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Mastercam Post Processor Editing __link__ May 2026

Mastering the Machine Code: The Ultimate Guide to Mastercam Post Processor Editing

Abstract

The Mastercam Post Processor acts as the translational layer between the proprietary Mastercam NCI (Cutter Location) file and the specific G-code syntax required by a CNC controller (e.g., Fanuc, Siemens, Heidenhain). Unlike simplistic "translators," the Mastercam post processor is a logic-driven program executed by the "MP" (Mastercam Post) engine. This paper explores the structural hierarchy of the .pst file, the mechanics of the NCI-to-G-code conversion, and advanced techniques for debugging and customization.

Scenario 2: Changing Coolant Types

The Problem: Mastercam outputs M8 for mist, but your machine uses M7 for mist. The Fix: Locate the pcool$ post block. It looks something like this:

pcool$      # Coolant output
      if cool_ant$ = 1, result = force$ ("M8"), e$
      if cool_ant$ = 2, result = force$ ("M7"), e$

Simply swap the strings:

  • Change "M8" to "M7"
  • Change "M7" to "M8"

Or, if your machine uses Flood (M8) and Thru-spindle (M88), you change the string entirely: result = force$ ("M88"), e$

Part 3: The Toolchain – How to Open and Find Things

Step 1: Get the right editor. Do not use Notepad (Windows default). Use Notepad++ or VS Code with the "Mastercam Post" language plugin. This provides syntax highlighting, which makes finding variables 100x easier. mastercam post processor editing

Step 2: Locate your post.

  • Default path: C:\Users\Public\Documents\Shared Mastercam 2024\Mill\Posts\ (Version number varies).

Step 3: Understand the "Lookup" logic. Scroll down past the initial copyright text. You will see sections like: Mastering the Machine Code: The Ultimate Guide to

  • # Global Variable declarations
  • # Format assignments
  • # String definitions
  • # Post blocks

The most important area is the Post Blocks. These are the "subroutines" of the post. They start with p (e.g., psof$ for Start Of File, pheader$ for header, pcool$ for coolant, prapid$ for G00, plin$ for G01).

Why Can’t You Just Use the Generic Default Posts?

You can. But generic posts don’t know that: Scenario 2: Changing Coolant Types The Problem: Mastercam

  • Your machine requires an M10 (hydraulic clamp) before rotating the B-axis.
  • Your coolant is a high-pressure through-spindle type (M162 instead of M8).
  • You want an M00 for a part inspection after every eighth operation.
  • Your tool library uses H values that don’t match the tool number.

Editing the post automates these rules so your programmers don’t have to manually edit G-code every single time.