PROTRACTORS, BEVEL & UNIVERSAL

A bevel protractor is a graduated circular protractor with one pivoted arm used for measuring or marking off angles. With vernier scales attached to give more precise readings. Called a universal bevel protractor, the universal bevel protractor has wide application in architectural and mechanical drawing& marking out for toolmaking. The universal bevel protractor, 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 universal 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.

On the universal bevel protractor, since the spaces, both on the main scale and the Vernier scale, are numbered both to the right and to the left from zero, any angle can be measured. The readings on the universal bevel protractor can be taken either to the right or to the left, according to the direction in which the zero on the main scale is moved.

Reading the Vernier scale:

The bevel protractor Vernier scale may have graduations of 5′ (minutes) or 1/12°. Each space on the Vernier scale is 5′ less than two spaces on the main scale of the universal bevel protractor. Twenty four spaces on the Vernier scale equal in extreme length twenty three double degrees. Thus the difference between the space occupied by 2° on a main scale and the space of the Vernier scale is equal to one twenty-fourth of 2°, or 5′.

Read off directly from the main scale on the universal bevel protractor, the number of whole degrees between 0 on this scale and the 0 of the Vernier scale. Then count, in the same direction, the number of spaces from the zero on the Vernier scale to a line that coincides with a line on the main scale; multiply this number by 5 and the product will be the number of minutes to be added to the whole number of degrees.

For example: Zero on the vernier scale has moved 28 whole degrees to the right of the 0 on the main scale and the 3rd line on the vernier scale coincides with a line upon the main scale as indicated. Multiplying 3 by 5, the product, 15, is the number of minutes to be added to the whole number of degrees, thus indicating a setting of 28 degrees and 15 minutes.

The universal bevel protractor sounds confusing, though very easy once applied!!

Miracle Point protractor is ideal for marking out top centre of round bar ,etc. The vee is magnetised, then simply centre punch the top. The Miracle Point protractor also easy to set up work in the milling machine on an angle.