Machinery's Handbook, 31st Edition
796 CALIBRATION OF THREAD MICROMETERS dedicated to a range of thread pitch. Most sets also include a set of flat anvil and spindle inserts that can be used to calibrate the micrometer exactly the same as a standard mi-
crometer. If this is the case proceed as follows. 2) Select the flat anvil and spindle set and install. 3) Zero the anvil and spindle and assure repeatability.
4) Perform calibration as described in Linearity Test (Outside Micrometers) , Item 3) on page 792 using the defined test points to verify the accuracy of the micrometer head. 5) Remove the flat anvil and spindle set and install the smallest (highest pitch) dedicated Anvil V and Spindle Cone set. Close anvil and spindle and re zero the micrometer to the new set. 6) Select one master thread setting plug gage for the pitch range, preferably at midrange of travel, and measure as described in Linearity Calibration (Fixed Pitch) section. Verify that the measurement is within the tolerance limits of the UUT. This measurement verified the accuracy of the flank angle of the cone and V anvil. This measurement can also be performed on an optical comparator. However, the physical measurement should be performed as the final step in the calibration of the interchangeable cone and anvil sets. 7) Repeat for all remaining Anvil V and Spindle Cone sets. Calibration of Inside Micrometers Caliper Type Inside Micrometer.— A description of the calibration and equipment re- quirements for the Type II, Class 1, Inside Micrometer with Jaws are given in Table 15. Table 15. Calibration Requirements of the Type II, Class 1, Inside Micrometer with Jaws Calibration Description UUT Characteristics Performance Specifications Test Method
Range: 0.200 to 1.000 inch 0.500 to 1.500 inch 1.000 to 2.000 inch (or metric equivalent)
Comparative measurement of UUT reading to gage block test setup to test the basic length and micrometer head linearity.
UUT Length and Linearity
Equipment Requirements
Minimum Use Specifications
Calibration Equipment
Sub Item
Description Gage Block Set
Range: ± 0.05 to 4 inch Accuracy: ± 12 m in from stated value
L.S. Starrett Co. SS 36.A1
L.S. Starrett Co. SS 81.A1
Calibration Process.— 1) Set the UUT to indicate the minimum reading for the UUT using the ratchet or friction thimble. Assure that the reading indicates the minimum for the UUT model and range. If the reading is observed as off the minimum at this time, assure there is no foreign particle or burr on the anvil or spindle. An accurate zero indication must be estab- lished at this time as all other measurements will be affected by any error at zero. 2) The recommended size gage blocks used to test the micrometer spindle thread are very important. The recommended test points achieve the testing of the accuracy of the micrometer throughout the entire length and at points evenly distributed around the diam eter of the spindle thread. This verifies the accuracy of the lead error of the thread as well as identifying any sections that may have experienced excessive wear or damage. The recommended sizes are given in Table 16 :
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