Key CNC Machining Terms Every Machinist Should Know

If you’re just starting to get involved with CNC machining, understanding what CNC machining is, along with its lexicon, isn’t just beneficial; it’s a must. There are very specific CNC machining terms used in every aspect of the manufacturing space. You’ll hear them used in small machine shops to large manufacturing companies like JetCrafted.

Learning the lingo will make it easier for aspiring operators, designers, and machinists to communicate effectively, and accurately share ideas with their peers.

This post will serve as your introduction to the terminology, highlighting key basic industry terms for CNC machining every professional should know. We’ll cover everything from machine components to machining processes, providing a solid foundation for those of you eager to learn more about this vital aspect of modern manufacturing.

Terminology Used in CNC

The first term you’ll encounter when getting into manufacturing and machining is CNC. CNC stands for Computer Numerical Control, and it’s this technology that revolutionized the way we use machine tools to produce parts.

The CNC machine terminology isn’t just a random collection of industry jargon. It serves as the very language that brings together design with production. For instance, when discussing the ‘machining process,’ one refers to the method by which material is removed from a workpiece to get the desired shape and dimensions.

The vocabulary has expanded from the early days of numerical control, where punch cards were used to guide machines, to today’s advanced CAD/CAM software that translates digital designs into detailed machine instructions.

In essence, the specialized vocabulary used in CNC machining not only communicates the technical aspects of the process but also embodies the precision and innovation that CNC technology brings to modern manufacturing.

CNC Terminology and Definitions

The following terms form the basic language CNC professionals use when discussing the components and techniques frequently used in the industry. You won’t be able to get far if you don’t know basic words like ‘axes’, referring to the directions of movement, and ‘G Code,’ the programming language.

Knowing machining terms such as ‘end mill,’ ‘fixture,’ and ‘tolerance’ will help you understand how machines achieve precision and design intricacies. It will also make it easier to communicate with experts in the field and understand technical documentation and software applications.

G code

So, what is G code in CNC machines? It’s the foundational language that guides the machine’s movement and operations. It decides where and how the cutting tool moves, including its speed and path. Without this code, there would be no way to do precise cuts and shapes or translate a designer’s intent into physical parts.

Here are some of the G Code commands used in CNC machines:

M code

What is the M code in CNC machines? It’s an additional programming language used alongside G code in CNC machining to control machine functions. These codes command the machine to perform specific actions, such as starting up the spindle and opening and closing the chucks. 

Feed Rate

The feed rate in machining operations is the velocity at which the cutting tool interacts with the workpiece. It is measured in units per minute and it affects the quality of the cut, tool wear rate, and the overall efficiency of the machining process. An optimized feed rate is the key to a high production rate and a long lifespan of the cutting tools.

CAD CAM Software

CAM computer aided manufacturing and CAD computer aided design software are a big part of modern CNC machining. CAD software enables the creation and modification of part geometries, while CAM software translates these geometries into executable machine code commands (G code and M code).

Toolpath

CNC Toolpath is the programmed route that the cutting tool takes during a CNC machining process. It directly influences the final surface finish and dimensional accuracy of the final part.

Toolpaths can have linear, circular, or complex contours. The selection of the appropriate toolpath type is vital for achieving desired part geometries and can include strategies like contouring, pocketing, and drilling.

Axis X

In CNC machines, the X-axis is the horizontal movement parallel to the work surface. It’s one of the primary axes that define the motion of the cutting tool. Having precise control over the movements along the X-axis is key for shaping the workpiece. It affects the accuracy and finish of the machined part.

Axis Y

The Y-axis is the linear axis perpendicular to the X-axis, typically representing vertical movement. It works alongside the X and Z axes to position the tool or workpiece. Having complete control over the Y-axis movements is crucial for achieving the desired dimensions and geometries in multiaxial machining operations.

Axis Z

On a CNC machine, the Z-axis signifies the vertical movement, or depth, allowing the cutting tool to approach the workpiece from above. It plays a pivotal role in determining the depth of cut, which affects the removal rate and the part’s final dimensions. Precise Z-axis control is a must for operations such as drilling and pocketing.

Spindle Speed

Spindle speed is measured in revolutions per minute (RPM) and refers to the rotation rate of the machine’s spindle. It’s critical in machining as it affects the quality of the cut and tool life. Spindle speed and feed rate are determined by the machining material, the tool type, and the desired surface finish.

Rapid Traverse

Rapid traverse is the maximum speed at which a CNC machine moves its tools when they’re not cutting. This movement minimizes non-productive time by quickly positioning the cutting tool to the start point of a toolpath or moving it away after it’s done. 

So, in short, what does rapid traverse do? It contributes to overall efficiency and reduced cycle times in CNC machining operations.

Cutting Tool

Every CNC machine uses cutting tools to remove material from a workpiece. They are usually made of durable materials and have specific shapes that help them remove material from the workpiece. You can select the right cutting tool by following the below-listed criteria: 

• Tool Material. The cutting tool’s material (e.g., high-speed steel, carbide, ceramic).

• Tool Geometry. The cutting tool’s shape and design (e.g., end mill, drill bit, lathe tool).

• Coating. Optional coating is applied to the tool to increase durability, reduce friction, and improve performance.

• Depth of Cut. The depth of material that the cutting tool removes in a single pass. It affects cutting forces and tool wear.

Tool Radius Compensation (TRC)

Tool Radius Compensation (TRC) is a CNC feature that adjusts the toolpath for the actual cutting radius of the tool. It’s how you can ensure dimensional accuracy, especially for intricate profiles. TRC allows CNC machines to produce parts with precision without manual adjustments to the program.

Tool Length Offset (TLO)

Tool Length Offset (TLO) is a parameter in CNC machining that compensates for the varying lengths of different tools. It ensures that the cutting tool works at the correct distance from the workpiece, maintaining the desired depth of cut and accuracy. 

Work Offset (WO)

Work Offset (WO) in CNC is a setting that determines where the workpiece starts in the machine’s coordinate system. It ensures the correct positioning of the toolpath on the workpiece. WO is crucial for repeatability and accuracy, allowing the machine to reference the correct starting point for each operation.

Workpiece

In CNC machining, a workpiece is the raw material that is fixed to the machine table and shaped into the final part. Preparing a workpiece means selecting appropriate material, securing it properly, and determining the starting point for machining. Other things you need to consider include material properties, size, and the final geometry.

Chip Load

Chip load is the amount of material removed by a cutting tool’s edge in one revolution, impacting both tool life and surface finish. Correct chip load ensures efficient cutting, prevents tool breakage, and achieves a quality finish. It’s calculated based on the cutting tool’s diameter, the number of flutes, and the feed rate.

End Mill

End mills are rotary cutting tools with multiple cutting edges used in milling operations to shape workpieces. They perform various operations from profiling to roughing and finishing. Also, they come in different shapes and sizes to match specific tasks. End mills can be chosen based on the workpiece’s material and the operation’s complexity.

Ball Nose End Mill

Ball-nose end mills are a type of end mill with a hemispherical tip. They’re used for 3D contouring or smooth finishing in CNC machining, especially on complex surfaces and tight spaces. Their rounded tip minimizes chipping and provides a smoother surface on the final part.

Flat Nose End Mill

Flat-nose end mills have a flat bottom and are used for making slots, straight cuts, and general-purpose milling. They’re chosen for applications requiring sharp, square corners at the bottom of grooves or for machining flat surfaces. Their precise cutting edges make them suitable for producing clean and accurate cuts.

Chamfer

A chamfer is an angled edge or corner typically cut at 45 degrees to eliminate sharp edges. Having smooth edges makes assembly or welding easier. Many chamfering methods exist and they have different applications. Those include manual chamfering with hand tools, machining with chamfer mills, and automated processes using CNC machines.

Pocket

A pocket is a recessed area or cavity cut into the surface of a workpiece. Pockets can vary in shape and depth and are created using end mills or specialized cutting tools controlled by a CNC program to follow a predetermined toolpath.

Slot

Slots are narrow, elongated cutouts or channels in a workpiece. Making these slots often requires the use of end mills or slitting saws. CNC machines can perform slotting with high precision by following a programmed path to achieve the desired width and depth.

Thread

Threading in CNC machining involves creating a helical ridge or thread on the surface of a cylindrical workpiece for fastening purposes. Tools such as taps for internal threads or dies for external threads are used in CNC lathes or mills programmed to produce accurate and consistent threads.

Lathe

A lathe in CNC turning is a machine tool that rotates the workpiece on its axis while it’s shaped by a stationary cutting. CNC lathes are used to perform precise operations like cutting, knurling, drilling, and threading.

Chuck

A chuck on a CNC lathe is a clamping device that securely holds the workpiece during machining. Chucks come in various types: three-jaw (universal), four-jaw (independent), and collet chucks.

Toolholder

Tool holders secure the cutting tools in the spindle of a CNC machine and help them keep the correct positions. They’re the best way to keep everything precise and reduce vibrations during machining. Common types include collet chucks, end mill holders, and shrink-fit holders.

Roughing

Roughing is the first stage of any CNC machining process, where large amounts of material are rapidly removed from the workpiece. The purpose is to create a rough shape close to the final dimensions, using tools that can withstand high cutting forces and speeds. They lay the groundwork for finishing operations.

Finishing

Finishing in CNC machining is the final stage, where a workpiece is refined to the needed dimensions and surface finish. It involves lighter cuts with fine-grained cutting tools to achieve the required smoothness and tolerances, often with multiple passes for optimal quality.

Facing

Facing operations in turning and milling involves cutting the surface of a workpiece to produce a flat area. In turning, a lathe’s cutting tool moves perpendicularly to the workpiece’s rotating axis, while in milling, a face mill or end mill creates a flat surface by moving over the workpiece.

Turning

Turning in CNC machining refers to a process where a workpiece is rotated on a lathe while a stationary cutting tool shapes it into a desired form. The expected outcomes of CNC turning are round components with high accuracy and consistency.

Boring

Boring in CNC machining is an operation that makes a hole or a cylindrical cavity in a workpiece bugger. It’s done using a single-point cutting tool or a boring head. This operation is essential for achieving precise hole sizes, straightness, and surface finish in components and is frequently applied when trying to create highly accurate internal diameters.

Jig

A jig is a custom-made tool used in CNC machining to control the motion and position of another tool, ensuring precision and repeatability. It securely holds and locates the workpiece, guiding the cutting tool for accurate machining operations.

Fixture

Fixtures in CNC machining are devices used to position and support the workpiece during operations securely. Unlike jigs, fixtures do not guide the cutting tools but ensure the workpiece remains in the correct orientation. Without this stabilization, it’s hard to maintain accuracy, especially during complex or high-speed machining processes.

Clamping

Clamping in CNC machining secures the workpiece to the machine’s table or a fixture. Proper clamping prevents movement of the workpiece due to the forces exerted during machining. It ensures accuracy, prevents damage, and maintains safety during the cutting process.

Offset

Offsets in CNC machine programming are adjustments made to account for variations in tool geometry, wear, and workpiece positioning. They allow machinists to fine-tune the toolpath for precise control over the dimensions of the final part. You need to do the occasional offset adjustments to achieve the desired tolerances and part specifications.

Automatic Tool Changer (ATC) 

A system used in CNC machines that automatically changes the cutting tools as needed during the production process. It’s the best way to improve speed and efficiency as it minimizes manual tool changes, thus reducing downtime and the potential for human error. 

CNC Controller

A CNC controller is a device that coordinates the movements and functions of the machine according to the programmed instructions. It interprets G-code and converts it into electrical signals to control the motors and other actuators, ensuring precise movement along the designated toolpath.

The table below shows some of the key specifications of a CNC controller.

Bevel

A bevel in CNC machining refers to an edge that is cut at an angle that is not 90 degrees to the face of the workpiece. This angled cut is often used to prepare edges for welding, to enhance aesthetic appeal, or to reduce sharp edges for safety. 

Creating a bevel requires precise control of the machine’s cutting tool to achieve the desired angle and to ensure uniformity across the part’s surface.

Kerf

Kerf is the term used to describe the width of material that is taken away by cutting. In CNC machining, it specifically refers to the width of the cut made by the cutting tool. The size of the kerf is important as it affects the cut’s precision and the part’s final dimensions. 

Undercut

An undercut is a recessed area that’s difficult to machine with standard tools due to its inaccessibility. It is typically hidden or tucked away beneath an outward-facing surface or feature. To successfully create these features without compromising the integrity of the workpiece, you need to use specialized strategies, such as using custom tools or adjusting the machining approach.

Drilling

Drilling is the process of creating round holes in a workpiece using a rotating drill bit. This operation is executed precisely by a CNC machine, which guides the drill bit at the correct speed and depth according to the programmed instructions. 

Drilling is a fundamental and widely used process in manufacturing for creating holes for fasteners, channels for wiring, or spaces for mechanical components.

Milling

Milling is a versatile CNC machining process that involves removing material from a workpiece using a rotating cutting tool called a mill or end mill. The CNC machine moves the tool across the workpiece in various directions, creating a wide range of shapes, slots, holes, and other features.

Turning

Turning in CNC machining is the process of shaping a rotating workpiece by applying a cutting tool to its surface. This method is used to create cylindrical parts with precise diameters and smooth finishes. Turning operations can include cutting straight lines, grooves, tapers, and other workpiece features.

In Summary

Anyone involved in the manufacturing industry, from novices to seasoned machinists, must put in the effort to learn its specific jargon. Knowing CNC machining terms makes communication, workflow, and precise execution of machining tasks much easier. 

These specific terms are part of every machining stage, from the planning to the execution, and relay important information. The more CNC terms you know, the better you’ll be at designing, using, and troubleshooting. It’s the first step to becoming a CNC master, boosting production, and staying ahead of the curve.

FAQs

1. Why is understanding CNC terminology important for machinists?

Understanding CNC terminology is crucial for machinists to accurately read blueprints, set up machines, and communicate effectively in the manufacturing environment, ensuring precision and efficiency in production.

2. What is the difference between G code and M code?

G code is a programming language for CNC that instructs the machine on movements, like paths and speeds. M code controls machine functions such as coolant flow or spindle on/off, handling the operations not covered by G code.

3. What are the different types of cutting tools used in CNC machining?

CNC machining utilizes various cutting tools, including end mills for milling, drill bits for drilling, lathes for turning operations, and ball screws for precise linear motion.

4. What are some resources I can use to learn more about CNC machining terms?

You can learn even more about CNC terms by visiting the websites of large manufacturers like JetCrafted, consulting CNC machining textbooks and manuals, and participating in CNC forums and communities. For those interested, many resources are available online and in real life.