Mastercam Post Processor Editing File

Mastercam Post Processor Editing: A Guide to Customizing G-Code

In Mastercam, a post processor acts as a translator, converting the generic toolpath data from your CAM software into machine-specific G-code that your CNC controller understands. While Mastercam offers thousands of ready-to-use posts, manual editing is often required to fine-tune machine behavior, automate safety retracts, or integrate custom macro logic. The Core Components of a Mastercam Post

A functional "post" in Mastercam isn't just one file; it is typically comprised of three essential elements:

Machine Definition (.mcam-control): Defines physical machine attributes like travel limits and axis orientation.

Control Definition (.mcam-mmd): Specifies the formatting of the G-code, such as arc support and decimal precision.

PST File (.pst): The primary script file containing the logic and formatting rules for G-code output.

PSB File (.psb): Some custom or advanced posts include an encrypted "binary" file that contains protected logic you cannot edit directly. How to Edit a Post Processor

Editing a post is essentially a scripting task. You can modify these files using any text editor, though many developers use specialized editors like Mastercam Code Expert or CIMCO Edit for syntax highlighting.

Locate the File: Post files are usually found in the C:\Users\Public\Documents\shared Mastercam 20xx\Posts directory.

Backup Your Post: Always create a copy of your .pst file before making changes. One misplaced character can cause machine crashes or output errors. mastercam post processor editing

Open and Search: Open the .pst file in your editor. Most edits involve searching for "post blocks" (sections starting with p) such as: pheader: Controls the very beginning of the G-code program. psof: "Start of file" logic for the first tool change. ptlchg: Logic used for subsequent tool changes. peof: "End of file" commands like parking the machine.

Test and Debug: After saving, post-process a simple toolpath in Mastercam and inspect the G-code to ensure the changes appear as expected. Some advanced users use debugging tools to step through the post logic line-by-line. Common Customizations

Safety Lines: Adding or removing specific G-codes (like G21 for metric or G91 G28 Z0 for homing) at the start of a program.

Coolant Codes: Changing how and when M08 (flood) or M07 (mist) are triggered.

Custom Macros: Integrating advanced automation like tool life management or probing cycles directly into the posted code.

Comments: Formatting how tool names and operation notes appear in the G-code for the operator. Professional Support vs. DIY

While minor edits (like changing a text string) are common for users, complex multi-axis posts (4-axis or 5-axis) often require expert intervention. Many shops work with their Mastercam Reseller to develop custom posts, as errors in complex kinematic logic can lead to expensive machine damage.

For those looking to master this skill, specialized training programs cover Fanuc, Haas, and Siemens logic, teaching users how to build IF/WHILE loops and math-driven cycles into their posts.

This document presents a comprehensive technical deep dive into the architecture, logic, and methodology of editing Mastercam Post Processors. It is structured for CNC programmers, manufacturing engineers, and post processor developers seeking to move beyond basic modifications into structural customization. Mastercam Post Processor Editing: A Guide to Customizing

Part 1: Understanding the Beast – The Mastercam Post File Structure

Before you open a file in a text editor, you must understand what you are looking at. Mastercam posts typically have the .pst or .psb extension.

.PST (Post Text): This is the human-readable text file. You can open it with Notepad++, Sublime Text, or the built-in Mastercam Post Editor.
.PSB (Post Binary): This is a compiled, encrypted section of the post. Machine tool builders often use this to protect proprietary logic. You can edit the .pst, but you cannot see inside the .psb.

Debugging: The MP.DLL and MPMASTER

When your post crashes or outputs garbage G-code, use the MP.DLL Debugger:

In Mastercam, go to Settings > Control Definition > Post Processor.
Enable Debug and Log NCI.
Post your code. The debug window will show you exactly which line of the post logic is failing.

8.2 "Printing" to the NC File

The simplest debugging method is inserting diagnostic prints.

"(" + "Debug: Tool number is " + tool$ + ")"   #Comments in parentheses

Conclusion: The Post is a Living Document

Your post processor is not a static file. It is a living reflection of your machine shop’s standards. Every time you buy a new machine, a new probe (Renishaw), or a new bar feeder, your post will need editing.

Master the basics: understand psof$, ptlchg$, and modal logic. Use a proper editor. Test ruthlessly. And remember—the best post processor is invisible. You click "Post," perfect G-code appears, and the machine runs. No drama. No manual edits. That is the art of post processor editing.

Mastercam post processor editing is the bridge between your digital CAM design and a machine-ready G-code program. While Mastercam provides a vast library of ready-to-run posts, minor customizations can significantly improve machine efficiency, accuracy, and shop-floor productivity. Understanding the Mastercam Post System

A Mastercam "post" isn't just one file; it's a trio that defines how your machine behaves:

Machine Definition (.mcam-mmd): Describes the physical kinematics, such as travel limits and axis configurations.

Control Definition (.mcam-control): Sets controller-specific logic, like how to format arcs (I, J, K vs. R) and drilling cycles. Part 1: Understanding the Beast – The Mastercam

Post Processor (.pst): The actual script that translates Mastercam's internal toolpath data into the specific G-code and M-code your CNC understands. Getting Started with Editing

To begin editing, you need the right tools and a safety-first mindset.

Introduction to Post Processors in Fusion [Update 2025] - Autodesk

Don’t Be a Hero

You don’t need to build a 5-axis, dual-spindle Swiss post from scratch. Even skilled integrators take weeks to do that. Start small:

Edit the program header (pheader$).
Add a safety line (G17 G40 G49 G80).
Modify the file extension (.nc to .eia).

Test, iterate, and document every change with comments (using #).

When you stop blaming the post and start commanding it, you aren’t just a CAM programmer anymore—you’re a machine whisperer.

Have a specific post editing nightmare? Share your error code in the comments below. Chances are, someone has already fixed it with three lines of MP logic.

The “Infinite Incremental” Trap

Symptom: Your Z values keep getting smaller (-1, -2, -3) but should be absolute. Cause: You set absinc (absolute/incremental mode) incorrectly. Find the pset_mach block and ensure absinc$ = 0 for absolute.