Machinery's Handbook, 31st Edition
CALIBRATION OF VERNIER, DIAL AND DIGITAL CALIPERS 803 7) Repeat steps 1 through 3 to verify the Jaw Parallelism in within tolerance as stated in Table 2 for Outside Jaws. 8) If the readings are within tolerance, proceed to Calibration of Outside Jaws . If read ings are not within tolerance, record all readings as “As Found” and consult the end user to determine the course of action that they desire. Excessive damage or wear to the Jaws, Nibs or ID measuring contacts can result in a high degree of uncertainty in all measurements taken with the instrument and is cause for concern. Consideration of these facts should be addressed before proceeding. Calibration of Outside Jaws.— 1) Slide the UUT jaws together and tighten the sliding jaw set screw. 2) Set zero for this calibration measurement. a) For vernier calipers close the jaws and observe the alignment of the zero indica tion on the main scale and vernier scale. b) For dial calipers, adjust the bezel for proper zero indication. c) For digital calipers, press the ZERO set button on the face of the UUT. Verify the digital indication is between - 0.0005 and +0.0005. 3) Loosen the sliding jaw lock screw. Open and close the sliding jaw to verify repeatabil ity of the zero setting. a) For digital calipers, loosen the jaw set screw and open the calipers to a mid-point location. Lock the jaw set screw then press the zero set switch on the front of the instrument. Verify the digital indication is between -0.0005 and +0.0005. Close the slide jaw and zero the instrument. 4) Select the gage blocks needed to check the caliper at the test points listed below: a) For dial calipers, select the proper gage blocks to check the caliper at the 3 o’clock, 6 o’clock, 9 o’clock and 12 o’clock positions of the dial face in the first inch. (0.125, 0.550, 0.675, 1.000) b) For digital and vernier calipers, select gage blocks equal to 25, 50, 75, 100 percent of the first inch (0.250, 0.500, 0.750 and 1.000 inches). 5) Select the gage blocks needed to check the UUT at 25, 50, 75, and 100 percent of full scale.Place the UUT and all gage blocks on the surface plate for a minimum of 15 minutes to stabilize. The gage blocks should have both working surfaces exposed, as in Fig. 29.
0
90 10
70 80
20 30
60
40
50
Outside Jaws
End Blocks
1.000
4.000
2.000
3.000
Surface Plate
Fig. 29. Gage Blocks and End Blocks Staged for Calibration of 6-inch Dial Caliper
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