You read an inch system micrometer by looking at the division on the sleeve and thimble. The spindle screw is made so that one revolution moves the spindle 0.025 inch toward or away from the anvil . This means that 40 turns of the screw will move the spindle exactly 1 inch (40 ├Ś0.025=1.000).
A scale on the sleeve is divided into 40 divisions. Each division is equal to 0.025 inch. Start with the spindle against the anvil and turn the screw out. Every revolution of the thimble uncovers one of the division on the sleeve. Every fourth division on the sleeves is numbered. The numbers start with the zero mark when the spindle is against the anvil. The next numbered division is at 0.100 inch (1/10 of an inch) from the closed position . The three unnumbered divisions between zero and one are at 0.025, 0.050. And 0.075 inch.
The bevel on the front of the thimble is also division into equal parts. Since the thimble and spindle travel 0.025 inch per revolution , there are 25 divisions on the bevel. These divisions allow you to read the amount of spindle travel for a part of a revolution. A revolution from one thimble mark to the next is 1/25 of a revolution . This moves the spindle 0.001 inch.
You read a micrometer measurement by addition . Add together:
1. The last visible numbered division on the sleeve
2. The unnumbered sleeve divisions
3. The divisions on the bevel of the thimble
4. The total is your measurement
An easy way to remember is to think of the units as making change from a ´╣?0 bill. Count the figures on the sleeve as dollars the vertical lines on the sleeve as quarters , and the divisions on the thimble as cents. Add up the change and put a decimal point instead of a dollar sign in front of the numbers.
The most common size micrometer is 0-1 inch. This size can be used to measure a part that is less than 1 inch. Micrometer are made in other sizes such as 1 to 2 inches, 2 to 3 inches, and larger to measure large components . large micrometers are read in the same way as the 0-1 inch micrometer.
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