What is a Post Processor?

July 2, 2026
4:26 pm

What is a Post Processor? Post Processor is a software module that converts the toolpath generated in CAM into code that the CNC controller can understand. It acts as a “translator” between design/programming software and the CNC machine. If the wrong post is selected, the program may not run, or it could cause incorrect axis movements, tool collisions, part damage, or machine failure.

What is a Post Processor and Its Role in CNC Machines?
Differences Between CAM, G-code, and Post Processor
What Does Post Processor Output Look Like?
Key Functions of Post Processor
Post Processor Applications in Different CNC Machines
Why a Custom Post Processor is Better?
Difference Between Post Processor and CNC Controller
Important Checks Before Running the Output File
Conclusion

What is a Post Processor and Its Role in CNC Machines?

CAM software such as Mastercam, PowerMill, Fusion 360, SolidCAM, ArtCAM, VCarve, Aspire calculates toolpaths based on part model, tools, material type, spindle speed, depth of cut, and machining strategy. However, this toolpath cannot be directly used by all controllers. Post Processor converts it into the final NC / G-code file.

Process Chain:

Part design in CAD
Toolpath generation in CAM
Post Processor
NC / G-code file
CNC controller
Axis movement and machining operation execution

Differences Between CAM, G-code, and Post Processor

Concept	Definition	Function
CAD	Computer-Aided Design	Part modeling and technical drawing
CAM	Computer-Aided Manufacturing	Toolpath generation and machining strategy
Post Processor	Translator module in CAM	Converting toolpath to machine-specific code
G-code / NC Code	Standard CNC programming language	Final executable program
CNC Controller	Hardware control unit	Reading program and controlling motors, spindle, tools, I/O

Why Do We Need a Post Processor?

Each CNC machine has different hardware and control characteristics:

CNC controller type
G and M command structure
Method of defining zero point
Axis movement directions
Measurement units (millimeters or inches)
Spindle type and on/off commands
Presence or absence of inverter
Manual or automatic tool change
Tool changer type (linear, umbrella, rotary)
Presence of fourth or fifth axis
Table type (fixed, rotary, gantry, tilt)
Presence of vacuum, coolant, mist spray, or compressed air
Operation type (milling, turning, plasma, laser, waterjet, wood, glass, engraving)

What Does Post Processor Output Look Like?

Post Processor output is a text file with extensions like .nc, .tap, .txt, .cnc, .iso, .ncp.

Sample G-code:

gcode

G90 G21
G17
G0 X0 Y0 Z10
M3 S18000
G1 Z-2 F300
G1 X100 Y0 F1200
G1 X100 Y50
G1 X0 Y50
G1 X0 Y0
G0 Z10
M5
M30

Command Meanings:

G90 = Movement based on absolute coordinates
G21 = Millimeter unit
G0 = Rapid movement without cutting
G1 = Linear movement at specified speed
X Y Z = Axis coordinates
F = Tool feed rate
S = Spindle RPM
M3 = Spindle on clockwise
M5 = Spindle off
M30 = End of program and reset

Key Functions of Post Processor

1. Converting Toolpath to Axis Movement

Post Processor can output arc commands G2/G3, linear movements G1, or controller-specific commands.

2. Defining Zero Point and Part Coordinates

Examples:

Lower-left corner
Part center
Hole center
Material top surface
Material bottom surface
Point on fixture

3. Managing Spindle On/Off

Controls spindle RPM, rotation direction, spin-up delay, and inverter control.

Example: M3 S12000 and G4 P2

4. Tool Management and Tool Change

For machines with ATC, commands like T3 M6 are used.

Real steps:

Z moves to safe height
Move to tool changer
Release previous tool
Grab new tool
Check tool sensor
Measure tool length
Return to machining position

5. Controlling Machine Peripherals

Coolant pump
Mist spray
Compressed air
Vacuum
Pneumatic clamps
Holding jacks
Tool measurement and zero-setting systems
Laser marker
Plasma torch
THC (Torch Height Control)
Glass cutting head
Wood engraving/cutting head

For Plasma:

Move to start point
Lower torch
Touch plate
Set initial height
Arc on
Wait for arc formation
Start cutting
THC control
Torch off at end

Post Processor Applications in Different CNC Machines

CNC Mill

Face milling, drilling, tapping, slotting, profile milling
3D machining, engraving, mold part machining
Cutting aluminum, steel, brass, plastic, and wood

CNC Lathe

Facing, diameter turning, threading, grooving
Axial drilling, part cutoff
Three-jaw or collet control

Wood & MDF CNC

MDF cutting, grooving, hinge drilling
Cabinet making, wood engraving
Cabinet door production, decorative parts
PVC, plexiglass, and composite cutting
Emphasis on vacuum importance

Plasma CNC

Torch on/off control
Piercing delay
Cut height start
THC control
Arc activation
Arc OK input
THC off in corners/small holes
Safe height management

Laser CNC

Laser on/off
Laser power adjustment
Movement speed
Pause for piercing, cutting, or engraving
Power adjustment in corners
Inner/outer path management

5-Axis CNC

Due to rotary axes A/B/C in addition to X/Y/Z, Post Processor role is critical:

Kinematic management
Axis angle limitations
Preventing tool and head collisions
Converting tool angle to actual coordinates
Axis control
Table or head positioning
Preventing end-of-travel limits

Using a generic post on 5-axis machines is dangerous. Machine-specific posts must be used.

Why a Custom Post Processor is Better?

Generic CAM posts are not ideal for all machines. A custom post is configured based on actual machine specifications:

CNC controller model
Number and type of axes
Axis directions
Travel range
Tool changer system
Spindle type
Inverter type
Tool change method
Tool sensor presence
Input/output types
Custom M codes
Plasma, laser, or coolant systems
Home and Machine Zero definition
Mechanical limitations

Advantages of Custom Post:

Reduced program execution errors
Reduced operator time
No manual code editing needed
Increased machine safety
Reduced tool collision probability
More accurate CAM path execution
Improved final part quality
Better use of machine capabilities

Difference Between Post Processor and CNC Controller

Aspect	Post Processor	CNC Controller
Location	CAM software	Installed on machine
Function	Converts toolpath to G-code	Executes G-code
Activation time	Before file transfer	During program execution
Dependency	Machine and controller type	Motor, I/O, and safety control

Signs of Inappropriate Post Processor:

Machine moving in wrong direction
Z going down instead of up
Spindle not turning on
Wrong spindle RPM
Vacuum/coolant/air not activating
Tool not moving at safe height
Wrong zero point
Tool change errors
Broken or incorrect circular path execution
Abnormal feed rate
Machine going to wrong position at end
Improper THC activation in plasma
Controller displaying code errors

Important Checks Before Running the Output File

10 Pre-Run Actions:

Check controller model and post processor
Verify file unit (millimeters or inches)
Define part zero and machine zero
Check safe Z height
Verify spindle speed and feed rate
Match tool numbers with actual tools
Review program in CAM simulation
Initial test with low speed or Dry Run
Tool-less or dry run for critical parts
Keep backup of post processor and machine settings

Conclusion

Post Processor is a key component of the CNC process that converts CAM toolpaths into executable programs for the controller. Without a proper post, execution errors, part quality loss, or machine damage can occur.

In 3-axis machines, Post Processor converts toolpaths to motion codes and spindle commands.
In advanced machines like 5-axis, plasma, laser, ATC, and multi-head machines, Post Processor also manages a significant part of the machine’s operational logic.
Proper selection and configuration of Post Processor must align with controller type, mechanical structure, peripherals, and manufacturing process.

“Post Processor generates the program; the controller executes it.”

View Technical Specifications