Quick Guide to Precision Measuring Instruments
Roundtest (Roundform Measuring Instruments)
Geometrical tolerances ISO/DIS 1101: 1996* 1 , ISO 5459* 2
Roundness Any circumferential line must be contained within the tolerance zone formed between two coplanar circles with a difference in radii of t
Straightness Any line on the surface must lie within the tolerance zone formed between two parallel straight lines a distance t apart and in the direction specified
Flatness The surface must be contained within the tolerance zone formed between two parallel planes a distance t apart
Cylindricity The surface must be contained within the tolerance zone formed between two coaxial cylinders with a difference in radii of t
0.1
0.1
0.1
0.1
t
Notation example
Notation example
Notation example
t
Notation example
Tolerance zone
Tolerance zone
Tolerance zone
Tolerance zone
Verification example using a roundness measuring instrument Concentricity The center point must be contained within the tolerance zone formed by a circle of diameter t concentric with the datum
Verification example using a roundness measuring instrument Coaxiality The axis must be contained within the tolerance zone formed by a cylinder of diameter t concentric with the datum
Verification example using a roundness measuring instrument
Verification example using a roundness measuring instrument
Perpendicularity The line or surface must be contained within the tolerance zone formed between two planes a distance t apart and perpendicular to the datum
ø0.08 A
A
0.08 A
A
A
ø0.08
A
Notation example
Notation example
Notation example
A
ø0.08 A
øt
Notation example
Datum A
Datum center
Datum axis
Datum axis
Tolerance zone
Tolerance zone
Tolerance zone
Tolerance zone
Verification example using a roundness measuring instrument
Verification example using a roundness measuring instrument
Verification example using a roundness measuring instrument
Verification example using a roundness measuring instrument
Circular Runout (Radial and Axial) The line must be contained within the tolerance zone formed between two coplanar and/or concentric circles a distance t apart concentric with or perpendicular to the datum
Total Runout (Radial and Axial) The surface must be contained within the tolerance zone formed between two coaxial cylinders with a difference in radii of t, or planes a distance t apart, concentric with or perpendicular to the datum
Specified direction Radial - Direction that intersects the datum axial straight line and
Specified direction Axial - Direction that is parallel to the datum axial straight line
Specified direction Radial - Direction that intersects the datum axial straight line and
Specified direction Axial - Direction that is parallel to the datum axial straight line
0.1 A
0.1 A
0.1 A
0.1 A
A
A
A
A
is vertical to the datum axis line
is vertical to the datum axis line
Notation example
Notation example
Notation example
Notation example
t
J
Datum axis
Datum axis
Datum axis
Datum axis
Tolerance zone
Tolerance zone
Tolerance zone
Tolerance zone
Verification example using a roundness measuring instrument
Verification example using a roundness measuring instrument
Verification example using a roundness measuring instrument
Verification example using a roundness measuring instrument
Adjustment prior to Measurement ISO 4291: 1985* 3 Centering A displacement offset (eccentricity) between the Roundtest's turntable axis and that of the workpiece results in distortion of the measured form (limaçon error) and consequentially produces an error in the calculated 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. Some roundness testers support accurate measurement with a limaçon error correction function. The effectiveness of this function can be seen in the graph below.
Leveling Any 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 sufficiently parallel.
100
Effect of eccentricity compensation function
ø1 mm ø2 mm ø5 mm ø10 mm ø20 mm ø50 mm ø100 mm ø200 mm
1000
ø1 mm ø2 mm ø5 mm ø10 mm ø20 mm ø50 mm ø100 mm ø200 mm
10
θ
Workpiece Diameter
Workpiece Diameter
100
D
1
10
0.1
1
0.01
0.1
DL
0.001
0.01
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
e
D
1
10
100
1000
Inclination versus elliptic error Inclination (degrees)
Eccentricity (µm)
Eccentricity versus roundness error
J-27
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