Turning operations can be performed either manually or using computer-controlled machines.
The use of CNC turning machines in the manufacturing industry has been on the rise as it offers several advantages over manual turning.
One of the most notable advantages is that CNC turning is much faster than manual turning.
CNC turning machines can do the same job in less than half the time that would take a person to do it manually, thereby increasing productivity and reducing cost.
CNC turning is a machining process that uses computer-controlled turning machines like a lathe or turning center to produce parts. CNC turning process is preferred when high precision, repeatability, and surface quality are required in machined parts.
This article discusses CNC turning by looking at its working principles, configurations, operations, applications, and more.
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CNC Turning Explained
Fundamentals of CNC Turning
CNC Turning is a subtractive CNC manufacturing process used to work on cylindrical, conical, or elliptical-shaped materials.
This process requires a CNC machine that can rotate the workpiece or stock material at high speed while the cutting tool cuts the rotating material.
The cuts can be internal or external. For internal cuts, internal diameter (ID) turning tools are used, and outer diameter (OD) tools are used for external cuts.
However, certain turning machines like wood lathes consist of a hand-held tool that cannot be automated with a computer numerical control system (CNC)
CNC Turning System
Some of the basic components of a CNC turning system are the part program, machine control unit, and the turning machine (lathe).
The part program is a computer-generated program code used to control the CNC lathe.
This program has the toolpath information and commands for controlling the speed, feed, coolant on/off, etc. It is fed to the machine control unit (MCU).
MCU itself is a microcomputer. It processes the program code and sends electrical signals to the programable lathe or turning machine.
Finally, the machine turns and carves the workpiece as programmed by the computer.
CNC Turning Machine (Lathe) - Components, Working
The most basic components seen in CNC turning centers or lathes are chuck, spindle, spindle motor, transmission (belt drive, lead screw, etc.), cutting tool, tool holder, servo motor, etc.
|Spindle||Rotates the workpiece|
|Spindle motor||Powers the spindle|
|Chuck||Tightly holds the workpiece|
|Cutting tool||Physically cuts the workpiece|
|Tool holder/post||Holds the cutting tool|
|Transmission drives||Moves the machine parts like tool post|
|Stepper or servo motor||Powers the transmission|
Different components of a CNC turning machine and their objective
A CNC lathe turns stock materials into precise shapes with complex cross-sections through a process called turning.
During its operation, a CNC lathe holds the workpiece using the chuck fixed to the headstock/spindle.
A spindle motor powers the headstock. It helps the machines rotate or turn the workpiece at high speeds.
Cutting tools are fit to a tool turret or a tool post that is driven by feed screw transmission mechanisms like a lead screw or ball screw.
The cutting tool moves along a linear axis and makes desired cuts when the workpiece is turned.
Some CNC lathe machines will also have a tailstock to support the workpiece during the machining process.
A standard CNC lathe will have two linear axes and a rotational axis.
The two linear axes are Z and X, these are the axes of movement of the cutting tool, and the workpiece rotates in the RZ axis.
Depending upon their material capability, lathes can be classified as wood lathes and metal lathes.
Although a wood lathe can be used for machining metal, it does not produce the optimal results.
Different Configurations of Lathe or Turning Center
CNC lathes and turning centers can have a horizontal or vertical configuration.
Horizontal laths hold the workpiece horizontally from a side (left or right). Vertical lathes hold the workpiece from the bottom in an up-down configuration.
How's a Turning Center different from a Lathe?
Turning centers essentially are lathes, but what makes them different is the additional live tools that allow them to perform milling and drilling operations.
Most turning centers have an enclosed setup and are used for heavy machining applications.
Types of Turning Operations in Machining
A CNC lathe or turning center can perform many tasks such as threading, facing, reaming, drilling, parting, surface finishing, etc.
Face Turning (Facing)
In face turning or facing operation, the cutting tool cuts the rotating workpiece in a right-angled direction.
Here, the cut is made at the face of a workpiece.
The cutting tool makes straight, curved, or angled lines on the rotating workpiece in knurling operation.
It's mainly used to make hand tool grips, barrel bars, gripped controller knobs, etc.
In threading operation, uniform helical screw threads are created on the workpiece.
Technically, a threading operation performed on a CNC lathe or turning machine is called single-point threading.
Most CNC software supports canned cycles, which allows the operator to feed in the thread size, length, offset, etc., for threading operation.
In taper turning operation, the workpiece is cut in a way that the diameter of the stock material is reduced from the tip to a certain point.
Here, the taper length will be less than the tool's cutting edge length.
Reaming operations are performed using ID tools to make final cuts on the existing internal holes of a workpiece.
This operation is done to make accurate ID cuts on the workpiece.
Spherical turning, also known as ball turning, is an OD turning operation wherein a spherical ball-like shape is made on the workpiece.
Hard turning operation refers to any single-point turning operation performed on a material with a hardness value of more than 45 HRc (Hardness Rockwell C).
In polygonal turning, CNC lathes make polygonal cut shapes on rotating workpieces. Here special cutting tools are used to achieve the polygonal cuts.
In grooving operation, the workpiece is grooved up to a certain depth. The cut can be internal or external.
When the grooving operation is performed on the face of the workpiece, it's called face grooving.
In parting or part turning operation, a sharp cutting tool is slowly plunged into the rotating workpiece till a part of it is cut off.
This cutting operation is typically used to remove a machined part from the stock material.
CNC turning centers make round holes on the workpiece in a drilling operation. Here either the workpiece is turned or the drilling bit is rotated using a live tool.
In a boring operation, existing drill holes are further enlarged to a cylindrical or conical shape using a single-point cutting tool.
Alternatives to CNC Turning
Drill press lathe attachments are a popular alternative to CNC turning. These attachments can be used to retrofit the drill press for manual turning operations.
Unfortunately, such techniques can only be used for woodworking applications. Metal turning requires a rigid machine setup.
Applications of CNC Turning
CNC turning machines are used primarily to machine wood, plastic, and metal parts.
It has applications in aviation, automobiles, firearms, sports, furniture making, etc.
Sporting equipment like baseball bats can be easily made on a CNC lathe, but complex parts such as muzzle brakes (used in firearms) need a turning center with drilling and milling capabilities.
Frequently Asked Questions
What is CNC turning used for?
CNC turning is used to machine parts through subtractive manufacturing. Here a turned stock material is continuously cut to make out the desired shape.
What is the difference between CNC lathe and CNC turning?
The difference between CNC lathe and CNC turning is that CNC turning is a machining operation while CNC lathe is a machine used for performing CNC turning operations.
What tools are used in turning operations?
For turning operations, facing, forming, tapering, chamfering, boring, drilling, knurling, threading, and parting tools are used.