Sine bar

SINE BAR

Sine bars are always used along with slip gauges as a device for the measurement of angles very precisely. They are used to

1) Measure angles very accurately.

2) Locate the work piece to a given angle with very high precision.

Generally, sine bars are made from high carbon, high chromium, and corrosion resistant steel. These materials are highly hardened, ground and stabilized. In sine bars, two cylinders of equal diameter are attached at lie ends with its axes are mutually parallel to each other. They are also at equal distance from the upper surface of the sine bar mostly the distance between the axes of two cylinders is 100mm, 200mm or 300mm. The working surfaces of the rollers are finished to 0.2µm R value. The cylindrical holes are provided to reduce the weight of the sine bar.

Working principle of sine bar

The working of sine bar is based on trigonometry principle. To measure the angle of a given specimen, one roller of the sine bar is placed on the surface plate and another one roller is placed over the surface of slip gauges. Now, ‘h be the he slip gauges and ‘L’ becenters,thenthe angledistancecalculatedas between

Use of Sine Bar

Locating   any’   work   to   a   given   angle

1)      Before checking the unknown angle of the specimen, first the angle (0) of given specimen is found approximately by bevel protractor.

2)      Then  the  sine  bar  is  set  at  angle  of  0  and  clamped on the angle plate.

3)      Now, the work is placed on the sine bar and the dial indicator set at one end of the work is moved across the work piece and deviation is noted.

4)      Slip gauges are adjusted so that the dial indicator reads zero throughout the work surface.

Limitations of sine bars

1) Sine bars are fairly reliable for angles than 15°.

2) It is physically difficult to hold in position.

3) Slight errors in sine bar cause larger angular errors.

4)                A difference of deformation occurs at the point of roller contact with the surface plate and to the gauge blocks.

5) The size of parts to be inspected by sine bar is limited.

Sources of error in sine bars

The different sources of errors are listed below:

1) Error in distance between roller centers.

2) Error in slip gauge combination.

3) Error in checking of parallelism.

4) Error in parallelism of roller axes with each other.

5) Error in flatness of the upper surface of sine bar.