Machinery's Handbook, 31st Edition
804 CALIBRATION OF VERNIER, DIAL AND DIGITAL CALIPERS 6) Open the outside jaws and measure the gage block that equates to the first test point defined in step 4. Ensure that the jaws are squarely placed with a slight pressure against the gage block measuring surfaces. Use the thumb wheel or fine adjust to apply gentle but steady pressure against the gage block. Rock the caliper gently to ensure that the OD measuring faces are seated squarely. Seek the smallest reading obtainable with gentle pressure. Record the value. 7) Repeat Item 6) for remaining test points defined in Item 4), parts a) and b), and Item 5). 8) If the outside jaws are within tolerance, proceed to the next section: Calibration of Inside Dimension Jaws (Nibs) . If the outside jaws are found Out of Tolerance, continue through each calibration section and record all data as “As Found” prior to any further adjustments. Upon completion of procedure, report any out of tolerance conditions that may have been discovered. Any out of tolerance conditions must be addressed before returning the UUT to service. Calibration of Inside Dimension Jaws (Nibs).— 1) Select the gage block needed to check the UUT at the first test point as defined above in Item 4) of Calibration of Outside Jaws . Clean the surface of the gage block and end blocks with lint free wipe and alcohol and assemble the Accessory End Blocks and assure they are secured in position snugly. 2) Close the caliper jaws and assure the dial or digital indication or vernier scale indicate zero. 3) Measure the dimension of the gage block as illustrated in Fig. 30. Use a gentle rocking motion to assure that the jaws are seated squarely. Seek the lowest reading as this is the true distance between the parallel faces of the end blocks. Note: Excessive force must be avoided as this can cause deformation of the UUT jaws and result in erroneous readings. A gentle consistent feel must be used to provide an accu rate reading. If too much force is applied or the ID measuring jaws are not in line and perpendicular to the parallel planes of the end blocks, a larger and unrepeatable reading will result. Repeat all measurements several times to assure that you have a true reading.
1.000
4.000
End Blocks
2.000
3.000
Surface Plate
Fig. 30. Inside Dimension Measurement of Gage Blocks using Accessory End Blocks 4) Repeat the set up and readings at the 3 o’clock, 6 o’clock, 9 o’clock and 12 o’clock positions of the dial face in the first inch. For vernier and digital calipers measure at 0.250, 0.500, 0.750 and 1.000 inches. Record all readings.
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