Sine Bar

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

It consists of a hardened, precision ground body with two precision ground cylinders fixed at each end, the rollers are positioned at a precise distance and the top of the bar is parallel to the center line of the rollers. The dimension between the two rollers is chosen to be a whole number (for ease of later calculations) and forms the wiktionary:hypotenuse of a triangle when in use. The image shows a 10" and a 100mm sine bar.

When a sine bar is placed on a level surface the top edge will be parallel with the base. 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 trigonometric function#Right triangle definitions.

The hypotenuse is a constant dimension — (100mm or 10" in the examples shown).
The height is obtained from the dimension between the bottom of one roller and the tables surface.
The angle is calculated by using the Sine rule. $\sin \left(Angle^\circ\right) = {opposite \over hypotenuse}$

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


Home Articles Construction Tools Woodworking Store Tools Furniture Bathroom Flooring	Sine Bar A sine bar is a tool used to measure angles in metalworking. It consists of a hardened, precision ground body with two precision ground cylinders fixed at each end, the rollers are positioned at a precise distance and the top of the bar is parallel to the center line of the rollers. The dimension between the two rollers is chosen to be a whole number (for ease of later calculations) and forms the wiktionary:hypotenuse of a triangle when in use. The image shows a 10" and a 100mm sine bar. When a sine bar is placed on a level surface the top edge will be parallel with the base. 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 trigonometric function#Right triangle definitions. The hypotenuse is a constant dimension — (100mm or 10" in the examples shown). The height is obtained from the dimension between the bottom of one roller and the tables surface. The angle is calculated by using the Sine rule. $\sin \left(Angle^\circ\right) = {opposite \over hypotenuse}$ Angles may be measured or set with this tool. For precision measurements where the bar must be set at an angle, the use of gauge blocks are traditionally used.
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