What is Bevel Protractor and How Does it Work?

Bevel protractor is an instrument that we use for measuring the angles of the objects. We see people using it with various objects that include jigs. Whereas, this occurs when we produce engineering/machine drawings.

Unlike a normal protractor, we adjust a bevel protractor for fitting an angle. Its base is present on the bottom side of the angle, whereas the blade moves to match the opposing side.

Various bevel protractors will have a vernier scale on them that normally exists underneath the degree scale.

What is Protractor?

A protractor is a measuring instrument, typically made of transparent plastic or glass, for measuring angles. Some protractors are simple half-discs. More advanced protractors, such as the bevel protractor, have one or two swinging arms, which can be used to help measure the angle.

Most protractors measure angles in degrees (°). Radian-scale protractors measure angles in radians. Most protractors are divided into 180 equal parts. Some precision protractors further divide degrees into arcminutes.

They are used for a variety of mechanical and engineering-related applications. One common use is in geometry lessons in schools.

What is Bevel Protractor?

A bevel protractor is a versatile measuring tool used to accurately determine angles, often in the realms of metalworking and woodworking. It features a pivoting arm with a graduated dial, allowing for precise angle measurements, making it indispensable in precision engineering and layout work.

A bevel protractor is a precision instrument comprising a circular scale marked with gradations and an arm, typically pigmented, which is employed for the precise measurement and construction of angles.

In the realm of geometry, protractors serve as spherical or semicircular tools designed to gauge angles or circles, with the standard unit of measurement being degrees.

Notably, the bevel protractor’s least count is often around 5 minutes (1/12th of a degree) or 0.0833 degrees.

Ancient half-disc protractors have existed for millennia, but more sophisticated versions, like the bevel protractor, incorporate one or two swinging arms that facilitate angle measurement.

This device boasts the capability to measure angles with a minimum increment of 5 minutes, making it suitable for determining the angles of various workpieces, including jigs. In some cases, the bevel protractor can be affixed to a Vernier scale to enhance measurement precision.

Bevel Protractor Range

The bevel protractor is useful for establishing and testing the angles to very close tolerances. It reads to 5 arcminutes and can also measure angles from 0 degrees to 360 degrees.

The bevel protractors have a beam, a graduated dial and a blade that has a connection with a swivel plate (with the vernier scale) by the thumb nut and the clamp. When the edges of the beam and the blade are parallel, a small mark on the swivel plate coincides with the 0 lines on the graduated dial.

To measure an angle between the beam and the blade having an angle of 90 degrees or less. The reading might come from the graduation number on the dial indicated by the mark present on the swivel plate.

For measuring an angle of over 90 degrees, we have to subtract the number of the degrees as indicated on the dial from 180 degrees. However, as the dial is graduated from opposite 0 marks to 90 degrees each way.

How to Use Bevel Protractor?

• Firstly, unscrew the large clamp on the front part of the protractor. It loosens the blade so that we can swivel it.
• Align the base of the protractor on one side of an angle, and then swivel the blade for making the other side of the angle.
• Tighten the huge clamp.
• Spot the zero on the vernier scale. The vernier scale is smaller on the inner side of the protractor.
• Read the number of the degrees present on the main scale, directly above the zero present on the vernier scale. For example, the zero that is on the vernier scale lines up with the mark of 85 degrees.

Working Principle of Vernier Bevel Protractor

As the Base Plate (Stock) acts as one of the working edges, and the other working edge will be the blade which is held on the circular plate. as you can see some of the sample positions of the Vernier bevel protractor are in action.

This Adjustment Blade can be rotated along with the circular plate on the main body. This means the vernier scale on the circular plate will be rotated on the Main scale which is graduated on the Main body as shown below.

The Vernier scale has 12 divisions on each side of the center zero. (It means there are 24 divisions on the vernier scale) The 12 divisions are denoted as 60 min on the vernier scale (Like this 15, 30, 45, 60). That means 12 division = 60 minutes

One division= 60/12 = 5 minute. On the Main scale, the same portion is represented as 23° (12 divisions on the vernier scale = 23° on the main scale). One division on the Vernier scale = 1.91666° = 1° 55′ (one degree 55 minutes).

As similar to the vernier caliper working principle as Zero on the vernier scale moves on the main scale. While taking a measurement, The Zero line on the vernier scale shows the reading on the main scale, called the main scale reading.

At somewhere the divisions on the vernier scale will coincide with the divisions on the Main scale. this reading is noted as the Vernier scale reading. With these values along with the least count of the Vernier bevel protractor, we can calculate the Reading.

Parts of Bevel Protractor

• Swivel plate: The swivel plate rotates over the dial. This swivel plate has a vernier scale which is integrated into it.
• Magnifying Glass: The swivel plate also has a magnifying glass present over the vernier scale. This magnifying glass is used to see the value of the angles in the main scale and the vernier scale more clearly.
• Vernier Scale: The vernier scale is fixed on the swivel plate and it moves with the swivel plate. Vernier Scale gives the remaining angle in minutes. There are 60 minutes in 1 degree. This vernier scale is added in the bevel protractor to increase the precision of angle measurement. In the center, the vernier scale has zero. The vernier scale has 12 divisions on both sides of the zero and each division is 5 minutes. So, there are 60 minutes on each side of zero on the vernier scale.
• Angle locking screw: This angle locking screw is used to lock the bevel protractor at a certain angle so that after locking angle can be measured without any disturbance. angle locking screw stops the swivel plate from rotating with respect to the dial or dial scale.
• Dial: This is the base of the bevel protractor over which the other parts are present. The main scale or the dial scale is marked over this dial.
• Dial scale: This dial scale is the main part of the bevel protractor. It contains the graduated scale of angle from a value of   0 degrees to 360 degrees. In this graduated scale, every tenth degree is numbered. These 360 degrees is divided into four divisions each of 90 degrees.
• Blade: This blade is made up of high carbon steel. This blade is a tapered blade. This blade is either 150 mm or 300 mm depending on the bevel protractor. When the blade is parallel to the stock the zero of the vernier scale matches with the zero of the main scale or the dial scale. One side of the blade has an edge of 45 degrees and the other side has an angle of 30 degrees so that 45 degrees and 30 degrees can be directly measured using these edges.
• Blade locking screw: A blade locking screw is available to lock the blade at a certain place. This screw is used when we set the required length of the blade with the surface of the workpiece.
• Stock: The stock is one of the contacting surfaces in the bevel protractor while measurement of angle. The stock is the integrated part of the dial. As it moves the dial also rotates with respect to the blade and the angle value is changed in the dial scale. The job or workpiece whose angle is to be measured is kept in contact with this stock on one side. The other side of the job surface whose angle is to be measured is kept in contact with the blade. The blade of the bevel protractor travels inside the slot present in the stock.

Types of Bevel Protractor

Bevel protractors come in different types, each tailored to specific measurement needs. The Universal Bevel Protractor features a circular scale and a vernier scale for versatile angle measurements.

Digital bevel protractors provide digital readouts for convenience and precision, while Optical Clinometer Protractors incorporate optical technology for angle measurement.

The various types of bevel protractors used are:

• Vernier bevel protractor
• Universal protractor
• Optical protractor

#1. Vernier Bevel Protractor.

A Vernier bevel protractor is a precision measuring instrument used to accurately measure and set angles. It consists of a main scale and a Vernier scale, which allows for precise angle measurements within minutes (1/60th of a degree).

It typically features a blade or blade-like arm with a Vernier scale attached, making it suitable for a wide range of angular measurements, including those in machining and engineering applications.

#2. Universal Protractor.

A universal protractor, also known as a universal bevel protractor, is a versatile measuring tool designed to measure and set angles in various planes, including horizontal and vertical.

It usually consists of two arms, one of which can rotate around the base, allowing measurements in different directions. Universal protractors often have vernier scales or digital readouts for high precision and are commonly used in mechanical and construction fields.

#3. Optical Protractor.

An optical protractor is an advanced instrument used for highly precise angle measurements. It employs optical principles, such as interference patterns or optical gratings, to measure angles with exceptional accuracy.

Optical protractors are often used in fields like optics, astronomy, and precision engineering, where precise angular measurements are critical. They provide non-contact measurements and are suitable for both small and large angles.

Advantages Of Bevel Protractor

• It can measure angle very precisely up to 5 arcminutes and can measure angle up to 360 degrees.
• It gives a very accurate measurement.
• It is used to establish and test to-bear angles in very close tolerance.

Applications of Bevel Protractor

• Bevel Protractor is used to check V Blocks.
• It is used to check the inside beveled face of the ground surface.
• It is also used for measuring acute angles.

FAQs.