Sine bar

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A sine bar is a tool used to measure angles in metalworking.

10" and 100mm Sine bars
10" and 100mm Sine bars

It consists of a hardened, precision ground body with two precision ground cylinders fixed at each end. 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 hypotenuse 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 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 \right) = {opposite \over hypotenuse}

Angles may be measured or set with this tool. For precision measurements where the bar must be set at an angle, gauge blocks are traditionally used.

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 degree.

Sine table is used to measure angles of large workpieces

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.

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This article has been tagged since February 2007.


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