Complete CNC Machining Center Program Code Reference – A Must-Have for CNC Machining

1. Meaning of Letters in CNC Programs

O: Program number – sets the program number
N: Block number – sets the program sequence number
G: Preparatory function code
X / Y / Z: Dimensional characters – axis movement commands
A / B / C / U / V / W: Additional axis movement commands
R: Arc radius
I / J / K: Arc center coordinates (vector values)
F: Feed rate – sets the feed speed
S: Spindle speed – sets the spindle rotation speed
T: Tool function – sets the tool number
M: Miscellaneous function – on/off control functions
H / D: Tool offset number – sets the tool offset
P / X: Dwell time – sets the delay time
P: Subprogram number command – sets subprogram numbers (e.g., subprogram call: M98 P1000)
L: Repeat count – sets the number of repetitions for a subprogram or fixed cycle (e.g., M98 P1000 L2; omitting L means L1)
P / W / R / Q: Parameters – used in fixed cycles (e.g., tapping cycle G98/(G99) G84 X_ Y_ R_ Z_ P_ F_)

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2. Common G-Code Explanations

G00: Rapid positioning
G01: Linear interpolation
G02: Circular/helical interpolation (clockwise)
G03: Circular/helical interpolation (counterclockwise)
G04: Dwell or delay time
Example: G04 X1000 or G04 X1.0
G04 P1000 means a 1-second dwell

G09: Exact stop check (verifies the tool is within the target range)
G10: Programmable data input
G17: Select XY plane (X axis or its parallel axis)
G18: Select ZX plane (Y axis or its parallel axis)
G19: Select YZ plane (Z axis or its parallel axis)
G20: Inch input mode
G21: Metric input mode

G28: Return to reference point
Format: G91/(G90) G28 X__ Y__ Z__ – returns via an intermediate point to the reference position (absolute/incremental mode)

G29: Return from reference point
G91/(G90) G29 X__ Y__ Z__ – from the start point, pass the reference point and return to the target position

G30: Return to 2nd, 3rd, or 4th reference point
Example:
G91/(G90) G30 P2 X__ Y__ Z__ – return to the 2nd reference point (P2 can be omitted)

G40: Cancel cutter radius compensation
G41: Cutter radius compensation left (tool to the left in feed direction)
G42: Cutter radius compensation right (tool to the right in feed direction)
G43: Tool length compensation + direction
G44: Tool length compensation − direction
G49: Cancel tool length compensation

G50: Cancel scaling
G51: Scaling – format:
ON: G51 X_ Y_ Z_ P_
OFF: G50
Where X/Y/Z set the scaling center and P is the scaling factor (1–999999, integers only; P800 means 0.8 scaling)

G52: Set local coordinate system
G53: Select machine coordinate system
G54–G59: Select work coordinate systems 1–6

G60: Single-direction positioning – eliminates backlash
G61: Exact stop check – decelerates and checks tolerance near the target position
G62: Automatic cornering feed rate adjustment
G63: Tapping cycle
G64: Normal cutting mode – no deceleration between segments

G65: Macro call
G66: Modal macro call
G67: Cancel modal macro call

G68: Coordinate rotation – format:

• G17: G68 X_ Y_ R_
• G18: G68 X_ Z_ R_
• G19: G68 Y_ Z_ R_

G69: Cancel coordinate rotation

G73: Peck drilling cycle
G74: Left-hand tapping cycle
G76: Fine boring cycle (with oriented retraction)
G80: Cancel fixed cycle
G81: Simple drilling cycle
G82: Drilling cycle with dwell at the bottom
G83: Peck drilling cycle
G84: Right-hand tapping cycle
G85–G89: Boring cycles (various types)

G90: Absolute programming
G91: Incremental programming
G92: Set work coordinate system
G98: Return to initial point in fixed cycle retract
G99: Return to R-point in fixed cycle retract

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3. Common M-Code Explanations

M00: Unconditional program stop
M01: Optional program stop
M02: End of program
M03: Spindle on clockwise
M04: Spindle on counterclockwise
M05: Spindle stop
M08: Coolant on (external)
M09: Coolant off (all)
M26: Coolant on (internal)
M30: End of program and return to start

M84: Check pallet 1
M95: Check pallet 2
M98: Call subprogram
M99: Return to main program
M135: Rigid tapping
M417: Machine pallet 1 check
M418: Machine pallet 2 check
M419: End pallet check
M433: Tool breakage detection
M462: Transfer pallet number

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4. Common Arithmetic in CNC Programming

Addition: #i = #j + #k
Subtraction: #i = #j - #k
Multiplication: #i = #j * #k
Division: #i = #j / #k

Sine: #i = SIN[#j]
Arcsine: #i = ASIN[#j]
Cosine: #i = COS[#j]
Arccosine: #i = ACOS[#j]
Tangent: #i = TAN[#j]
Arctangent: #i = ATAN[#j]

Square root: #i = SQRT[#j]
Absolute value: #i = ABS[#j]
Round: #i = ROUND[#j]
Round down: #i = FIX[#j]
Round up: #i = FUP[#j]
Natural log: #i = LN[#j]
Exponential: #i = EXP[#j]

Logical OR: #i = #j OR #k
Logical XOR: #i = #j XOR #k
Logical AND: #i = #j AND #k

BCD to Binary: #i = BIN[#j]
Binary to BCD: #i = BCD[#j]

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5. Logical Operators

EQ: Equal to
NE: Not equal to
GT: Greater than
GE: Greater than or equal to
LT: Less than

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6. Program Branching and Loops

Unconditional jump: GOTO
Conditional jump: IF [condition]
Example:
IF [condition] GOTO n – if the condition is met, jump to block n
IF [condition] THEN – e.g., IF [#I EQ #J] THEN #K = 0

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7. Loop Statements

WHILE [condition] DO m    (m = 1, 2, 3…)
    ...
ENDm

If the condition is true, the program between DOm and ENDm is executed repeatedly until the condition becomes false. Otherwise, execution continues after ENDm.

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If you want, I can also reformat this into a professionally designed CNC programming quick reference table so it’s easier to read and print for workshop use. That would make it look like a real machinist’s handbook page.