Quality Magazine

Training Trends:<br>Calibrate CMMs

May 19, 2003
While browsing several manufacturing reader forums, one question keeps getting repeated. The wording may vary, but the sentiment remains the same:

How do I calibrate XXXXX? Fill in the blank with any number of gages and equipment. Vantek Corp. (North Tonawanda, NY) has compiled a list of calibration procedures from various manufacturers and produced a general calibration procedure for coordinate measuring machines (CMMs). The procedure can be modified to fit a company's specific needs.

1. Purpose.

To establish a standard procedure for calibration of a CMM.

2. Scope.

All CMMs measure, gage, test, inspect or examine items to determine compliance with specifications, set specifications or those that are deemed critical to the control of a process.

3. Referenced Documents.

Equipment Calibration Record, ADS Form No. 3.01 (CMM Comparator).

4. Materials Required.

Surgically clean absorbent cotton; lint-free cloth; acetone-type cleaner; calibrated stack master, laser interferometer or digital master gages; force tester; and calibrated square standard.

5. Special Precautions.

Use a quality cleaning solution and lint-free cloth for cleaning the bearing surfaces of the equipment.

6. Tolerances.

Refer to instrument manufacturer specifications for accuracy and precision tolerances. If there is some functional characteristic that requires tolerancing other than that specified above, these considerations should govern the acceptability of the instrument.

7. Procedure.

7.1 Verify that identification markings on the machine are distinct and in agreement with the equipment calibration record.

7.2 Examine CMM for obvious damage or other signs of mishandling or wear that may affect the accuracy or function. Refer to section 8 for remedial action.

7.3 Clean all ways and bearing surfaces. Use lint-free cloth and a few drops of manufacturer's recommended cleaner. Apply minimal pressure when cleaning.

7.4 Clean exposed surface plate areas.

7.5 Clean scales as needed with manufacturer's recommended cleaning solution.

7.6 Check and record machine axis squareness as follows: X to Y, Y to Z and X to Z.

7.7 Input master calibration values and iterations information in appropriate windows in calibration control program.

7.8 Check linear accuracy of each axis with respect to master calibration values, and record measured deviations at each interval in the appropriate input section of the equipment calibration record, ADS Form No. 3.01.

7.8.1 Repeat section 7.8 to correspond with the appropriate number of iterations.

7.8.2 Repeat section 7.7 to 7.8.1 for each axis X, Y and Z.

7.8.3 Measure touch-probe deflection pressure, where applicable, with force tester and record in comment section of calibration report.

7.8.4 Check machine level and record in comment section of calibration report.

7.9 Label machine with calibration sticker.

8. Gage Correction.

If at any time during calibration values exceed accuracy and or precision tolerances, route to a qualified individual for repair or corrections, and recalibrate machine after adjustments have been made.

9. Reference.

Mil-Std 45662, Mil-I-45208A, ISO-9001 or Machine Standard. Curtis Hall is the president of Vantek Corp. He can be reached by phone at (716) 743-0377 or by e-mail at chall@vantek-corp.com.