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The Outside Micrometer Everything you need to know about the Imperial micrometer 1 2 2”-3” 1”-2” 0-1” Calibration standards Spanner wrenches 3 The Fundamentals Parts of a micrometer How to hold a micrometer How to position the measuring faces How tight when measuring How to read an imperial micrometer Accuracy to 0.001 of an inch Imperial micrometer Sleeve Has 40 graduations along its length of 1 inch Each graduation is 1/40 of an inch =0.025inches Every 4th graduation is larger =1/10 of an inch or =0.1 inch The Thimble This is the part that is turned The thimble scale has 25 graduations around the thimble that is numbered 025 Each graduation =0.001 inch This gives accuracy to 0.001 inch The Ratchet Located at the end of the thimble Used to control the force or load applied to the micrometer while measuring Prevents the micrometer from being over tightened When max load is reached it will make a clicking sound. Some types use a sliding clutch The spindle The spindle is a plunger that moves in a linear direction One revolution of the thimble moves the spindle 0.025” or 1 graduation on the sleeve The spindle carries one of the measuring surfaces that contacts the object being measured The Frame and Anvil The frame is the main support member for all other parts of the micrometer The anvil is located in the far end of the frame and provides the fixed measuring surface The frame will have the size and type of micrometer marked on it They are usually made from cast iron The lock May be of a lever or a roll type Locks the spindle to the sleeve so that readings can be taken easily Allows you to capture the reading of the scales How to hold a micrometer Positioning How to Read a micrometer to .001” Sleeve: The micrometer sleeve is divided into forty equal parts. Each part or division is indicated by a vertical line. Each line represents one-fortieth of an inch or .025” and each fourth line is marked with a longer line which designates one hundred-thousandths. Simplified, the line marked “1” represents .100”, the line marked “2” represents .200” and so forth. Thimble: The thimble is divided into twenty-five equal parts and one complete rotation of the thimble coincides with the smallest division on the sleeve. Thus the division on the thimble is one-twenty-fifth of .025” or .001”. Reading Example: (see illustration to right) 1. Note that the thimble has stopped at a point beyond “2” on the sleeve indicating .200”. 2. Note that one additional line is visible between the graduation numbered “2” and the edge of the thimble , indicating .025”. 3. The line numbered “1” on the thimble coincides with the line on the sleeve. It means an additional one-thousandth of an inch. _________________________________________________ 1) Reading on the sleeve…………………….. .200” 2) No. lines between “2” and the edge of thimble……………………….. .025” 3) Thimble line corresponding to center line of sleeve…………………… .001” TOTAL READING…………………….. .226” How to Read a micrometer to .0001” To read to one ten-thousandth of an inch requires an additional scale called the “Vernier” scale, named after the inventor, Pierre Vernier. In the case of a regular micrometer, the Vernier consists of ten divisions, marked on the sleeve. Which are spaced within nine divisions of the thimble scale. Therefore each division on the Vernier is one-tenth shorter than that of the thimble’s, thus representing .0001”. Reading Example: (see illustration to right) 1. Note that the thimble has stopped at a point beyond “2” on the sleeve indicating .200”. 2. Note that one additional line is visible between the graduation numbered “2” and the edge of the thimble , indicating .025”. 3. The line numbered “1” on the thimble coincides with the line on the sleeve. It means an additional one-thousandth of an inch. 4. Note that the Vernier line numbered “2” coincides exactly with the thimble line indicating .0002”. _________________________________________________ 1) Reading on the sleeve…………………….. .200” 2) No. lines between “2” and the edge of thimble……………………….. .025” 3) Thimble line corresponding to center line of sleeve…………………… .001” 4) Vernier line coincides exactly with thimble line………………………… .0002” TOTAL READING…………………….. .2262” Let’s practice what we have learned Let’s practice what we have learned .225 .200 .487 .250 .304