Cutter radius compensation is a crucial concept in CNC milling that allows the machine to account for the size of the tool’s cutting radius. This ensures that the part is machined accurately according to the dimensions specified in the program, despite the physical size of the cutter.

Usage Format

The G-code commands used for cutter radius compensation are:

• G41: Cutter compensation to the left
• G40: Cancel cutter compensation
• G42: Cutter compensation to the right

Explanation

When a CNC machine follows a programmed path, the center of the tool, not its cutting edges, follows the exact path. Without compensation, the actual cut would be offset by the tool’s radius. G41 and G42 commands tell the machine to adjust the path to compensate for this offset, ensuring the dimensions of the finished product are accurate.

Example

Consider a simple program to mill a square outline on a piece of material:

T0101 (10MM ENDMILL); M06; G21 G90; S800 M03;
G41 P5.0; G00 X0.0 Y0.0; Z-10;
G01 Y60.0 F100.0; X100.0; Y0.0; X0.0;
G00 Z50.0; G40; X200.0 Y200.0;

In this example, G41 P5.0 activates left cutter compensation with a 5mm offset, which is the radius of the 10mm endmill. The toolpath is adjusted so the cutting edge, not the center, follows the intended path.

Text Diagram:

+100.0
|
|   +----------------+
|   |                |
Y60.0 |                |
|   |                |
|   +----------------+
|
+0.0  +0.0            X100.0

The tool starts at the origin (X0.0, Y0.0), moves up to Y60.0, then right to X100.0, down to Y0.0, and back to X0.0 to complete the square. G40 is used at the end to cancel the cutter compensation before moving the tool away from the workpiece.