It is a study of measurement.

1. Feature Inspection of Circularity and
Roundness
By – A.PRASANTH
(2017PPE8004)

2. INTRODUCTION –
Metrology is a branch of science which deals with the study of
measurement.
Metrology is divided into three basic overlapping activities.
definition of measurement units,
realization of these units of measurement in practice,
Traceability i.e. linking measurements made in practice to the reference
standards
Circular parts not only depends upon diametrical tolerance but also
on the geometrical accuracy.

3. Two Content Layout with Table
 detects the various possible errors of circularity.
Cont..

4. INSPECTION OF CIRCULARITY AND ROUNDNESS
ROUNDNESS – It is the condition of a surface of revolution, where all points on the
surface are equidistant from the central axis. The characteristic of roundness greatly
depends upon the method of generation.
roundness analysis can be performed with the addition of harmonic and slope analysis.
CIRCULARITY – when all points of a surface of revolution at any cross-section are the
same distance away from a common axis or center point.
The error of circularity is defined as the radial distance between the
minimum circumscribing circle and the maximum inscribing circle, which contain the
profile of the surface at a section perpendicular to the axis of rotation.
Cylindricity analysis can be done by collecting data from upto ten planes along a
cylindrical component

5. MEASUREMENT OF ROUNDNESS
 The most commonly used devices for measurement of roundness are –
 Diametral Method –
 In this method, the measuring plungers are located 180°
apart and the diameter is measured at several places.
 This method is suitable only when the specimen is elliptical or has an even
number of lobes.
 Diametral check does not necessarily disclose effective size or roundness.
 This method is unreliable in determining roundness.
 Circumferential confining gauge method –
 This method requires a separate highly accurate master for each size part to
be measured.
 This technique does not allow the measurement of other related geometric
characteristics, such as concentricity, flatness of shoulders, etc.

6. Cont..
• The clearance between part and gauge is critical to reliability.
• The values obtained dependents upon the shape of the specimen.
• Rotating on centres method –
• In this method, reliability dependents on many factors like angles of
centres, alignment of centres, roundness and surface condition of the
centres, centre holes and runout of piece.
• Out-of-straightness of the part will cause a doubling runout effect and
appear to be roundness error.

7. Cont.
• V – Block method –
• It is further divided into two method –
• workpiece rotating against a set probe of fixed angle
• workpiece rotating against a set probe of adjustable angle
• Due to the difficulties faced during the determination of number of lobes.
• V-Block method is limited in the determination of roundness of parts because it is
suitable only when the number of lobes is known and is uniformly arranged, which is
never the case.
Lobes Angle of V-block
Three-point out of roundness 60°
Five-Iobed part 108°
Seven-lobed part 128° 34′

8. Cont..
• Three-Point Probe method –
• Accurate spindle method –
• It is a method to provide a definitive value for calibration of roundness.
• There are several types of spindle designs available for generation and
inspection of round shapes.
• Various designs are –
• ball bearings,
• roller bearings,
• plain ball spindles,
• plain bearings (journal type),
• metered oil flow and fluid-bearing
(gas bearing and oil-bearing).
• The three-probe with 120° spacing is very useful
for determining effective size in cases of doubtful
geometry.
• Show partial error for randomly spaced lobes.

9. DIFFERENT TYPES OF IRREGULARITIES OF CIRCULAR PART
The error of circularity of cross section can be classified by –
• Oval
• Lobbing
• No specific form

10. Add a Slide Title - 2Out of Roundness
 It is the greatest distance from the actual cross sectional surface to the
surrounding circle of points.
 Out-of-roundness gauges are used to check internal and external cylindrical
surfaces.
 It is affected by –
 clamping distortion,
 spindle run-out,
 Presence of dirt,
 chips on clamping surfaces,
 imbalance,
 heat and vibration.

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Reference Circle
The value for the out-of-roundness of any particular profile can be obtained by the
following reference circles –
• Least squares circle –
• This circle represents the average of all the
peaks and valleys of the profile.
• It is the sum of squares of a sufficient number of
equally spaced radial ordinates, measured from
the circle to the profile has minimum value.
• The centre of such a circle is known as the Least
Squares Centre (L.S.C.).
• The value of out of roundness is the radial
distance of the maximum peak from this circle
(P) plus the distance of the maximum valley
from this circle (V) i.e. P + V.

12. Cont..
Minimum zone or minimum radial separation circles –
• These are two concentric circles that just enclose the
profile and which have minimum radial separation.
• The centre of such a circle is termed as the minimum
zone centre.
• The value of out-of-roundness is the radial distance
between the two circles.
Maximum inscribed circle –
• It is the largest circle that can be drawn inside the
profile without cutting it.
• The value of out of roundness is specified as the height
of the largest peak above the circle.

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Cont..
Minimum circumscribed circle –
• It is the smallest circle that will completely enclose
the profile without cutting it.
• The value of out-of-roundness is the distance of
the lowest valley from the circle.

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MODERN ROUNDNESS MEASURING INSTRUMENTS
• The modern roundness measuring instruments are microprocessor based
instrument, which provide quickly and easy way of measurements.
• Machine can do centering and calculation of roundness, concentricity,
straightness and provide visual and digital displays.
• There are two basic types of roundness measuring systems –
• Rotating worktable – In this device, workpiece is rotated and pick up
is stationary.
• Rotating spindle – In this device, workpiece is stationary and pick up
is rotated.

15. Roundness Measuring Spindles