Roundtest (Roundform Measuring Instruments)
Quick Guide to Precision Measuring Instruments
Roundtest (Roundform Measuring Instruments) ■ JIS B 7451-1997: Roundness measuring instruments ■ JIS B 0621-1984: Definition and notation of geometric deviations ■ JIS B 0021-1998: Geometric property specifications (GPS) of products– Geometric tolerance Roundness Testing Roundness Straightness Flatness Cylindricity Any circumferential line must be contained within Any line on the surface must lie within the The surface must be contained within the The surface must be contained within the the tolerance zone formed between two coplanar tolerance zone formed between two parallel straight tolerance zone formed between two parallel tolerance zone formed between two coaxial circles with a difference in radii of t lines a distance t apart and in the direction specified planes a distance t apart cylinders with a difference in radii of t
0.1 0.1 0.1 0.1 t
Notation example Notation example Notation example t t
Notation example
t
Tolerance zone Tolerance zone Tolerance zone Tolerance zone Inspection example Inspection example Inspection example Inspection example Concentricity Coaxiality Perpendicularity The center point must be contained within the The axis must be contained within the tolerance The line or surface must be contained within the tolerance zone formed between two planes a tolerance zone formed by a circle of diameter t zone formed by a cylinder of diameter t distance t apart and perpendicular to the datum concentric with the datum concentric with the datum A ø0.08 A A 0.08 A ø0.08 A A
Notation example Notation example A ø0.08 A Notation example øt øt Notation example øt
Datum A
Datum t center Datum axis Datum axis Tolerance zone Tolerance zone Inspection example Inspection example Inspection example Tolerance zone Inspection example Tolerance zone Circular Runout Total Runout The line must be contained within the tolerance zone formed between two coplanar and/or concentric The surface must be contained within the tolerance zone formed between two coaxial cylinders with a circles a distance t apart concentric with or perpendicular to the datum difference in radii of t, or planes a distance t apart, concentric with or perpendicular to the datum
Radial Runout 0.1 A Axial Runout 0.1 A Total Radial Runout 0.1 A Total Axial Runout 0.1 A A A A A
Notation example Notation Notation example Notation example example
t t
t t Datum axis Datum axis Datum axis Datum axis Inspection example Tolerance zone Inspection example Tolerance zone Inspection example Tolerance zone Inspection example Tolerance zone ■ Adjustment prior to Measurement Centering Leveling A displacement offset (eccentricity) between the Roundtest's rotary table axis and that of the workpiece Any inclination of the axis of a workpiece with respect to the rotational axis of the measuring results in distortion of the measured form (limaçon error) and consequentially produces an error in the instrument will cause an elliptic error. Leveling must be performed so that these axes are sufficiently calculated roundness value. The larger the eccentricity, the larger is the error in calculated roundness. parallel. Therefore the workpiece should be centered (axes made coincident) before measurement. Some roundness testers support accurate measurement with a limaçon error correction function. The effectiveness of this function can be seen in the graph below. 100 Effect of eccentricity compensation function ø1mm 1000 ø200mm ø2mm 10 θ ø100mm ø5mm ø50mm 100 ø10mm Workpiece Workpiece ø20mm ø20mm Dimeter D 1 Dimeter ø50mm ø10mm ø5mm 10 ø100mm ø200mm ø2mm 0.1 ø1mm 1 Error due to inclination (µm) Roundness error (µm) 0.01 0.1
Eccentricity 0.001 0.01 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1 10 100 1000 D e Eccentricity (µm) Inclination (degrees) Figure: Eccentricity versus roundness error Figure: Inclination versus elliptic error
Quick Guide to Precision Measuring Instruments 42 ■ JIS B 7451-1997: Roundness measuring instruments ■ JIS B 0621-1984: Definition and notation of geometric deviations ■ JIS B 0021-1998: Geometric property specifications (GPS) of products– Geometric tolerance Roundness Testing ■ Effect of Filter Settings on the Measured Profile ■ Undulations Per Revolution (UPR) data in Roundness values as measured are greatly affected by variation of filter cutoff value. It is necessary to set the filter appropriately for the evaluation required. the roundness graphs Measurement result graphs 90 No filter ΔZq=22.14µm
180 0 0 0 90 180 270 360 Amplitude
270 Angle
A 1 UPR condition indicates eccentricity of the workpiece relative to the rotational axis of the measuring instrument. The amplitude of undulation components Low-pass ΔZq=12.35µm ΔZq=16.60µm ΔZq=20.72µm ΔZq=22.04µm depends on the leveling adjustment. filter
90
180 0 0 0 90 180 270 360
15 upr 50 upr 150 upr 500 upr Amplitude
ΔZq=17.61µm ΔZq=18.76µm ΔZq=14.50µm Band-pass 270 Angle filter A 2 UPR condition may indicate: (1) insufficient leveling adjustment on the measuring instrument; (2) circular runout due to incorrect mounting of the workpiece on the machine tool that created its shape; (3) the form of the workpiece is elliptical by design as in, for example, an IC-engine piston.
90
15-150 upr 15-500 upr 50-500 upr
180 0 0 0 90 180 270 360
■ Evaluating the Measured Profile Roundness Amplitude Roundness testers use the measurement data to generate reference circles whose dimensions define the roundness 270 value. There are four methods of generating these circles, as shown below, and each method has individual Angle characteristics so the method that best matches the function of the workpiece should be chosen. A 3 to 5 UPR condition may indicate: (1) Deformation due to over-tightening of the Least Square Circle Minimum Zone Circles Minimum Circumscribed Maximum inscribed holding chuck on the measuring instrument; (2) Relaxation deformation due to (LSC) Method (MZC) Method Circle (MCC) Method Circle (MIC) Method stress release after unloading from the holding chuck on the machine tool that A circle is fitted to the measured Two concentric circles are The smallest circle that can enclose The largest circle that can be created its shape. profile such that the sum of the positioned to enclose the the measured profile is created. enclosed by the profile data is squares of the departure of the measured profile such that their The roundness figure is then created. The roundness figure is profile data from this circle is a radial difference is a minimum. defined as the maximum then defined as the maximum minimum. The roundness figure is The roundness figure is then departure of the profile from this departure of the profile from this 90 then defined as the difference defined as the radial separation of circle. This circle is sometimes circle. This circle is sometimes between the maximum departures these two circles. referred to as the ‘ring gage’ referred to as the `plug gage' of the profile from this circle circle. circle. (highest peak to the lowest 180 0 0 valley). 0 90 180 270 360 Amplitude
270 Angle ΔZq ΔZz ΔZc ΔZi 90
Rmin Rmin Rmin Rmin Rmax Rmax Rmax Rmax
180 0 0 0 90 180 270 360 Amplitude
ΔZq = Rmax-Rmin ΔZz = Rmax-Rmin ΔZc = Rmax-Rmin ΔZi = Rmax-Rmin 270 Angle
A 5 to 15 UPR condition often indicates unbalance factors in the machining method or processes used to produce the workpiece. 90 ■ Traceability System for Roundform Measuring Instruments (Traceability to PTB*) 180 0 0 0 90 180 270 360 PTB Calibration Straightness PTB Calibration PTB Calibration PTB Calibration NMI Amplitude Master (600mm) Optical Flat Reference Hemisphere Cylindrical Square PTB mutual Accreditation 270 Angle Mitutoyo Corporation 90 Miyazaki Plant NKO K107
180 0 0 Reference Calibration 0 90 180 270 360 Sphere Gauge Block Measuring Amplitude Instrument Calibration Tester 270 Angle
A 15 (or more) UPR condition is usually caused by tool chatter, machine vibration, coolant delivery effects, material non-homogeneity, etc., and is generally more
Roundness/Cylindrical Geometry Measuring Instrument Reference Hemisphere Magnification Calibration Kit 180 0 0 0 90 180 270 360
*PTB: Physikalisch-Technische Bundesanstalt (Germany) Amplitude
270 Angle ■ Stylus Tip 90 Ball type Cylinder type Axe type Egg type Tip shape: Ball, axe, cylinder, R and egg
r R 180 0 r r R r Tip radius : 0.25mm, 0.8mm, 0 r 2.5mm, 8mm, 25mm 0 90 180 270 360
r r (tolerance: 30% Amplitude of the nominal value) Measuring force: 250mN or less 270 Angle
43 Quick Guide to Precision Measuring Instruments