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What is a Sine Plate?

N. Kalu
N. Kalu

A sine plate is a precision manufacturing tool used to measure angles of larger-sized industrial objects, typically automotive parts. The angles of these parts are usually difficult to measure due to their odd or bulky shape. To measure an angle using this piece of equipment, professionals use a sine plate chart of constants, gauge blocks, and measuring tape. Notable types of this tool include the magnetic sine plate and the compound sine plate.

This device consists of two steel plates that lie parallel to each other. These plates are propped up by two metal bars that are found on the opposite ends of the plates. The bars keep the plates apart at an equal distance. There are also two cylinders at each end, and the distance between the centers of these cylinders is carefully noted. This distance is used when measuring out an angle by acting as the hypotenuse of the formulated triangle.


In work settings, the bottom plate is strapped to the work table while the top plate is left hinged to one of the metal bars. Gauge blocks are then stacked up between the bottom plate and the other metal bar. The top plate serves to stabilize the object while the object is measured. It contains bolt holes so that an object can be secured to it.

To use a sine plate, the center distance of the tool and the angle that needs to be measured must be determined. This is done by using measuring tape. Next, a sine plate chart is used to figure out the setting constant. The constant is based on the center distance determined, the desired angle, and the inch measure of the device itself. Reference tables are easily found online to aid in setting constant calculations.

Once the setting constant is established, gauge blocks are stacked underneath one of the roll cylinders until their combined height is equal to the constant. Gauge blocks can be assembled to equal any height from 0.03 inches to 6 inches (0.08 centimeters to 15 centimeters). When the gauge blocks have been placed and the angle set, the tool is then locked to hold the device in place.

There are two important variations of this tool. A magnetic sine plate uses magnets to more effectively hold pieces steady, from thin sheets to large work pieces. Compound sine plates are used to set compound angles for complex designs that require angles in multiple planes.

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