Sine bar PDF- Principle,Formula, Construction, Limitations&Factors: In the last session, we had discussed about Marking and Measuring Tools used in Engineering Workshop. Apart from that, a detailed article on Working of Vernier Caliper was also discussed. But in today’s article, we are going to study about Angular Measuring device called as Sine bar.

Note: Download Sine bar PDF at the end of the article. 

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.

Read:Fitting Workshop-Holding,Measuring,Marking, Cutting ,Finishing, Striking Tools

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

The detailed explanation is as follows…

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.

Sine bar - Principle,Formula,Construction,Limitations,Factors influencing the angle
Sine bar – Principle, Formula, Construction, Limitations, Factors influencing the angle

Explain the 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 Formula:

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

What are the 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:

  1. An error present in the length of the sine bar (? L)
  2. The difference in Dia of the rollers (d1 not equal to d2).
  3. Error present in the building of slip gauges.
  4. 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.

Sine bar Viva Questions:

1.What is the purpose of a sine bar?

Ans:Sine bar is used along with slip gauges for the precise angular measurement of any component.

2.Why there are holes in sine bar?

Ans:The holes are drilled into the body of sine bar to reduce the weight of it and also to facilitate easy handling.

3.Why is a sine bar not suitable for measuring angle above 45?

Ans:The sine bars become inaccurate as the angle exceeds 45° because the bar(product) is physically clumsy to hold at that position and even a slight error of the sine bar can cause large angular errors.

4.How is a sine bar specified?

Ans: For it,Read the construction of Sine bar.

5.What is the least count of slip gauge?

Ans: There is no possibility of Least count for slipgauges because they are represented interms of 0.5mm,1.0 mm and so on upto a desired value.


Note: PDF Download

You can download Sine bar PDF by the below links

Download PDF from Facebook Group:Education & Career, Mechanical Engineering

Download PDF from Telegram Group: Mechanical

Lessons for You:

Thermal Engineering

Theory of Machines

Non-Traditional Machining


Material Science Engineering



Forming Processes


Sheet Metal Operations

Elements of Mechanical Engineering

Workshop Manufacturing Practices 

Print Friendly, PDF & Email

Mohammed SHAFI

Mr. Mohammed Shafi is an Assistant Professor at Sreenidhi Institute of Science & Technology. By education, he is a Mechanical Engineer and expertise in CAD & CAM. Mechanical Students is his first...

Leave a comment

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.