Outside Micrometer Calipers Machinery's Handbook, 31st Edition
768
Vernier Clamp Ring or Lock Nut
Ratchet or Friction Stop
Anvil
0
20
Spindle
Thimble
Barrel
Vernier
Frame
0
3
4
2
0
1
20
Graduations
Reference Line
Fig. 1. Design Features of Type I, Class 1 Micrometer Frame: Frames of all outside micrometers in sizes from 1 ⁄ 2 inch to 4 inch shall be of steel. Frames of micrometers from 5 inch and greater shall be of steel, tubular steel or malleable iron. The Type I, Class 1 enameled frame shall have a cutaway back (Fig. 2a), long tapered back (Fig. 2b), or C-type Back (Fig. 2c), of either I-beam or hollow tubular steel frame con struction, and shall have either a smooth or rippled enameled finish.
Fig. 2a. Cut-Away Back Fig. 2c. C-Type Back Flexure: The cross section design and material used in the frame shall be, in combina tion, of sufficient design, that when a force of 2 pounds (10 N) is applied in parallel to the spindle axis upon the anvil, that a flexure of the frame shall not exceed the tolerance as specified in Table 8a and Table 8b. Fig. 2b. Long Taper Back Micrometer Screw Spindle: The entire micrometer screw spindle shall be hardened and stabilized to no less than 62 RC from a high grade or alloy steel. The thread form and all surfaces shall be precision ground and smoothly lapped. The thread form shall conform to ANSI/ASME B1.3-2007 (R2017), “Screw Thread Gaging Systems for Acceptability: Inch and Metric Screw Threads”, and be a UN 40 pitch for English measurements and a M 0.5 mm pitch for SI (metric) measurements. The cylindrical portion of micrometer screw spindle shall be a free turning fit to the frame bearing without bind or shake and move smoothly and freely through the entire length of travel. There shall be no backlash between the threaded portion and the nut and at the maximum reading, there shall be no less than 0.240 inch engagement of the nut on the threaded portion of the screw spindle. The thread lead shall be sufficiently accurate throughout the entire length so as to permit compliance to the tolerances defined in Table 8a and Table 8b. The diameter of the spindle shall be no less than 0.1875 ( 3 ⁄ 16 ) inch for 1 ⁄ 2 inch micrometers, and no less than 0.2343 ( 15 ⁄ 64 ) inch
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