Machinery's Handbook, 31st Edition
802 CALIBRATION OF VERNIER, DIAL AND DIGITAL CALIPERS a) Alternately the vernier scale can be adjusted to directly compensate for and deviation from nominal dimension of the nib. This can be accomplished by adjusting the inside measurement vernier scale to zero on a known standard. Measurement of the nib nominal dimension must still be performed as excessive wear to the nib will result in adjustment in excess of the available range of the vernier scale. b) Assemble a 1.000 inch gage block with accessory end blocks as shown in Fig. 30 of the Calibration of Inside Dimension Jaws (Nibs) section. c) Measure the gage block stack and adjust the vernier scale to zero at this known point. d) This method is applied to the Type 1 style caliper only.
Inside
1
5
Inside – 0.003 inch
Nominal 0.500 inch Reading 0.467 inch Nib Dimension - Measured with Precision Micrometer
Fig. 28. Nib Dimension Measurement Location Calibration of Jaw Parallelism.— 1) Slide jaws together and tighten the sliding jaw lock screw. Hold the UUT in front of a strong light source. Observe that no light is visible between the jaw measuring surfaces. Look carefully for evidence of burrs, damage to the measuring surfaces, excessive wear or bowing. a) If any burrs or damage appears gently stone the jaws with a white hard Arkansas stone. Only use a super fine grain stone for this operation. 2) Loosen the sliding jaw lock screw and open the jaws. Place the precision cylindrical plug gage or ball in between the jaws as close as possible to the beam and measure the stan dard. Observe the scale, dial, or digital reading. 3) Move the plug gage or ball to the opposite end of the measuring jaws (tip) and remea sure. The difference between the two readings must be within tolerance stated in Table 20. Range and Tolerance Limits for “Outside Jaws”. 4) If the readings are within tolerance, proceed to Calibration of Outside Jaws. If adjust ment is needed, go to Items 5) through 7), in Adjustment of Gib Slide Set Screws . Adjustment of Gib Slide Set Screws.— 5) Using a small precision screwdriver loosen the gib slide set screws then retighten evenly with a slight pressure. a) It is important that both set screws are tightened evenly and a slight resistance is felt in the sliding jaw full range movement. 6) Operate the UUT several times over its full range to ensure that the sliding jaw can be moved smoothly over the full length of the beam.
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