1. Always stop the work before you take ameasurement. DO NOT measure moving parts becausethe micrometer may get caught in the rotating work andbe severely damaged.2. Always open a micrometer by holding the framewith one hand and turning the knurled sleeve with theother hand. Never open a micrometer by twirling theframe, because such practice will put unnecessary strainon the instrument and cause excessive wear of thethreads.3. Apply only moderate force to the knurledthimble when you take a measurement. Always use thefriction slip ratchet if there is one on the instrument. Toomuch pressure on the knurled sleeve will not only resultin an inaccurate reading, but also will cause the frameto spring and force the measuring surface out of line.4. When a micrometer is not in use, place it whereit will not drop. Dropping a micrometer will cause themicrometer frame to spring. If you drop a micrometer,check it for accuracy before you take further readings.5. Before you store a micrometer, back the spindleaway from the anvil, wipe all exterior surfaces with aclean, soft cloth, and coat the surfaces with a light oil.Do not reset the measuring surfaces to close contactbecause the protecting film of oil on these surfaces willbe squeezed out.SNAP GAUGEThe snap gauge compares the outside diameters ofparts such as shafts and journals to a standard. It cancompare diameters from zero to 8 inches at an accuracyof 0.0001 inch. Figure 2-5 shows a typical snap gauge.Most snap gauges consist of a frame with aninsulated handle, a hex wrench mounted in the handle,dial indicator digits calibrated in 0.00l-inch divisions, abezel clamp, adjustment wheels, locking wheels, abackstop, a lower anvil, an upper anvil, and a guard.Whenever you use a snap gauge, use the handle andavoid touching the gauge proper because body heat mayaffect the reading. For the same reason, handle thestandard plugs only by their plastic end. Clean the anvilsand the backstop with a clean cloth. To use the snapgauge, follow the manufacturer’s operating instructions.After you record the readings and compare thereadings with the design specifications, clean and storethe snap gauge in its appropriate storage location.Figure 2-5.—Typical snap gauge.BORE GAUGESThe dial bore gauge is one of the most accurate toolsfor measuring a cylindrical bore or for checking a borefor out-of-roundness or taper. The gauge does not givea direct measurement. It identifies the amount ofdeviation from a preset size or the amount of deviationfrom one part of the bore to another. A master ring gauge,outside micrometer, or vernier caliper can be used topreset the gauge. Figure 2-6 shows a typical bore gauge.Figure 2-6.—Typical bore gauge.2-4
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