In the engineering and manufacturing industry, accurate measurement of angles plays a crucial role. One of the most reliable tools for measuring the angular angles is the bevel protractor. It is used for measuring and setting angles with high precision. From machining components to checking the angular accuracy of surfaces, it plays a critical role in various industrial applications. Unlike a standard protractor, a bevel protractor is designed with a robust mechanism to deliver accurate angular readings, even down to minutes of a degree. A bevel protractor is a precision measuring instrument widely used in engineering, woodworking, and metalworking to accurately measure and set angles. This versatile tool is essential for tasks requiring precise angle measurements, such as the layout and machining of components, the alignment of machine tools, and the creation of intricate geometric shapes. As per the bevel protractor working principle, it operates on the concept of relative angular movement between a fixed base and a rotating blade. The angle formed between these blades is read off the graduated circular scale (or with the help of a vernier scale), giving precise angular measurements. 

This article shall explain all about Bevel Protractor. This topic in mechanical engineering is important for your upcoming examinations like SSC JE ME and RRB JE Mechanical Engineering.

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.

Fig 1: Bevel Protractor

• 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.

A bevel protractor comprises several essential components. The base serves as a stable foundation, while the vernier scale provides a means for accurate angle measurements, often marked in degrees, minutes, and seconds. Attached to the base is a movable blade or arm, which can be rotated to determine the angle between two surfaces.

The components comprising a bevel protractor include:

1. Swivel Plate

The swivel plate is a pivotal component of the bevel protractor, allowing it to rotate smoothly on the dial. This swivel plate also features an integrated vernier scale for precise angle measurements.

2. Magnifying Glass

A magnifying glass is incorporated into the swivel plate, enhancing the visibility of angle values on both the main and the vernier scales. It facilitates clear and accurate reading of angles.

3. Vernier Scale

The vernier scale is affixed to the swivel plate and moves along with it. It plays a critical role in providing minute angle measurements in minutes, with 60 minutes equaling 1 degree. The inclusion of the vernier scale significantly enhances the precision of angle measurement. The vernier scale centers on zero and consists of 12 divisions on each side, each representing 5 minutes. Thus, there are 60 minutes on either side of the zero mark.

4. Angle-Locking Screw

The angle-locking screw serves to secure the bevel protractor at a specific angle, ensuring stable and disturbance-free angle measurement. It prevents the swivel plate from rotating in relation to the dial or dial scale.

5. Dial

The dial forms the foundational base of the bevel protractor, serving as the platform for other integral components. It hosts the primary scale, also known as the dial scale.

6. Dial Scale

The dial scale is the heart of the bevel protractor, featuring a graduated angle measurement range from 0 to 360 degrees. The scale is marked at every tenth degree and is divided into four 90-degree segments.

7. Blade

The blade, typically crafted from high-carbon steel, is a thin, elongated component of the bevel protractor. Depending on the protractor model, its length varies, with options of either 150 mm or 300 mm. The blade aligns parallel to the stock, with its zero corresponding to the zero of the main or dial scale. The blade features one end set at 45 degrees and the other at 30 degrees, enabling direct measurement of these angles.

8. Blade-Lock Screw

The blade-lock screw is employed to secure the blade at a specific position, especially when determining the required blade length along the workpiece's surface.

9. Stock

When measuring angles, The stock is one of the contact surfaces in the bevel protractor. It is an integral part of the dial assembly and moves in relation to the blade, causing changes in the angle value displayed on the dial scale. During angle measurement, the workpiece to be assessed is placed in contact with the stock on one side, while the other side of the workpiece's surface aligns with the blade, which fits into a slot in the stock. This arrangement ensures accurate angle determination.

Bevel Protractor Working Principle

Bevel Protractor is a precise angle measurement tool used in the mechanical and civil engineering industries. It is useful for measuring the marking angles with a high degree of accuracy. The bevel protractor works on the principle of relative angular movement. It uses a graduated circular scale to read the angle between its base blade and adjustable blade. Understanding the working principle of a bevel protractor helps in using the instrument correctly and efficiently.

• To begin the angle measurement process with a bevel protractor, start by positioning the workpiece between the blade and the stock of the instrument. Ensure that one side of the surface being measured aligns with the blade while the other sides make contact with the stock.
• Once the workpiece is appropriately aligned with the blade and the blade itself is correctly positioned on the workpiece, secure the blade in place using a locking screw designed for this purpose. Subsequently, when the surface being measured is fully in contact with both the stock and the blade, lock the angle in place using angle-locking screws.
• Next, direct your attention to the main scale, seeking the values that align with the zero mark on the Vernier scale. The value read from the main scale provides the angle in degrees, with the precise angle on the main scale just before the zero point of the Vernier scale.
• To refine the measurement further, locate the line on the Vernier scale that aligns perfectly with a line on the main scale. Once you've identified this alignment, note the position of the line on the Vernier scale. Calculate the minutes by multiplying the position of this coinciding line on the Vernier scale by 5 (five).
• Finally, record the angle measured using the bevel protractor, specifying both degrees and minutes. This method ensures a highly accurate measurement of angles when employing a bevel protractor.

Bevel Protractor Range

• The bevel protractor is a precision instrument known for its remarkable ability to establish and assess angles, measuring down to 5 arcminutes. It offers a broad angle measurement range, spanning from 0 degrees to a full 360 degrees.
• Comprising a beam, a graduated dial, and a blade linked to a swivel plate via a thumb nut and clamp, the bevel protractor's key components enable precise angle determination. When the beam and blade align in parallel, a small indicator on the swivel plate coincides with the 0 reference lines on the graduated dial.
• To measure an angle of 90 degrees or less between the beam and the blade, one can read the graduation number on the dial corresponding to the mark on the swivel plate.
• For angles exceeding 90 degrees, the method involves subtracting the degree value indicated on the dial from 180 degrees. Notably, the dial is calibrated from both 0 marks to 90 degrees in opposite directions, accommodating the measurement of angles in all quadrants.

Bevel Protractor Diagram

A bevel protractor diagram represents the parts and working structure of this precision angular measuring tool. It helps to understand the layout and function of each component.A typical bevel protractor consists of a base blade and a protractor head. Vernier scale and others. The diagram is essential in workshops for showing how the bevel protractor measures angles between surfaces or machine parts. It also illustrates how angles can be read directly or through the vernier scale. Accurate interpretation of the diagram ensures proper usage in mechanical tasks.

Bevel protractor Least Count

A bevel protractor is a precision measuring tool used to measure angles accurately. It is commonly used in mechanical engineering, machining, metalworking, and inspection processes to check angular dimensions. One of the most important aspects of any measuring instrument is its least count. The bevel protractor least count is the smallest measurement that an instrument can reliably read or display. It depicts how precise the instrument is. For a bevel protractor, the least count defines how small an angle it can measure.

Example: If a bevel protractor has a least count of 5 minutes, it means the instrument can detect angle differences as small as 5 minutes (Where 1 degree = 60 minutes).

How to Calculate the Least Count of Bevel Protractor

The bevel protractor least count is the smallest angle that it can measure accurately. This is important in precision engineering work where tiny angular differences matter. Candidates can check the information below on the steps to calculate the least count of the bevel protractor. The standard formula for calculating the least count (LC) of any vernier-based instrument is:

Least Count (LC) = Value of 1 Main Scale Division (MSD) − Value of 1 Vernier Scale Division (VSD)

Where:

MSD = Value of one division on the main (degree) scale

VSD = Value of one division on the vernier scale

Given:

\(1 \mathrm{MSD}=1^{\circ}\)

\(12 VSD =11 MSD\)

Step 1: Convert 11° into minutes

\(11^{\circ}=11 \times 60=660 \text { minutes }\)

Step 2: Calculate the value of 1 VSD

\(1 \mathrm{VSD}=\frac{660 \text { minutes }}{12}=55 \text { minutes }\)

Step 3: Value of 1 MSD

\(1^{\circ}=60 \text { minutes }\)

Step 4: Apply Formula

\(\mathrm{LC}=60-55=5 \text { minutes }\)

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

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.

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.

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.

Bevel Protractor Advantages

The advantages of Bevel Protractor include:

• High accuracy in angle measurement.
• Easy to use and read.
• Durable construction for long-lasting use.
• Suitable for various industries and applications.
• Allows for precise alignment of machine tools and components.
• Versatile for measuring a wide range of angles.
• Useful in quality control and inspection processes.
• Supports precise layout and machining tasks.
• Essential for creating and verifying specific angles in woodworking and metalworking.

Bevel Protractors Disadvantages

Bevel protractors are precision measuring instruments commonly used in metrology and various machining and manufacturing applications. While they offer several advantages, they also have some disadvantages:

• Limited Range: Bevel protractors typically have a limited measurement range. Depending on the specific model, their range may be limited to 360 degrees or less. This can be a drawback when measuring angles that exceed the protractor's range.
• Limited Accuracy: The accuracy of a bevel protractor is influenced by the skill of the operator. Achieving high precision measurements requires a steady hand and careful alignment. Human error can affect the accuracy of the measurements.
• Parallax Error: This can lead to inaccurate angle readings. Some modern bevel protractors incorporate anti-parallax features to mitigate this issue.
• Cumbersome for Some Applications: Bevel protractors are not suitable for measuring angles in hard-to-reach or confined spaces. They can be relatively large and may not be practical for certain applications where space is limited.

Uses of Bevel Protractor

The applications of bevel protractor are:

• Measuring and setting precise angles in engineering and construction.
• Checking and aligning machine tool components.
• Creating geometric shapes with specific angles.
• Verifying the accuracy of angles in various workpieces.
• Assisting in the fabrication of jigs and fixtures.
• Conducting quality control inspections in manufacturing.
• Enabling angle measurements in metalworking and woodworking projects.
• Supporting architectural and mechanical drafting.
• Verifying the alignment of vehicle components, such as wheel alignment.
• Facilitating angle measurements in educational settings.

This current article delved into Bevel Protractor. We suggest that you appear in the SSC JE Mechanical mock tests and SSC JE ME Previous Years Papers. Also, get enrolled in the AE/JE Mechanical coaching to get a firm grip on the subject.

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