A sine bar is a precision measuring instrument used in metalworking and machining to measure angles very accurately or to set up a workpiece at a specific angle. It typically consists of a hardened, precision-ground steel bar with two cylindrical, precision-ground rollers of equal diameter fixed at each end. The distance between the centers of the two rollers is a standard length, usually 5 inches or 10 inches.
How a Sine Bar Works:
- Principle: The sine bar works on the principle of trigonometry, specifically the sine function. The angle is determined by the relationship between the height of the sine bar’s elevation and the distance between the centers of the rollers.
- Setting Up: To measure or set an angle, the sine bar is placed on a flat surface with one of the rollers elevated by a specific height using gauge blocks. The height of the elevation (opposite side) and the distance between the rollers (hypotenuse) allows the calculation of the sine of the angle.
- Formulas:
Uses:
- Angle Measurement: A sine bar is used to measure the angle of a surface by setting it on the workpiece and adjusting the height until the top surface is parallel to a reference plane.
- Angle Setup: It is also used to set a workpiece at a precise angle for machining operations.
Limitations:
- Limited Angle Range: Sine bars are generally accurate for angles up to about 45°. Beyond that, the accuracy decreases due to the increasing height required.
Sine bars are commonly used in tool rooms, inspection departments, and during the machining of precise components.