G-CODE Book: The Essential Resource for CNC Machinists

Lathe Axes For a Typical CNC Turning Center

5 Axes Mill with Trunion Table

Mill Axes For a Typical Vertical Machining Center

EXPRESSING COORDINATES IN G-CODE

In G-code, coordinates are typically expressed using absolute or relative positioning depending on the command. How coordinates are expressed:

Absolute Coordinates

Absolute coordinates specify the exact position relative to the machine's reference point.

For example, to move to a point where:

• X coordinate is 100,
• Y coordinate is 50,
• Z coordinate is 10,

G01 X100 Y50 Z10

Relative Or Incremental Coordinates

Relative coordinates specify movement relative to the current position.

For example, to move 10 units in the X-axis, 5 units in the Y-axis, and -2 units in the Z-axis from the current position, y

G01 X10 Y5 Z-2

Incremental and Absolute Modes

• Incremental mode: Coordinates are relative to the current position.
• Absolute mode: Coordinates are absolute from the machine's origin.

The mode can be set using G90 (absolute mode) or G91 (incremental mode).

Tips

• Always ensure your G-code program starts with setting the appropriate mode (G90 for absolute, G91 for incremental) to avoid unexpected behavior.
• Check the documentation for your specific CNC machine can vary slightly between different implementations of G-code.

WHAT ABOUT UNITS—METRIC OR IMPERIAL?

In G-code, the choice between metric (mm) and imperial (inches) units depends on the machine's configuration and the G-code program.

Metric Units (mm)

G20 Mode: Metric units are typically denoted in millimeters (mm).

Example: G21 Set units to millimeters (metric)
G01 X50 Y30 Z5
Move to absolute position X=50mm, Y=30mm, Z=5mm

Imperial Units (Inches)

G21 Mode: Imperial units are denoted in inches.

Example: G20 ; Set units to inches (imperial)
G01 X2.0 Y1.5 Z0.25
Move to absolute position X=2.0 inches, Y=1.5 inches, Z=0.25 inches

TOOL OFFSET

In manufacturing and machining contexts, "tool offset" refers to a crucial parameter used in CNC machining operations.

Tool Offset in CNC Machining:

• 1. Definition: Tool offset refers to the deviation or difference in dimensions between the theoretical position of a cutting tool and its actual position when mounted in the machine spindle. This discrepancy can arise due to various factors such as tool wear, tool length variations, or calibration inaccuracies.
• 2. Setting Tool Offsets: Operators typically set tool offsets through the machine’s control panel or software interface. This involves measuring the tool dimensions accurately using specialized tools or gauges and inputting these dimensions into the machine’s memory.

For X axis Offset –

Hold workpiece in spindle & touch Tool to OD.By Vernier measure diameter of the workpiece, for example 30 mm.Then , go to Tool offset, take cursor to as per “X”tool number , then press X30.0 “Measure”.

PROGRAM BLOCK -

CNC MILLING G-CODE REFERANCES –

CNC MILLING M-CODE REFERANCES –