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CNC Machining Terms to Know

CNC Machining Terms to Know

CNC (Computer Numerical Control) machining is a pivotal technology in modern manufacturing, offering precision and efficiency in producing parts. For those new to the field or looking to deepen their understanding, familiarizing yourself with key CNC machining terms is essential. Here’s a guide to some crucial CNC terminology.

  1. Absolute Programming

In CNC machining, absolute programming refers to a coding method where all coordinates are defined relative to a fixed origin point. This method simplifies programming by eliminating the need to calculate distances from any point other than the origin. The G90 code is used to set a machine to absolute mode.

  1. Axis

In CNC machining, the axis refers to the direction in which the machine operates. CNC machines are typically categorized by the number of axes they have, such as 3-axis, 4-axis, or 5-axis machines, with each additional axis allowing for more complex and precise movements.

  1. Backlash

Backlash is the slack or lost motion that occurs when direction is reversed in a machine component. It is crucial to minimize backlash to maintain precision in machining operations, particularly in high-precision environments.

  1. Boring

Boring is a machining process that enlarges an already existing hole. It is performed using a single-point cutting tool called a bore, which allows for precise control of the hole size and finish.

  1. Chip Load

Chip load is the amount of material removed by each tooth of a cutting tool per revolution. Managing chip load is critical for maintaining tool health, achieving good surface finish, and ensuring efficient material removal rates.

  1. CNC Lathe

A CNC lathe is a machine that rotates the workpiece on its axis to perform various operations like cutting, sanding, knurling, drilling, or deformation with tools that are applied to the workpiece to create an object with symmetry about an axis of rotation.

  1. Clockwise Interpolation

Clockwise interpolation is a method of creating circular or arc movements in a clockwise direction using a CNC machine. This movement is controlled by the G2 command, which directs the cutting tool along a specified path.

  1. Coolant

Coolant in CNC machining is used to keep the cutting tool and workpiece at a stable temperature and to remove chips from the cutting area. It can prevent tool wear and failure, thereby extending the tool’s life and improving the finish of the machined part.

  1. Counterclockwise Interpolation

Similar to clockwise interpolation but in the opposite direction, counterclockwise interpolation involves moving the cutting tool along an arc in a counterclockwise direction. This is controlled by the G3 command.

  1. Cutter Compensation

Cutter compensation is a feature used in CNC programming to adjust the toolpath for variations in tool diameter, wear, and deflection. This ensures that the part dimensions remain consistent, even with tool changes.

  1. Cutting Tool

A cutting tool is any tool that is used to remove material from the workpiece during machining. Examples include drills, endmills, and reamers, each designed for specific types of cuts and materials.

  1. Cycle Start

The cycle start is a command, typically initiated by pressing a green button on the CNC controller, that begins the execution of a CNC program.

  1. Dwell

Dwell refers to a pause in the tool’s motion at a specific position, often used to allow for more precise machining, such as when a hole is being bored. During dwell, the tool maintains contact with the material without advancing, ensuring better accuracy and finish.

  1. End Mill

An end mill is a type of milling cutter, a cutting tool used in industrial milling applications. It is distinguished from the drill bit in its application, geometry, and manufacture. End mills are used in milling applications such as profile milling, tracer milling, face milling, and plunging.

  1. Feed Rate

Feed rate refers to how quickly the tool moves through the material. It is usually measured in inches per minute (IPM) or millimeters per minute (mm/min). Optimizing feed rate is crucial for maximizing productivity and minimizing wear on the tool.

  1. Fixture

A fixture is a device used to securely hold the workpiece in place during machining. Proper fixture setup is essential for achieving precise machining operations and preventing workpiece movement during the cutting process.

  1. G-Code

G-Code is the fundamental language used to control CNC machines. It consists of commands that dictate the machine’s movements and operations. Knowing how to interpret and modify G-Code can be incredibly valuable for troubleshooting and optimizing manufacturing processes.

  1. Helix Angle

The helix angle in an end mill is the angle between the edge of the helix and the end mill’s axis. This angle affects the cutting efficiency and the load distribution on the tool. End mills with different helix angles are used based on material properties and specific cutting needs.

  1. Incremental Programming

In incremental programming, each move is based on the position of the tool at the end of the previous move, rather than from a fixed origin. This is coded with G91 and is useful for repetitive tasks or patterns within a program.

  1. Linear Feed

Linear feed is a basic motion in CNC programming used to move the cutting tool along a straight line at a specified feed rate. It is coded as G1 and is one of the most commonly used commands in CNC machining.

  1. M-code

M-code is used in G-code programming to control miscellaneous functions of the CNC machine, such as coolant flow, spindle start/stop, and tool changes. Each M-code serves a specific operation, essential for automating the machining process.

  1. Machining

Machining is a broad term that encompasses all processes in which material is removed from a workpiece to achieve a desired shape, size, or finish. It includes operations such as milling, turning, drilling, and tapping.

  1. Machinist

A machinist is a skilled technician who operates CNC machines and performs setups, understands tooling applications, and ensures machines produce parts to specified tolerances and finishes.

  1. Peck Drilling

Peck drilling is a technique used to drill deeper holes with intermittent cutting. The drill bit extends a short distance into the material, retracts to clear chips, and then advances further. This process helps prevent tool breakage and overheating.

  1. Rapid Traverse

Rapid traverse is a command (G0) used in CNC machining to move the tool to a specified position as quickly as possible without cutting. This is used to minimize non-productive time during machining operations.

  1. Reamer

A reamer is a type of cutting tool used to improve the finish and size of a hole that has already been drilled. It removes a small amount of material to ensure the hole’s diameter is highly accurate and smooth.

  1. Rotary Table

A rotary table is a precision work positioning device used in metalworking. It allows the operator to cut or drill at exact intervals around a fixed axis, enhancing the versatility and capability of a milling machine.

  1. Roughing and Finishing

Roughing refers to the initial phase of machining where most of the material is removed at a higher feed rate but lower precision. Finishing follows roughing and involves slower feeds and speeds to achieve the final dimensions, tolerances, and surface finishes.

  1. Setup

In CNC machining, setup refers to the process of preparing the machine for operation. This includes loading tools, setting zero and reference points, positioning the workpiece, and configuring the software settings. Effective setup is critical to ensure operational efficiency and accuracy.

  1. Spindle Speed

The speed at which the spindle rotates, typically measured in revolutions per minute (RPM). Adjusting the spindle speed is vital for the tool’s performance and longevity, as well as the quality of the cut. Proper spindle speed settings depend on the material being machined and the type of tool used.

  1. Stepover

Stepover is the lateral distance between passes of a cutting tool. Adjusting the stepover rate can influence the finish of the part and the overall machining time. Smaller stepover values increase the surface finish quality but require more passes, thus increasing machining time.

  1. Subtractive Manufacturing

This term refers to the process of creating objects by successively cutting material away from a solid block, i.e., subtracting material. CNC machining falls under this category, contrasting with additive manufacturing like 3D printing.

  1. Surface Finish

Surface finish refers to the texture and smoothness of the surface of a machined part. It is an important quality attribute, affecting the mechanical and aesthetic properties of the part. Surface finish measurements are typically specified by Ra values, which indicate the roughness average.

  1. Tapping

Tapping is a process of cutting internal threads in a hole using a tool called a tap. It is essential for preparing holes to receive threaded fasteners like screws or bolts.

  1. Tolerance

Tolerance refers to the allowable limit of variation in a physical dimension. Tight tolerances are often critical in high-precision industries like aerospace and medical devices. Understanding how to achieve and measure these tolerances is crucial for ensuring part functionality and compatibility.

  1. Tool Path

The tool path is the programmed route that the cutting tool follows to remove material from a workpiece. It is critical for defining how a part is machined and is essential for ensuring the quality and accuracy of the final product.

  1. Work Coordinate System (WCS)

The work coordinate system is a reference frame defined on the CNC machine that establishes the origin for part location. Multiple coordinate systems (G54 through G59) can be set up for complex setups or multiple parts.


Mastering these CNC machining terms will not only enhance your technical expertise but also enable you to communicate more effectively in the manufacturing industry. Whether you are troubleshooting a process or discussing specifications, a solid grasp of these terms can help you navigate the complexities of CNC machining with confidence.

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