- Sine bar
A

**sine bar**is a tool used to measure angles inmetalworking .It consists of a hardened, precision ground body with two precision ground cylinders fixed at the ends. The distance between the centers of the cylinders is precisely controlled, and the top of the bar is parallel to a line through the centers of the two rollers. The dimension between the two rollers is chosen to be a whole number (for ease of later calculations) and forms the of a triangle when in use. The image shows a 10 inch and a 100 mm sine bar.

When a sine bar is placed on a level surface the top edge will be parallel to that surface. If one roller is raised by a known distance, usually using

gauge blocks , then the top edge of the bar will be tilted by the same amount forming an angle that may be calculated by the application of the sine rule.*The hypotenuse is a constant dimension — (100 mm or 10 inches in the examples shown).

*The height is obtained from the dimension between the bottom of one roller and the table's surface.

*The angle is calculated by using the sine rule. $sin\; left(angle\; ight)\; =\; \{opposite\; over\; hypotenuse\}$Angles may be measured or set with this tool.

**Principle**Angles are measured using a sine bar with the help of

gauge blocks and adial gauge or aspirit 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 awedge , thewedge is placed on a horizontal table. Thesine bar is placed over the inclined surface of thewedge . At this position, the top surface of thesine bar is inclined the same amount as the wedge. Usinggauge blocks , the top surface is made horizontal. The sine of the angle of inclination of thewedge is the ratio of the height of thegauge blocks used and the distance between the centers of the cylinders.**Types****ine centre**A 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.

**ine table**Sine table is used to measure angles of large workpieces.

**Compound sine table**It 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.

*Wikimedia Foundation.
2010.*

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