Roundness measurement Evaluations

Roundness measurement

Roundness is defined as the condition of a surface of revolution. In the case of cylinders and cones,all points of the surface intersect any plane perpendicular to a common axis.

Equipment for measuring roundness

1) Diameter gauge.

2) Circumferential conferring gauge => the shaft is constrained in the ring gauge and rotates relative to the set indicator probe.

3) Center rotation.

4) V-block.

5) Three-point probe. 

6) Accurate spindle.

1.Radial method.

The measuring plunger is positioned at 180° of the part and measures the diameter at multiple positions.This method is only applicable if the specimen is oval or has an even number of lobes.A diameter check will not necessarily reveal a valid size or roundness.This method is not reliable for determining roundness.

2.Circumferential gauge

The principle of Useful for roundness checks in production.This method requires highly accurate masters to measure each size of the part.Clearance between parts and gauges is critical to reliability.This technique does not allow the measurement of other relevant geometric features such as concentricity,shoulder flatness, etc.

3.Center rotation

When mounted on center,check shaft for roundness.In this case,reliability depends on many factors such as center angle,center alignment,center and center hole roundness and surface condition,and part runout.Unevenness of the part can cause a double runout effect that manifests as a roundness error.

4.V-block

The setup used to evaluate the roundness error by using the V Block.The V block is placed on the platform,and the workpiece to be inspected is placed on it. The diameter indicator is fixed on the support,and its antennae rest on the surface of the workpiece.Rotate the workpiece to measure the rise and fall of the workpiece.To determine the number of lobes on a workpiece,the workpiece is first tested in a 60° V-block and then in a 90° V-block.The number of lobes then equals the number of times the indicator pointer deflects through a 360° rotation of the workpiece

Limitations

a) The roundness error is greatly affected by the following factors.

(i) If the roundness error is i\e,there may be no change in the indicator.

(ii) The position of the instrument,that is,whether it is measured from the top or the bottom.

(iii) Number of lobes on rotating parts.

b) The position of the instrument should be in the same vertical plane as the point of contact of the part with the V-block.

c) The leaf spring should remain below the indicator plunger and part surface at all times.

5.Three-point probe

Roundness Measuring Axis

The following two types of spindles are used.

1.Elevated spindle

The part is fixed on a platform,and the overhead spindle carrying the comparator rotates separately from the part.It can determine roundness and cam (circular flatness).The height of the workpiece is limited by the position of the overhead spindle.Concentricity can be checked by extending the indicator from the spindle,so the inspection range is limited.

2.Rotary table

The main shaft is integrated with the worktable and rotates together with the worktable.The part is placed on the spindle and rotated past the fixed comparator.