Everything about Standard Design Micrometers

Standard Design Micrometers

For all of our standard micrometers

Measuring Face

	Interference fringes number of spindle measuring face: s M=2	The flatness and parallelism of measuring faces are tested by optical flat. Because of roughness of measuring faces, after optical flat contact with measuring face of spindle or anvil, there are gaps between faces, thereby interference fringes and rings appear.At vertical direction to measuring faces, each interference fringe or ring represents 0.3um of flatness error.
	Interference fringes number of anvil measuring faces: N=2 Interference fringes number of two measuring faces: K=M+N=2+2=4 Parallelism of two measuring faces: 4x0.3=1.2μm	Parallelism error of measuring: face To test parallelism of two measuring faces of micrometers with upper range under 100mm, by optical flat specified with 1/3 or 1/4 of screw pitch of micrometer spindle. In turns, put optical flat between two measuring faces, turn measuring force by 5-10, to make optical flat and measuring faces touched. Then rotate optical flat slowly to make interference fringes or rings reduced to the least.  For micrometers with range over 100mm, autocollimator can be used to test parallelism of measuring faces. Parallelism error near edge zone within 0.4mm of measuring face shall be disregarded.
	Interference fringes number of anvil measuring faces: N=1 Parallelism of anvil measuring faces: 1x0.3=0.3μm	Flatness error of measuring ：face To testing flatness and parallelism of measuring faces by second-class optical flat, adjust the flat to make interference band or ring to the least, ot to make to be closed interferencering. Interference bands or rings with same color should not appeared over two stripes. (Flatness of measuring faces: <0.6μm). Flatness error near edge zone within 0.4mm of measuring face shall be disregarded.
Micrometers
		Measuring force device: Measuring force device is used to drive spindle and ensure measuring force of the measure face invariable, acquire precise measuring results. Ratchet stop: Normal micrometers have ractet stop. Notices when measuring workpiece by ratchet stop

Measuring Technology Information- Various Errors

Visual error

For reticles on sleeve and thimble are not in a same planeˈthere appears visual error when reading on thimble from different points Aˈ B and C. Therefore, line of sight perpendicular to reticles on the sleeve (Point B as shown in picture). If read from point A or C, there is reading error about 2 μm. So, line of sight must be attended when reading.

Position error

Distortion of frame should be taken into account when using large micrometers. During measuring, ensure direction of measuring coincident with that of setting.

Temperature error

Infection of temperature should be taken into account when using large micrometers. For 1 meter long workpiece made of steel (as gauge block), there is error about 11 μm as temperature changing one degree. Because of different material of gauge block and micrometers, when temperature change similarly, change of their length are different. Therefore, when calibrating, keep micrometers and workpiece in place with stable temperature for enough time (3 hours) and keep temperature within [(20±2°C)].

Airy points

Airy points, supposition of optimal curving points to support boday of setting standard or tubular inside micrometer in level.

Airy points, supposition supporting two points, enable two sides surfaces parallel.

b=0.5577L

Abbe principium

Abbe principium Abbe principium says: “Only when datum lines of measuring system and measured workpiece are on a same line, measurement is most accuracy.” As drawing shows, when there is distance (h) between measuring faces and reading axis line, there will be measuring error ( ). Therefore, measuring force must be taken into accounted during such measurement.

ε = b-a = h tan θ