Sine Bar

What is a sine bar?

A sine bar is a precision measurement tool, which is basically a steel bar. The purpose is to measure angles for parts on finely ground or lapped steel. Most sine bars are no wider than 1 inch. They are also equipped with a precision cylinder that is at each end. Also, sine bars can be designed to have upper and lower ends, which allows the bars to be used in all directions.

When measuring parts, gauge blocks are used with a sine bar. The purpose of using gauge blocks is to hold the tool at an angle that forms an ABC right triangle. With the application of trigonometry, the formed angle in the triangle can be calculated. The name of sine gets its name from the formula ϴ = Asin(BC/AB).

The application of a sine bar is not as difficult as people think. However, it takes some time and patience to fully understand the science behind the device. For more information, please check the following details.


Similar product – sine plates

The design of sine plates is similar, but there are still some major differences. The structure of a sine plate is much wider and is connected by a hinge to a base plate. Sine blocks and sine plates are all used mainly as precision measurement tools, just like what a sine bar is used to do. However, under specific circumstances, sine plates can be used as fixturing devices.


Mathematic used in the devices

Trigonometry is the fundamental mathematic that is applied in the devices. Some have experience learning trigonometry would describe it is a hard concept to understand. However, the application is really simple, easy to understand, and incredibly useful. To form a precise angle, the application of trigonometry is essential. That is because, during the measuring work, there are usually two sides with a given length, let’s say A and B. By the definition of the formula ϴ = Asin(BC/AB), the angle between the two sides can be determined. Since the calculations are complicated when moving around the parts and using sine bars and sine plates, it is very important to know how to use the tools. The process takes practice and patience.


Practical uses

The purpose of sine bars and sine plates, as mentioned above, is actually identical. With gauge blocks, users can set the desired angle by using sine bars or sine plate. The combination also helps the object match a specific angle. When the sine bar (or sine plate) is placed just beneath the upper cylinder, a triangular prism is formed. The ABC right triangle serves as the basis when users are measuring the workpiece, and allows users to apply trigonometry formula ϴ = Asin(BC/AB) to derive the right angle. The design of the cylinders is to ensure that, during measurements, the length of the sides remains consistent. By doing this, the angle measured is reliable for further uses. Usually, the common center distance of each cylinder is between 6” to 10”. The design makes the whole measuring process more convenient and more efficient.


Accuracy in measurements

There are two main challenges in the measuring process: (1) measuring the angled parts, (2) measuring specific angles for different parts. With the help of sine bars and sine plates, the task becomes easier. However, to proficiently utilize the tools is not a simple mission, the process involves a great deal of calculation. For the new users, the measuring process with the tools can be difficult at first. That is why new users have to practice using them. These tools can be very useful and accurate, but it requires a certain amount of proficiency of the user.

According to the formula ϴ = Asin(BC/AB), when measuring low values, the sine value changes rapidly; but when at high values, the sine value changes in a slow way. Therefore, the accuracy of the result depends on the angle measured by the users. It is easy to that the accuracy is higher when working with smaller angles.

In conclusion, the accuracy of the tools is mathematically limited for two reasons: (1) When achieving the measurement, the numbers of elements involved in. (2) The proficiency of the user operating the tools. Still, sine bars and sine plates are great tools that simplify the measurement of complicated angled workpieces.

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