How to Do First Article Inspection in CNC Programming

To perform first article inspection in CNC programming, run the initial CNC program on a test part, then measure critical dimensions using precision tools. Compare these measurements against the design specifications and adjust the CNC program as needed before full production.

Syntax

First article inspection in CNC programming involves these key steps:

• Run initial program: Execute the CNC code on a test piece.
• Measure dimensions: Use tools like calipers or CMM to check critical features.
• Compare to specs: Verify measurements against the design drawing.
• Adjust program: Modify CNC code if dimensions are off.
• Repeat inspection: Confirm corrections by re-running and measuring.

gcode

N10 G21 (Set units to mm)
N20 G90 (Absolute positioning)
N30 M06 T01 (Tool change to tool 1)
N40 G00 X0 Y0 Z5 (Rapid move to start)
N50 G01 Z-5 F100 (Cutting feed)
N60 X50 Y0 F200 (Cutting move)
N70 X50 Y50 (Cutting move)
N80 X0 Y50 (Cutting move)
N90 X0 Y0 (Cutting move)
N100 G00 Z5 (Retract)
N110 M30 (End program)

Example

This example shows a simple CNC program for milling a square. After running this program on a test piece, measure the square's sides with a caliper. If the sides are not exactly 50 mm, adjust the X and Y coordinates in the program accordingly.

gcode

N10 G21
N20 G90
N30 M06 T01
N40 G00 X0 Y0 Z5
N50 G01 Z-5 F100
N60 X50 Y0 F200
N70 X50 Y50
N80 X0 Y50
N90 X0 Y0
N100 G00 Z5
N110 M30

Output

The CNC machine mills a 50x50 mm square pocket on the test material.

Common Pitfalls

• Skipping measurement: Not measuring the first part can lead to mass production of faulty parts.
• Ignoring tool wear: Using worn tools during inspection can give inaccurate results.
• Not documenting changes: Failing to record program adjustments causes confusion later.
• Rushing inspection: Hurrying can miss small but critical errors.

Always use calibrated measuring tools and take your time to ensure accuracy.

gcode

;; Wrong: Running program without measuring
N10 G21
N20 G90
N30 M06 T01
N40 G00 X0 Y0 Z5
N50 G01 Z-5 F100
N60 X50 Y0 F200
N70 X50 Y50
N80 X0 Y50
N90 X0 Y0
N100 G00 Z5
N110 M30

;; Right: Run program, measure, then adjust
;; Measure sides with caliper
;; If side is 49.8 mm, increase X and Y moves by 0.2 mm
N60 X50.2 Y0 F200
N70 X50.2 Y50.2
N80 X0 Y50.2
N90 X0 Y0

Quick Reference

• Run initial CNC program on test piece.
• Measure critical dimensions precisely.
• Compare measurements to design specs.
• Adjust CNC code to correct errors.
• Repeat inspection until parts meet quality.

Key Takeaways

Always run the CNC program on a test part before full production.

Use precise measuring tools to check critical dimensions.

Compare measurements carefully against design specifications.

Adjust the CNC program based on inspection results.

Document all changes and repeat inspection to ensure quality.