Shenzhen Alu Rapid Prototype Precision Co., Ltd.

Checking the accuracy of a CNC (Computer Numerical Control) machine is critical to ensure it produces parts within specified tolerances. Here's a concise guide on how to assess CNC machine accuracy:

1. Understand Accuracy ParametersPositional Accuracy: 

How precisely the machine moves to programmed coordinates.

Repeatability: The machine's ability to return to the same position consistently.

Geometric Accuracy: Straightness, flatness, and squareness of machine axes.

Thermal Stability: How temperature changes affect accuracy.

Cutting Accuracy: Precision of the finished part compared to the design.

2. Preparation

Inspect Machine Condition: Ensure the machine is clean, lubricated, and free of wear or damage (e.g., check spindle, ways, and bearings).

Calibrate Tools and Probes: Verify that cutting tools, tool holders, and probes are in good condition and properly calibrated.

Stabilize Environment: Minimize temperature fluctuations and vibrations in the workspace, as these can affect accuracy.

Check Workholding: Ensure fixtures and vises are secure and properly aligned.

3. Methods to Check Accuracy

a. Test with Precision InstrumentsDial Indicators: Measure deviations in axis movement or spindle runout.

Laser Interferometry: Use a laser system to measure positional accuracy and straightness of axes with high precision.

Ballbar Testing: Perform a ballbar test to evaluate circular interpolation, servo tuning, and geometric errors. This involves attaching a ballbar device to the machine and running a programmed circular path.

CMM (Coordinate Measuring Machine): Use a CMM to measure the dimensions of a machined test part and compare them to the design specifications.

b. Machine a Test PartCreate a test part with known dimensions (e.g., a square, circle, or hole pattern).

Measure the part using precision tools like calipers, micrometers, or a CMM.

Compare measurements to the CAD model or blueprint to assess dimensional accuracy and surface finish.

c. Run Standard Test ProgramsUse industry-standard test programs like NAS 979 (circle-diamond-square test) or ISO 230-4 to evaluate circularity, squareness, and positioning accuracy.

Analyze the results for deviations from expected tolerances.

d. Check BacklashMeasure backlash (play in the machine’s mechanical components) using a dial indicator while moving an axis back and forth.

Excessive backlash indicates worn components or improper calibration.

e. Thermal Drift TestRun the machine for an extended period to warm it up, then measure positional accuracy at different intervals to check for thermal expansion effects.

4. Analyze Results

Compare measurements to the machine’s specifications or tolerances required for your application.

Identify patterns in errors (e.g., consistent deviation in one axis may indicate misalignment or wear).

5. Adjust and Recalibrate

Compensate Errors: Use the machine’s control software to adjust for detected errors (e.g., backlash compensation or axis calibration).

Maintenance: Address mechanical issues like worn bearings, loose belts, or misaligned guides.

Recheck: Repeat tests after adjustments to confirm improvements.

6. Document and Monitor

Record test results, including measurements and conditions, for future reference.

Schedule regular accuracy checks as part of preventive maintenance.