Roundness and Circularity

Presented by,

KIRAN M.

2

Contents

Introduction

Types of irregularities

Roundness and circularity

Methods of roundness measurement

Modern Machines

References

3

Introduction

For assembly not only dimensional tolerance ,but also the geometrical accuracy is need.

Clamping distortion, spindle run-out, presence of dirt and chips in clamping surface are main causes of out of roundness.

4

Types of Irregularities

a. Ovality

b. Lobing

c. No specific form

5

Roundness and Circularity

Roundness is defined as the condition of a surface of revolution, where all point of the surface is intersected by any plane perpendicular to common axis are equidistant from the axis.

Axis and center do not exist physically, so measurement has to be made with reference to surface.

It is circular contour.

Measuring roundness is only the circularity of the contour.

6

Methods of Roundness Measurement

1. Micrometer/ Vernier Method (Diametrical)

2. V block and dial indicator (Chordal)

3. Bench center method (Radial)

4. Roundness measuring machine

7

1. Micrometer/Vernier Method (Diametrical)

Simple ordinary micrometer or vernier caliper is used.

Measurement will be within limits but shape may not be circular, only can be identified when assembled.

8

2. V block and Dial indicator (Chordal)

V - block is placed on a surface plate and the work to be checked is placed upon it.

Sensitive dial indicator is firmly fixed in a stand and its feeler made to rest against the surface of the work.

Work is rotated to measure the rise and fall of the work-piece.

Tested in two v blocks 60° and 90°.

9

Cont..

No. of lobes = no. of times indicator deflects during 360° rotation of work piece.

Measurement affected by: Angle of block. Position of instrument. No. of lobes in work piece.

10

Polar Graph

Actual shape of the work-piece can be had by actually plotting the polar graph.

First of all 12 markings equally space at angles of 30° are made on the face of the work-piece to be measured.

The work-piece after properly cleaning is then placed on the V-block

Dial indicator is placed just above the work-piece so that it is touching the work-piece nearly at the centre of the V-block.

Work-piece is then rotated such that the marking on the work-piece is below the indicator plunger.

Readings of the dial indicator are noted down for all the markings.

11

Cont..

Suitable scale is chosen depending on the maximum value of the reading.

Circle of diameter nearly 4 times the maximum reading of the dial indicator is drawn and is divided into 12 number of angular divisions .

Inside the outer circle, another concentric circle of suitable diameter is drawn.

Values of the indicator are plotted in radial direction taking the smaller circle as the reference circle in order that both the positive and negative readings are plotted within the prepared graph.

12

3. Bench Center Method (Radial)

Some parts, (such as shafts) may be inspected for roundness while mounted on centres.

Reliability dependents on factors like angles of centres, alignment of centres, roundness and surface condition of the centres and centre holes, and runout of piece.

13

4. Roundness Measuring Machine

Two kinds : Overhead spindle - part is fixed on a platform and

the overhead spindle carrying the comparator rotates separately. Height of the work-piece is limited by the location of overhead spindle. Since the workpiece is stationary and separate from the spindle, the spindle is not affected by load of workpiece.

Rotating table - spindle is integral with the table and rotates with it. Part is placed over the spindle and rotates past a fixed comparator. Weight of workpiece may result in inaccuracy since it has to be supported on the rotating spindle

14

Modern Machines

Roundtest RA-H5100 by Mitutoyo is most modern instrument in this field.

ROCKPAK measuring and

analysis software.

15

References

Engineering Metrology – R. K. Jain Engineering Metrology – I. C. Gupta www.what-when-how.com/metrology/measurement-of-circularity/

16