Bevel protractor
The universal bevel protractor is a precision instrument widely used in tool rooms and metrology
laboratories for measuring angles with an accuracy of 5 arcminutes (5'). Its construction includes
several key components that facilitate accurate angular measurements.
Components and Functionality
1. Base Plate (Stock): The base plate has a highly flat surface to ensure stable contact with the
workpiece being measured. It is critical for achieving accurate readings.
2. Adjustable Blade: This blade can swivel to align with the angle of the workpiece. It is locked
in place to maintain the set angle during measurement.
3. Graduated Dial: The dial features a main scale graduated in degrees, allowing for direct angle
readings. Each main scale division represents 1°, and the scale is divided into four quadrants,
each measuring 90°.
4. Vernier Scale: A stationary vernier scale is mounted near the dial, enabling measurements to
a least count of 5'. The vernier scale has 24 divisions corresponding to 46 divisions on the
main scale, allowing for precise readings.
5. Acute Angle Attachment: This optional attachment is used for measuring acute angles,
enhancing the versatility of the protractor.
Measurement Process
To measure an angle, the following steps are typically followed:
• Position the base plate on the workpiece.
• Adjust the blade to coincide with the angle of interest.
• Lock the blade in place and read the angle from the main scale and vernier scale.
Example of Reading
For instance, if the zeroth division of the vernier scale is just past the 10° mark on the main scale, and
the seventh division of the vernier scale coincides with a main scale division, the reading would be
10°35'.
Types of Bevel Protractors
Bevel protractors are classified into four types: A, B, C, and D. Types A and B include a vernier scale
for enhanced accuracy, while types C and D do not. Type A is equipped with both an acute angle
attachment and a fine adjustment device, whereas type B lacks these features.
Guidelines for Accurate Measurement
To ensure accurate measurements with a universal bevel protractor, consider the following
guidelines:
1. Clean the instrument thoroughly before use.
2. Ensure proper contact between the protractor and the workpiece.
3. Verify that the instrument is in a plane parallel to the angle being measured.
4. Avoid sliding the instrument over abrasive surfaces and do not over-tighten clamps.
5. Maintain the instrument by cleaning and lubricating it after use.
By adhering to these guidelines and understanding the protractor's components and functionality,
users can achieve precise angle measurements essential for various engineering and machining
applications.
