**The principle of Sine bar:** Sine bar is used to measure the angle of the given specimen accurately. It usually measures the angle of the specimen as well as locates the workpiece(specimen) properly to measure the angle of it.

Bevel Protractor measures the angle of the given specimen directly whereas Sine bar measures indirectly by the usage of Slip gauges.

## Sine bar – Diagram, Formula, Construction, Limitations, and Factors influencing the angle:

**Sine bar diagram:**

The Sine bar diagram was shown below and the parts of the sine bar are explained below in the Construction of sine bar tab.

**Construction of Sine bar:**

- The length of the sine bar is used for specifying a sine bar i.e. at 200mm,sine bar is nothing but the distance between the centers of the two rollers equal to 200 mm.
- The top and bottom surface of the sine bar must be parallel to the line joining to the center of the rollers.
- Holes are produced in the sine bar for reducing the weight of the sine bar so that handling of the sine bar will become easier.
- Only sine bar can’t be used for measurement of angles of a component, but the sine bar is always used in association with slip gauges or Height Gauge for measurement of the angles.

**Sine bar Formulae:**

The Formula for the sine bar is represented in terms of height of the slip gauges constructed from the ground(h) and the length of the sine bar i.e. the distance between the centers of two rollers and was represented below.

Sin(θ) = h/L |

**Limitations of Sine bar:**

- Any unknown projections present in the component will cause to induce errors in the angle measured.
- For the building of the slip gauges, there is no scientific approach available and it is to be built on the trial and error basis and it is a time-consuming process.
- During measurement of an angle by using sine bar, the length of the sine bar should be greater than or equal to a length of the component to be inspected.

Sin(**θ**) = h/L

- If the length of the component Inspected is very long then there is no sine bar available which is longer than the Component. In such cases, the sine bar will be used in association with Height Gauge for measurement of the angles.

Sin(θ) = (h2-h1)/L |

**Factors influencing the angle measured by using sine bar:**

- An error present in the length of the sine bar (
**𝛿**L) - The difference in Dia of the rollers (d1 not equal to d2).
- Error present in the building of slip gauges.
- Parallelism error between gauging surface and line joining to the center of the rollers.

The surface of the sine bar which is in contact with the component is called **the gauging surface**.

In general, sine bar is used for measurement of smaller angles only,but not for larger angles this is because of a small amount of error present in the sine bar which is causing to produce smaller amount of angular errors.

If it is used for measurement of smaller angles, a same small amount of error present in the sine bar is causing to produce a large amount of angular error during measurement of larger angles**.**

**Read:**

- 3 Types of Marking Out Tools used in Fitting – Engineering Workshop
- Work Holding Devices in Fitting -Engineering Workshop