Bevel protractor

What is bevel protractor ?

A bevel protractor is a graduated circular protractor with one pivoted arm used for measuring or marking off angles. Sometimes Vernier scales are attached to give more precise readings. It has wide application in architectural and mechanical drawing, although its use is decreasing with the availability of modern drawing software or CAD.

Universal bevel protractors are also used by toolmakers, as they measure angles by mechanical contact they are classed as mechanical protractors.

The bevel protractor is used to establish and test angles to very close tolerances. It reads to 5 minutes or 1/12° and can measure any angle from 0° to 360°.

The bevel protractor consists of a beam, a graduated dial and a blade which is connected to a swivel plate (with Vernier scale) by thumb nut and clamp. When the edges of the beam and blade are parallel, a small mark on the swivel plate coincides with the zero line on the graduated dial. To measure an angle between the beam and the blade of 90° or less, the reading may be obtained direct from the graduation number on the dial indicated by the mark on the swivel plate. To measure an angle of over 90°, subtract the number of degrees as indicated on the dial from 180°, as the dial is graduated from opposite zero marks to 90° each way.

How to use bevel protractor ?

Step 1

Unscrew the large clamp on the front of the protractor. This loosens the blade, so that you can swivel it.

Step 2

Align the base of the protractor on one side of the angle, and them swivel the blade to form the other side of the angle. Tighten the large clamp.

Step 3

Find the zero on the vernier scale. The vernier scale is the smaller scale on the inside of the protractor.

Step 4

Read the number of degrees on the main scale, directly above the zero on the vernier scale. Say, for example, the zero on the vernier scale lines up with the 85 degree mark.

Step 5

Read the minutes on the vernier scale. The minutes are found by looking counterclockwise on the vernier scale, and noting the first place where the line on the vernier scale lines up (exactly) with the line on the main scale. For example, the first line to match up with a line on the main scale is 30. This is measured in minutes, so the measurement is 30 minutes.

Step 6

Add the degrees from Step 4 to the minutes from Step 5. In this example, the answer would be 85 degrees, 30 minutes.

Here is a video of how to use bevel protractor :

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