Although CMM measuring machines took away many of the traditional use cases of the **sine bar**, It is still **the most accurate method to measure the angle** of a ground surface.

Likewise, the **sine vice** is still a very effective **holding device to grind an inclined plane at a precise angle **on a manual surface grinder.

## Sine Bar Calculator

**(The calculator can be used also for sine plates and sine vises)**

## Sine Bar Formulas

**(The below formulas are valid also for sine plates and sine vises)**

\( \large L = H \times \sin{\theta } \)

**Explanation:** The formulas are straightforward and are a result of the fact that the sine bar forms a right triangle:

- The Sine Bar length (L) is measured between the center of the cylinders and forms the triangle’s hypotenuse.
- The Sine Bar height (H) is the height of the stack of the gauge blocks placed under the cylinder and constitutes the triangle’s opposed leg.
- The angle (Theta) results from these two basic properties.

## Sine Bar Principales

### How does it work?

Sine bar is a simple yet very accurate method to measure the angle of a part. It is built from a precision ground plate sitting on two precision ground cylinders, where the distance between the cylinders is a known whole number. (like 5″ or 100 mm)

** You need a Sine bar from a reputable manufacturer that guarantees the device’s accuracy across the board to get a precise result. The overall accuracy is a combination of several factors:**

- The accuracy and uniformity of the two cylinders (C1 and C2).
- The exact distance between the two-cylinder centers (Usually equal a whole number like 5 inches or 100 mm).
- The flatness of the top surface (A)
- The parallelism between the top surface (A) and the theoretical plane connecting the cylinder center lines (L).
- The accuracy of the gauge block stack (H).

### Measuring the angle of a small component:

- Calculate the needed height of the gauge block stack to level the plane horizontaly.

- Check the parallelism of the top surface with a dial indicator.
- If it is not close enough to zero, add or decrease the height of the stack.
- Repeat this step until reaching zero (or near zero) parallelism.
- Measure the total gauge block stack height.
- L is known from the Sinebar model.
- Calculate the actual angle:

**Measuring the angle of a large size component:**

- L is known from the Sinebar model.
- Measure H1 & H2 with a Dial Height Gauge.
- Calculate the angle:

## Types of Sine bars

**Sine Bar**

Used to measure the angle of a flat area on a workpiece.

**Sine center**

This sub-type of a sine bar is used to measure the angle on cylindrical parts.

**Sine Plate**

A holding device used to hold a large workpiece at a precise angle to perform milling or grinding operations. The clamping of the components can be magnetic or mechanical.

**Sine Vice**

This sub-type of a sine plate holds small components at a precise angle for machining (usually surface grinding).