Like most test, measurement and inspection equipment, gage blocks require regular calibration to maintain accuracy. Scratches, gashes and other damage caused by wear and corrosion can negatively affect the blocks' accuracy. Subjecting the gage blocks to calibration is the best way to verify accuracy. The frequency of calibration depends on the tolerance requirements of the job, the amount of use and conditions under which the gage blocks are used. Vantek Corp. (North Tonawanda, NY) has compiled a list of calibration procedures for gage blocks that, when tailored to meet a company's requirements, can be used as part of employee training.

1. Purpose.
To establish a standard procedure for calibration of standard gage block sets.

2. Scope.
All standard gage block sets used to measure, gage, calibrate, test, inspect or otherwise examine items to determine compliance with specifications, set specifications or perform other procedures that have been reviewed and are deemed critical to the control of a process.

3. Responsibility.
The quality assurance manager is responsible for ensuring overall implementation of the procedure.

4. Referenced Documents.
Equipment Calibration Form for Hand Gages, as specified by the individual company's quality manual.

5. Materials Required.
Gage block comparator or appropriate comparator gage; hard Arkansas stone; and degreasing solvent or cleaner.

6. Special Precautions.
Use extreme care when using Arkansas stone so that only the positive surface imperfections on the gaging surfaces are removed.

7. Tolerances.
According to the manufacturer's applied-grade tolerance or company policy.

8. Procedure.
8.1 Gaging surface of block along with contact surfaces of comparator gage shall be cleaned with an appropriate cleaner or solvent so that all shop coatings, dirt, fingerprints and other foreign substances are removed. Handle blocks with gloves or tweezers to avoid temperature change of the block. Set block on heat sink or surface plate to normalize temperature before taking measurements.

8.2 Carefully check gage blocks for mutilation, scratches or other signs of mishandling or wear that might affect accuracy.

8.3 Place the gage block between the contact points and bring it in contact with the member until the member is supported by the pressure of the contact points.

8.4 Measure three points on each block--left, center and right.

8.5 Record the value representing the furthest deviation from the standard on the Equipment Calibration Form for Hand Gages.

8.6 Repeat steps 8.3 to 8.5 a sufficient number of times to correspond with the selected number of iterations.

8.7 The diameter of the block should not exceed the specified limit at any point along the measuring surface. Refer to procedure 7 for specified tolerance.

9. Gage Correction.
Any gage exceeding the specified tolerance listed in procedure 7 at any time during calibration shall be returned for restricted use or scrapped and replaced.

10. Reference.
ISO 9001, 10.2 Mil-Std-45662 and 10.3 Mil-I-45208A.

Curtis Hall is president of Vantek Corp. He can be reached by phone at (716) 743-0377 or by e-mail at [email protected].