131.3.4 - CAD/CAM/CNC Mills

CNC Mill G-Code Post-Processing

CNC Milling Setup Sheets

Setup sheets are an essential aspect of CNC machining. They serve as a critical tool for standardizing and documenting the setup process, which is essential for consistency and repeatability in manufacturing. Setup sheets serve as a comprehensive guide that outlines all the necessary steps, tools, and offsets required to set up a specific job. They help reduce errors, save set up time, and ensure a consistent, robust process with predictable results.

Components of a Setup Sheet:

Job information: Part name, number, and revision.
Workpiece details: Material, size, and orientation.
Tooling information: Tool numbers, details, and operations.
Workholding details: Type of fixture, clamping methods, and positions.
Work Coordinate Offsets: Workpiece origins and work coordinate systems (WCS, i.e. G54).
Special notes or instructions: Any unique considerations or precautions for the specific job.

Creating a Set-up Sheet

Most CAM programs offer a function to generate a setup sheet from the information provided to develop the CNC program. These pre-made setup sheets may be overly complex and provide more information than needed. You may want to consider developing your own setup sheet template or finding one.

Post-Processing for CNC Mills

Post processors are programs that convert toolpaths created by CAM software into a program that a CNC machine can read and understand. Most CAM software comes pre-equipped with a post-processors or you can find a stand-alone post-processing program. You can even create or edit your own post processor. Regardless of type of post processor utilized there are some import considerations to keep in mind.

Post processing Considerations:

Select the correct machine/control - Most post processors are equipped with a library of machine tools and controls. Ensure you select the correct machine and control model in your post processor. G- and M-codes vary between machine makes, models, and controls. For example, the Haas Mini and TM mills in our shop have pre-NGC controls where the ST lathes have NGC controls.
Safety Line after each operation - A good practice to develop is to place a safety line after each tool change. This creates a standard machinig enviroment for all tools to start from. This is especially helpful and safer when having to re-run an operation.
- Safety Line Example: G54 G90 G0 G17 G40 G49 G80 G20
  - G54: Work Coordinate System (WCS), G54-G59
  - G90: Absolute positioning
  - G0: Rapid movement
  - G17: XY plane
  - G40: Cutter compensation cancel
  - G49: Tool length offset cancel
  - G80: Canned cycle cancel
  - G20: Imperial units of measurement (inches)
Clear external/common offsets - Common or external offsets are used to shift the WCS with out altering the initial offset. Common offsets effect all WCS's, not just an individual WCS. Clearing the common offsets at the beginning and end of a program is a good safeguard to prevent any unplanned WCS shifts.
Review the program before running it - You never want to run a program without reviewing the code. Visual Studio Code is a good program to view and edit your program before taking it to a machine. When reviewing the program, check for correct feeds/speeds, tool changes, as well as work and cutter offset activation.

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4.4✔ CHECKPOINT

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