What is CNC Programming?

Published by GayaMadhusanka on October 23, 2023October 23, 2023

CNC programming is also known as Computer Numerical Control programming. Basically, the process of creating instructions or code is called CNC programming. These are very common to program well-known machines like CNC mills, lathes, or routers. In industry, uncommon machines like CNC Laser marking and Laser welding machines also use the same common codes.

CNC programming plays a crucial role in manufacturing. So, if you have knowledge about it always you have a plus point in the industry.

What is CNC Programming?

Basically, In CNC programming we give machining instructions or commands to machines. According to the manufacturing requirements you can write machining instructions as a code. Some codes are common for all the machines. But some are very special for particular machines. whatever the machine, you should consider the GD&T in your program.

There are two types of machines CNC and NC machines. However modern CNC machines are running with CNC programs. There are mainly two types of Codes to define the instructions. G-Codes and M-Codes are those two types. Other than that S-Code, F-Code, and T-Code are also some special codes in programming.

Today all the 3D modeling and product design software have facilities for CNC programs with some simulations. Those simulations give a better understanding of tool movements and the machining process.

How to Learn CNC Programming?

The CNC programmer must have a good understanding of the machine tool’s capabilities. You can use that knowledge to generate efficient and accurate CNC programs. CNC programming involves tasks such as selecting the appropriate tooling and setting up the machine and workpiece. Knowledge about the sequence of machining operations is also important. The programmer must consider factors like cutting paths, tool paths, feed rates, and any necessary tool changes or tool offsets. Basically, you should have proper knowledge about the machining process before learning the CNC programs.

As a CNC programmer, You should have proper knowledge about Engineering Drawings, GD&T, GD&T Symbols, Surface finish Symbols, and Surface Finish Requirements.

How to Practise CNC Programming?

As a first step, you can use the CAD software tool to generate G codes and Run the Machining Simulations. For example, you can use Solid CAM software or online G-Code Simulators. If you don’t have that facility it is always recommended to use a pen and paper and write manual programs. By the time you can practis real program with experiance CNC progamers.

G Code & M Code

Machine operators use G-code and M-code, two fundamental types of commands, to control machine tools in CNC programming.

What is G-Code?

G-code is a programming language used to control movements and actions. The extended form of the G-Code is the Geometric Code. It consists of a series of commands. That specifies different machining operations and parameters. G-codes define actions such as tool movements, spindle speed, feed rates, toolpath orientation, and coolant/Cutting Fluid control.

What is M-Code?

M-code (short for “miscellaneous code“) is another type of command. Unlike G-codes, which control the movement and machining operations. You can use M-codes to direct auxiliary functions or actions of the machine tool. Machine operators typically use M-codes for tasks such as tool changes, coolant control, spindle start/stop, and machine tool or spindle orientation.

G-Code Commands in CNC Programming

The following are the general G-Code Commands. There are some other commands which are specified for particular machines. Always recommend reading the machine manual before using a CNC machine.

Positioning Codes

G00 – Rapid Positioning: G00 is used for rapid, non-cutting tool movement to quickly position the tool at a specified location.
G01 – Linear Interpolation: G01 commands linear movement, allowing the tool to move in a straight line from the current position to a designated point at a defined feed rate.
G02 – Circular Interpolation (Clockwise): G02 instructs the machine to move in a clockwise circular path, typically used for creating arcs and curves.
G03 – Circular Interpolation (Counterclockwise): G03 is similar to G02 but directs the machine to move in a counterclockwise circular path.

Coordinate System and Units Selection G-Codes

G10 – Coordinate System Setting: G10 is used to set parameters for coordinate systems, such as tool offsets and workpiece fixture offsets.

Plane Selecting G-Codes

G17 – Select XY Plane: Select the XY plane as the working plane.
G18 – Select XZ Plane: Select the XZ plane as the working plane.
G19 – Select YZ Plane: Select the YZ plane as the working plane.

Unit Selecting G-Codes

G20 – Inch Units Mode: G20 sets the machine to operate in inches, converting all subsequent dimensions to inches.
G21 – Millimeter Units Mode: G21 sets the machine to operate in millimeters, converting all dimensions to millimeters.

Tool and Workpiece Compensation Commands

G40 – Cutter Compensation Off: G40 deactivates cutter compensation, ensuring the tool follows the programmed path without offset.
G41 – Cutter Compensation Left: G41 activates cutter compensation to the left of the programmed path, used for creating toolpaths with a specific offset.
G42 – Cutter Compensation Right: G42 activates cutter compensation to the right of the programmed path, used for creating toolpaths with an offset in the opposite direction.
G43 – Tool Length Compensation Positive: G43 specifies tool length compensation in the positive direction, accounting for tool length variations.
G44 – Tool Length Compensation Negative: G44 specifies tool length compensation in the negative direction, adjusting for tool length variations.

Feed Rate Codes

G93 – Inverse Time Feed Rate Mode: G93 allows for specifying feed rates based on the inverse of time, useful for operations where feed rates vary over time.
G94 – Units per Minute Mode: G94 specifies that feed rates are given in units per minute, as opposed to per revolution or toolpath length.

Thread and Tapping Codes

G76 – Threading Cycle: G76 is used for threading operations on lathes, specifying thread parameters like pitch and depth.
G84 – Tapping Cycle: G84 initiates a tapping cycle, specifying parameters such as feed rate, depth, and pecking behavior.

Other Common G-Codes

G04 – Dwell: G04 introduces a pause or dwell in the program for a specified time, often used for tool changes or coolant flow.
G28 – Return to Home Position: G28 directs the machine to return to a predefined home position, often used as a reference point.
G30 – Return to Second Home Position: G30 is similar to G28 but instructs the machine to return to a second home position if defined.
G80 – Cancel Canned Cycle: G80 cancels any active canned cycle, returning the machine to normal operation.
G90 – Absolute Positioning: G90 sets the machine to operate in absolute positioning mode, where positions are defined relative to a fixed reference point.
G91 – Incremental Positioning: G91 instructs the machine to operate in incremental positioning mode, where positions are defined relative to the current position.
G98 – Return to Initial Point in Canned Cycle: Return to the initial point of a canned cycle, often after completing drilling or tapping operations.
G99 – Return to R-point in Canned Cycle: Return to the R-point, a reference point of a canned cycle, which may be different from the initial point.
G54-G59 – Work Coordinate System Select: These G-codes choose one of six available work coordinate systems for positioning the tool or workpiece.
G70 – Inch Program Mode: G70 specifies that the program uses inches for all dimensions and positions.
G71 – Metric Program Mode: G71 specifies that the program uses millimeters for all dimensions and positions.

M-Code Commands in CNC Programming

The following are the general M-Code Commands. There are some other commands which are specified for particular machines. Always recommend reading the machine manual before using a CNC machine.

Common M-Code Commands

M00 – Program Stop: This code halts the CNC program
M01 – Optional Program Stop: Similar to M00, but it allows for an optional stop, meaning the operator can choose to stop the program or continue.
M02 – Program End: This code signifies the end of the program and prompts the operator to restart the program.
M03 – Spindle On, Clockwise (CW): M03 starts the spindle rotation in a clockwise direction. It is often followed by an S-code to specify the spindle speed.
M04 – Spindle On, Counterclockwise (CCW): M04 starts the spindle rotation in a counterclockwise direction. Like M03, it is followed by an S-code.
M05 – Spindle Stop: M05 stops the spindle from rotating.
M06 – Tool Change: Automatic or manual tool change. It prompts the machine to change to the next tool in the tool magazine.
M07 – Coolant On (Mist): M07 turns on the coolant or mist system for cutting fluid.
M08 – Coolant On (Flood): M08 activates the flood coolant system, which provides a continuous flow of coolant during machining.
M09 – Coolant Off: M09 turns off the coolant systems.
M10 – Pallet Clamp (Pallet Change): Clamp or unclamp pallets on a machining center.

Other M-Codes

M30 – Program End and Rewind: M30 signifies the end of the program and instructs the machine to rewind the program for the next run.
M98 and M99 – Subprogram Calls: Call and return from subprograms. The purpose of M98 is to call a subprogram, while M99 returns to the main program.
M41, M42 – Gear Shift (Lathe): These codes control the gearshift for lathes that have multiple gear ranges.
M80, M81 – Auxiliary Functions: These codes are for various auxiliary functions, such as turning on auxiliary devices like lights, clamps, or chucks.
M90 – Absolute Programming: M90 switches the CNC machine to absolute programming mode, which means that positions are defined with respect to a fixed reference point.
M91 – Incremental Programming: M91 switches the machine to incremental programming mode, where positions are defined relative to the current position.

S-Code, F-Code, and T-Code in CNC Programming

The specific S-codes, F-codes, and T-codes used can vary depending on the CNC machine, and control system.

S-codes (spindle speed codes)

The purpose of the S-codes is to control the rotational speed of the machine tool’s spindle. The spindle speed determines how fast the cutting tool rotates. Which is vital for achieving optimal cutting conditions depending on the material and machining operation.

For example, an S-code like S1000 would set the spindle speed to 1000 RPM (revolutions per minute).

F-codes (feed rate codes)

The purpose of the F-codes is to control the rate at which the cutting tool moves along the workpiece during a machining operation. The feed rate determines how fast the tool advances or retracts, directly impacting the material removal rate and the quality of the machined surface.

For instance, an F-code like F200 would set the feed rate to 200 units per minute. 3.

T-codes (tool selection codes)

The purpose of the T-codes is to specify the tool for a particular machining operation. CNC machines often have multiple tool stations or tool holders, and T-codes help select the appropriate tool.

For example, a T-code like T03 would select tool number 3 from the available tool library.

These codes, along with G-codes and M-codes, provide a comprehensive set of instructions to program CNC machines accurately. By leveraging these codes effectively and understanding their functionalities, CNC programmers can create precise and efficient machining programs to produce high-quality parts.

What is CNC Programming?

What is CNC Programming?