ANGULAR MEASUREMENT-SINE BAR

A sine bar is a tool used to measure angles in Metalworking

ANGULAR MEASUREMENT-SINE BAR

Uses sine principal -- Measurement usually limited to 45 degree due to loss of accuracy pt of view.

Sine bar used in conjunction with slip gauges

Important parameters

Made from high carbon, high chromium, corrosion resistant steel, hardened, ground stabilized.

Two cylinders of equal diameter are attached at the ends.

Axis of cylinder parallel to each other and parallel to and at equal distance from upper surface of sine bar.

SINE BAR – working principal

Angles are measured using a sine bar with the help of gauge blocks and a dial gauge or a spirit level. The aim of a measurement is to make the surface on which the dial gauge or spirit level is placed horizontal. For example, to measure the angle of a wedge, the wedge is placed on a horizontal table. The sine bar is placed over the inclined surface of the wedge. At this position, the top surface of the sine bar is inclined the same amount as the wedge. Using gauge blocks, the top surface is made horizontal. The sine of the angle of inclination of the wedge is the ratio of the height of the gauge blocks used and the distance between the centers of the cylinders.

USE OF SINE BAR

lh

Sin θ = h l

1.CHECKING OF UNKNOWN ANGLE ‘θ ’ OF WORKPIECE

θ

USE OF SINE BAR

2.MEASURING KNOWN ANGLES OR LOCATING ANY WORK TO A GIVEN ANGLE

Knowing θ , ‘h’ can be found out and any work could be set at that angle asThe top face of sine bar is inclined at Angle θ to the surface plate.

USE OF SINE BAR –

3.CKECKING OF UNKNOWN ANGLES OF HEAVY COMPONENT

Sine bar mounted on component .The height over the rollers can then be measured with vernier height gauge. Differene of two readings of height gauge divided by centre distance of sine bar gives sine of angle of component to measure.

component

Sine bar

h2h1

Sine bar impractical to use above 45 degree

Physically clumsy to hold.

Slight error of sine bar causes large angular error.

Temperature variation becomes critical.

Body of sine bar obstructs gauge block stack.

PRECAUTION

Should not be used for angle greater than 60 degree.

Compound angle should not be formed by misalignment of work piece.

Accuracy of sine bar to be ensured.

Longer sine bar used as many error reduced by using longer bar.

SINE BAR – types

Sine centreA special type of sine bar is sine centre which is used for conical objects having male and female parts. It cannot measure the angle more than 45 degrees.

Sine tableSine table (or sine plate) is used to measure angles of large workpieces.

Compound sine tableIt is used to measure compound angles of large workpieces. In this case, two sine tables are mounted one over the other at right angles. The tables can be twisted to get the required alignment.

AUTOCOLLIMATOR

OPTICAL INSRUMENT FOR MEASUREMENT OF SMALL ANGULAR DIFFERENCE

Principles of operation

The autocollimator projects a beam of collimated light. An external reflector reflects all or part of the beam back into the instrument where the beam is focused and detected by a photodetector. The autocollimator measures the deviation between the emitted beam and the reflected beam. Because the autocollimator uses light to measure angles, it never comes into contact with the test surface.

Principles of operation

Principles of operation

Principles of operation

Like in the collimator the image of the illuminated object reticle is projected by the objective lens to infinity. In some distance, the collimated beam is reflected back from a mirrored surface .If the mirror surface is tilted by an angle α with respect to the optical axis, the reflected beam will enter the objective lens with an angle 2α. This leads to a shift d of the image in the image plane which can be calculated with the objective focal length f giving d = 2α x f or α = d/( 2f ). Thus, the sample angle is directly proportional to the measured shift in the image plane (small angles assumed). The resolution of an autocollimator increases proportionally and the angular field of view reciprocally with the focal length of the objective lens.

ANGLE GAUGES

1)Direct use of angle gauges to measure the angle in die insert2)Use of angle gauges with square plate.