C-50CMitutoyo reserves the right to change any or all aspects of any product specication, including prices, designs and service content, without notice.C-50C04535405109876ThimbleOuter sleeve■ How to Read the Scale(1) Outer sleeve 35 mm(2) Thimble 0.015 mm Reading 35.015 mmGraduation 0.005 mm(2)(1)Changes in measured values at different measuring pointsHow to Read the ScaleThe accuracy of a Holtest is maximized if the same part of the anvils is used for measurement as was used for standardizing the instrument with a setting ring.When you use the tip of the anvil for measurement, adjust the datum point using the tip of the anvil.45051DIV. 0.005mm454WorkpieceAdjustment ofstart point45051DIV. 0.005mm4549401DIV. 0.005mm50459401DIV. 0.005mm5045Adjustment ofdatum pointWorkpieceaaaaAiry and Bessel PointsWhen a length standard bar or inside micrometer lies horizontally, supported as simply as possible at two points, it bends under its own weight into a shape that depends on the spacing of those points. There are two distances between the points that control this deformation in useful ways, as shown below. The ends of a bar (or micrometer) can be made exactly horizontal by spacing the two supports symmetrically as shown above. These points are known as the ‘Airy Points’ and are commonly used to ensure that the ends of a length bar are parallel to one another, so that the length is well dened.The change in length of a bar (or micrometer) due to bending can be minimized by spacing the two supports symmetrically as shown above. These points are known as the ‘Bessel Points’ and may be useful when using a long inside micrometer.If the Inside Micrometer is misaligned in the axial or radial direction by an offset distance X when a measurement is taken, as in Figures 1 and 2, then that measurement will be in error as shown in the graph below (constructed from the formulae given above). The error is positive for axial misalignment and negative for radial misalignment.Figure 1Effect of misalignment on accuracy (Inside Micrometer)Figure 2:Inside diameter to be measuredL:Length measured with axial offset XX:Offset in axial direction△:Error in measurement△:L−=√2+X2 −:Inside diameter to be measuredL:Length measured with radial offset XX:Offset in radial direction△:Error in measurement△:L−=√2–X2 −XXLL109876543210.100.090.080.070.060.050.040.030.020.01ℓ=200 mmℓ=500 mmℓ=1000 mmError (positive for axial, and negative for radial, misalignment) (mm)Misalignment (offset) of one end of micrometer (mm)Airy points (a 0.577)Bessel points (a 0.559)Reference point setting (2-point gages)• Reference point setting with a ring gage or cylinder master gage Insert the bore gage into the ring gage, vertically or horizontally swing the bore gage, and set the zero point to the point where the indicator reads the maximum value. (Rotate the dial face for a dial gage and perform presetting or zero setting for a Digimatic indicator.) • Reference point setting with outside micrometer and gauge blockHold a gauge block (of the reference dimension) between a micrometer’s measuring faces as if measuring the block. Clamp the micrometer's spindle and then pull out the gauge block. Insert the bore gage between the micrometer’s measuring faces. Maneuver the bore gage to the position where the indicator reads a minimum and then set the pointer to read zero (or a preset value required) by rotating the bezel. • Reference point setting with outside micrometer onlyFix the micrometer in a vertical attitude with its head side (spindle side) downward (see illustration below), and then adjust the distance between the measuring faces to the reference dimension. At this time, do not clamp the micrometer spindle. Insert the bore gage between the micrometer’s measuring faces. Maneuver the bore gage to the position where the indicator reads a minimum and then set the pointer to read zero (or a preset value required) by rotating the bezel. Zero-setting with a micrometer requires a certain degree of dexterity because no self-centering action is available, as is the case when using a setting gage. Zero-setting is also possible by performing the same procedure using the gauge block, Height Master, or bore gage zero checker in addition to the outside micrometer.0Measurement error due to temperature effects on an inside micrometerThe accuracy of an inside micrometer is degraded if its temperature is signicantly different from 20 °C. To help prevent this situation occurring wear gloves and only hold the micrometer by the heat insulators to reduce the transfer of heat from the operator's hands.