Quick Guide to Precision Measuring Instruments

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PG62RmaxRminΔZqRmaxRminΔZzRmaxRminΔZcRmaxRminΔZcDLDθDe0.010.101.0010.00100.001000.00ø1mmø2mmø5mmø10mmø20mmø50mmø100mmø200mm1101001000Eccentricity (µm)Eccentricity versus roundness errorInclination versus elliptic error ø1mmø2mmø5mmø10mmø20mmø50mmø100mmø200mm0.0010.0100.1001.00010.000100.00000.10.20.30.40.50.60.70.80.91Inclination (degrees)Error due to inclination (µm)Roundness error (µm) Evaluating the Measured Prole RoundnessRoundness testers use the measurement data to generate reference circles whose dimensions dene the roundness value. There are four methods of generating these circles, as shown below, and each method has individual characteristics so the method that best matches the function of the work-piece should be chosen. Each method results in a different center position for the reference circles and therefore affects the axial location of the circu-lar feature measured.Least Square Circle (LSC)Minimum Zone Circles (MZC) Minimum Circumscribed Circle (MCC)Maximum inscribed Circle (MIC)A circle is tted to the measured prole such that the sum of the squares of the departure of the prole data from this circle is a mini-mum. The roundness gure is then dened as the difference between the maximum deviation of the prole from this circle (high-est peak to the lowest valley).Two concentric circles are positioned to enclose the measured prole such that their radial difference is a minimum. The round-ness gure is then dened as the radial separation of these two circles.The smallest circle that can enclose the mea-sured prole is created. The roundness gure is then dened as the maximum deviation of the prole from this circle. This circle is some-times referred to as the ‘ring gage’ circle.The largest circle that can be enclosed by the prole data is created. The roundness gure is then dened as the maximum deviation of the prole from this circle. This circle is some-times referred to as the `plug gage' circle.ΔZq = Rmax-RminΔZq : A symbol indicating roundness value by LSC.ΔZz = Rmax-RminΔºZz : A symbol indicating roundness value by MZCΔZc = Rmax-RminΔºZc : A symbol indicating roundness value by MCC.ΔZi = Rmax-RminΔZi : A symbol indicating roundness value by MIC.Effect of eccentricity compensation functionInclination versus elliptic errorAdjustment prior to MeasurementCenteringA displacement offset (eccentricity) between the Roundtest's rotary table axis and that of the workpiece results in distortion of the mea-sured form (limaçon error) and consequentially produces an error in thecalculated roundness value. The larger the eccentricity, the larger is the error in calculated roundness.Therefore the workpiece should be centered (axes made coincident) before measurement. ort accurate measurement with a limaçon error correction function. The effectiveness of this function can be seen in the graph below.LevelingAny inclination of the axis of a workpiece with respect to the rotational axis of the measuring instrument will cause an elliptic error. Leveling must be performed so that these axes are sufciently parallel.Roundtest (Roundform Measuring Instruments)

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