
- The most common types of cutting tools are High-Speed Steel (HSS), Tungsten Carbide (TCT), Cobalt, and Molybdenum Disulfide (MoS2).
- The selection of tools will also depend on the machining operations you want to perform.
- Once the workpiece and tools are in place, you can load the program file to the controller of the machine.
- You can use the inbuilt file explorer in your CNC lathe to select the program from a local directory or send it from a computer.
- Once the program is imported, you must set up the work and tool offsets.
- You can accurately set up the Z-axis by manually facing the workpiece using the lathe and recording the coordinates.
- To set the X-axis, you can manually turn the outer diameter of the workpiece and record the final coordinates.
- Now you have the zero position of the workpiece.
- Once all the above steps are completed, you can run the job. However, it is important to monitor the process to avoid accidents.
Post-processing the Part
The post-processing of lathe machined parts consists of a roughing operation, followed by a finishing operation.
Roughing operations are only required if the part has any excess material that could not be removed during the turning operation.
You can either use a lathe to perform this roughing operation manually or by using a grinder wheel.
The finishing operation is performed to enhance the surface finish of metal parts to produce a smoother and shinier workpiece.
You can polish it in one of three ways: by using emery paper, abrasive paste, or polishing compounds.
Once you complete these processes, the part will be ready to use or for further paint jobs.
Types of CNC Lathes
CNC Lathes can be mainly classified as horizontal and vertical lathes.
In vertical lathes, the workpiece and cutting tools lie vertically, but in a horizontal lathe, they are in a horizontal position.
Vertical CNC turning centers are used to work on heavy parts and will also have live tooling for milling on the workpiece.
Horizontal CNC lathes are used for almost all generic applications. They are the most employed lathes and have a simple operation.
Apart from the orientation, CNC lathes can also be classified based on their size as mini lathes, midi lathes, and full-size lathes.
Parts of a CNC Lathe
The main parts of a CNC lathe consist of a controller unit, bed, headstock, tailstock, tool holder, work holder, etc.
Mostly the headstock on a lathe is located on the left side of the machine.
The spindle is the main component in a headstock. It turns the workpiece with the help of a powerful spindle drive.
Normally, on CNC lathes, servo motors are used to drive the spindle.
The tailstock is used in a CNC lathe to support the workpiece axially.
It provides extra support for working on long workpieces.
On CNC lathes, 3-jaw hydraulic chucks are normally used to hold the workpieces.
They can hold hollow and solid workpieces with the help of OD (outer diameter) and ID (inner diameter) clamping jaws.
Other work-holding devices like a 4-jaw chuck, collet, faceplate, etc., are also used, depending on the shape of the workpiece.
The turret is the tool carrying part in a CNC lathe. It can store multiple tools that you can use for various operations.
It can be loaded with tools for turning, grooving, threading, etc., and also with internal tools like boring bar, drills, etc.
The machine bed on a lathe is a solid metal structure supporting other moving components like the tool post, tailstock, and headstock.
It is mostly made of strong, sturdy materials like cast iron.
Machine Control Unit (MCU)
The MCU in a CNC lathe includes a controller, screen, input switches, etc. The controller is the processing unit of any CNC machine.
The MCU system works with software. Common software systems used with CNC lathes are FANUC, Hass, Siemens, Hydro-Dyne, and Mitsubishi.
MCU can be linked to a computer or used independently, depending on their capabilities.
Foot pedals or foot switches are controls that CNC machine operators can use with their feet.
Generally, these controls allow you to quickly activate and deactivate the work holding and tailstock support.
Things You Should Know Before Buying A CNC Lathe Machine
Before purchasing a CNC lathe machine, you should consider the following things:
The Intended Use of the Machine
Consider the materials and tools you plan to work with. It will depend on the operations you want to perform and the parts you want to make.
For example, if you want to tap holes in the turned parts, you'll need a CNC lathe with live tools.
The Work Area
The work area is an important factor to consider as it greatly affects the things you can make.
Note that as the work area increases, the machine's footprint also becomes larger. So make sure you have enough room for the machine.
Can you Operate a CNC Lathe?
The operation of CNC lathes is significantly different from traditional lathes.
These lathes consist of computer programming that controls the various actions of the machine.
Therefore, to operate a CNC lathe, you need to be familiar with the workflow and software involved in its operation.
You can either learn from the resources manufacturers provide or get help from tutorials curated by professionals.
Belt Drive or Direct-Drive Spindle?
If you are looking for a short work cycle, go with a lathe having a direct-drive spindle. It allows you to change the spindle RPM with a rotary switch.
Belt-drive spindles need manually switching the belt between different pulleys to change the spindle speed.
A belt-driven spindle will do the job if your application only requires a stable RPM throughout the machining process.
Speed, Power, and Torque
The speed, power, and torque required for a CNC lathe depend on the workpiece diameter.
Generally, workpieces with larger diameters are turned at low speed and high torque configuration.
The price of the machine is also an important factor. Generally, desktop and benchtop lathes are priced lower than large industrial-grade lathes.
You should also consider additional costs that will be incurred in the form of accessories, tooling, software, maintenance, etc.
Verify with the manufacturer what type of support you can expect from them. Most manufacturers will provide after-sales support with a standard warranty.
Choose one with a large and active community as you can also get help from others using similar machines.
Applications of CNC Lathes
A lathe with a CNC capability allows you to turn cylindrical and non-cylindrical geometries like slots, keyways, hex shapes, etc.
They are primarily employed in woodturning and metal turning applications.
With the addition of live tooling on a CNC lathe, you can even mill and drill holes on the machined parts.
CNC lathes can be used to create various items such as crankshafts, screws, gun barrels, spindles, table legs, baseball bats, workshop tools, and other similar items.
The major advantage that CNC lathes offer over other machines is their high-quality and quick cycle time for machining axisymmetric parts.
This makes them ideal for mass-production applications where high output volume with quick cycle time is desirable.
CNC lathes are the most commonly used machine for metal turning. They can process many different metals and are capable of performing a variety of operations on them.
They have excellent accuracy and require less operator input than other machines, which reduces training time and lowers the cost per part.
Though they are good at turning parts, it is also important to consider their limitations.
Lathes, in general, are limited to turning items that can be held between centers. This means they cannot cut out shapes from flat stock or turn irregular shapes.
They are also not very well suited for deep hole drilling or tapping, but they excel at making shallow cuts in round stock.
Frequently Asked Questions (FAQ)
What is the difference between CNC lathe and CNC turning centers?
The difference between CNC lathes and CNC turning centers is that CNC lathes can only turn and shape cylindrical workpieces. At the same time, you can use CNC turning centers for turning and milling operations.
How is a CNC lathe different from a manual lathe?
CNC lathes are computer-controlled machines that use a program to control the cutting process. They can work with metal and other materials with a high rate of repeatability as they can be programmed to follow a specific pattern. Manual lathes are controlled by the operator using hand tools. They are not as precise or powerful as CNC lathes, but they are more flexible because they can perform different operations without the need for programming.