Angular Measuring Instruments

I. Introduction

Angular measuring instruments play a crucial role in the field of metrology and mechanical measurements. These instruments are used to measure and determine angles accurately, which is essential in various industries such as manufacturing, construction, and engineering. In this topic, we will explore the fundamentals of angular measuring instruments and discuss different types of instruments used for angular measurements.

II. Sine Bar

A. Definition and Purpose

A sine bar is a precision measuring instrument used to measure angles with high accuracy. It consists of a hardened and ground bar with two cylindrical rollers at the ends. The purpose of a sine bar is to provide a reference surface for measuring angles using the principle of trigonometry.

B. Construction and Working Principle

A sine bar is typically made of high-quality steel and has a flat and parallel reference surface. The two cylindrical rollers are accurately placed at the ends of the bar. The working principle of a sine bar is based on the relationship between the length of the bar, the angle being measured, and the sine function.

C. Measurement Procedure

To measure an angle using a sine bar, the following steps are followed:

1. Clean the sine bar and the workpiece surface.
2. Place the workpiece on the reference surface of the sine bar.
3. Use a height gauge or a dial indicator to measure the height difference between the workpiece surface and the reference surface.
4. Calculate the angle using the formula: Angle = (Height difference / Length of sine bar) x 360 degrees.

D. Applications and Examples

Sine bars are commonly used in various applications, including:

• Setting up milling machines and lathes
• Checking the accuracy of angle plates and surface plates
• Measuring the taper angle of machine tools

E. Advantages and Disadvantages

Advantages of using a sine bar:

• High accuracy
• Simple and reliable
• Versatile

Disadvantages of using a sine bar:

• Limited to measuring small angles
• Requires additional tools for measurement

III. Angle Gauges

A. Definition and Purpose

Angle gauges are angular measuring instruments used to measure and verify the accuracy of angles. These gauges are available in various designs and configurations, allowing for precise angle measurements in different applications.

B. Types of Angle Gauges

There are several types of angle gauges, including:

1. Protractors: These are circular or semicircular tools with a graduated scale for measuring angles.
2. Bevel Protractors: These gauges consist of a blade and a graduated dial for measuring angles.
3. Universal Bevel Protractors: These gauges have a swiveling blade and a graduated dial for measuring angles in any plane.

C. Construction and Working Principle

Angle gauges are typically made of high-quality materials such as stainless steel or hardened steel. The working principle of angle gauges varies depending on the type of gauge. Protractors and bevel protractors use a reference surface and a graduated scale or dial to measure angles.

D. Measurement Procedure

The measurement procedure for angle gauges depends on the type of gauge being used. In general, the following steps are followed:

1. Place the angle gauge on the surface or workpiece.
2. Align the reference surface of the gauge with the angle being measured.
3. Read the angle measurement from the graduated scale or dial.

E. Applications and Examples

Angle gauges find applications in various industries, including:

• Carpentry and woodworking
• Metalworking and fabrication
• Engineering and construction

F. Advantages and Disadvantages

Advantages of using angle gauges:

• Wide range of measurement options
• Portable and easy to use
• Suitable for both small and large angles

Disadvantages of using angle gauges:

• Limited accuracy compared to other instruments
• May require additional tools for precise measurements

IV. Spirit Level

A. Definition and Purpose

A spirit level, also known as a bubble level or a carpenter's level, is a tool used to determine whether a surface is horizontal (level) or vertical (plumb). It consists of a glass tube filled with a liquid and an air bubble.

B. Types of Spirit Levels

There are several types of spirit levels, including:

1. Standard Spirit Levels: These levels have a single glass tube and are used for general leveling purposes.
2. Bull's Eye Levels: These levels have a circular glass tube with a central bubble and are used for leveling in all directions.
3. Torpedo Levels: These levels have a compact design and are used for leveling in tight spaces.

C. Construction and Working Principle

Spirit levels are typically made of aluminum or plastic. The glass tube is filled with a liquid, usually alcohol or oil, and an air bubble is trapped inside. The working principle of a spirit level is based on the principle of buoyancy. When the surface being measured is level, the air bubble will be centered in the glass tube.

D. Measurement Procedure

To use a spirit level, the following steps are followed:

1. Place the spirit level on the surface to be measured.
2. Adjust the position of the level until the air bubble is centered in the glass tube.
3. Ensure that the surface is level or plumb based on the position of the bubble.

E. Applications and Examples

Spirit levels are widely used in various industries and applications, including:

• Construction and carpentry
• Surveying and land leveling
• Installation of appliances and fixtures

F. Advantages and Disadvantages

Advantages of using a spirit level:

• Simple and easy to use
• Provides a visual indication of levelness
• Suitable for both horizontal and vertical measurements

Disadvantages of using a spirit level:

• Limited to measuring levelness and plumbness
• May require additional tools for precise measurements

V. Autocollimators

A. Definition and Purpose

Autocollimators are optical instruments used for the measurement of small angular displacements. These instruments are commonly used in precision engineering and metrology applications.

B. Construction and Working Principle

An autocollimator consists of a light source, a collimating lens, and a telescope. The light source emits a parallel beam of light, which is collimated by the lens. The collimated beam is then reflected by a mirror or a prism and observed through the telescope.

The working principle of an autocollimator is based on the measurement of the angular deviation of the reflected beam. When the reflected beam is parallel to the incident beam, the autocollimator indicates zero angular deviation.

C. Measurement Procedure

To measure angular displacements using an autocollimator, the following steps are followed:

1. Set up the autocollimator on a stable surface.
2. Align the autocollimator with the object or surface to be measured.
3. Observe the reflected beam through the telescope.
4. Adjust the position of the object or surface until the reflected beam is parallel to the incident beam.
5. Read the angular deviation from the autocollimator scale or digital display.

D. Applications and Examples

Autocollimators are used in various applications, including:

• Alignment of optical components
• Measurement of angular deflection in mechanical systems
• Calibration of angle measurement instruments

E. Advantages and Disadvantages

Advantages of using autocollimators:

• High accuracy and precision
• Non-contact measurement
• Suitable for measuring small angular displacements

Disadvantages of using autocollimators:

• Expensive compared to other angular measuring instruments
• Requires a stable setup and careful alignment

VI. Clinometers

A. Definition and Purpose

Clinometers, also known as inclinometers, are instruments used to measure the angle of inclination or slope of a surface. These instruments are commonly used in geology, surveying, and engineering applications.

B. Types of Clinometers

There are several types of clinometers, including:

1. Pendulum Clinometers: These clinometers use a pendulum or a weighted string to measure the angle of inclination.
2. Digital Clinometers: These clinometers use electronic sensors to measure the angle of inclination.
3. Bubble Clinometers: These clinometers have a liquid-filled tube with a bubble that indicates the angle of inclination.

C. Construction and Working Principle

Clinometers can be constructed using various materials and designs. The working principle of a clinometer depends on the type of clinometer being used. Pendulum clinometers use the principle of gravity and oscillation to measure the angle of inclination. Digital clinometers use electronic sensors, such as accelerometers, to measure the angle. Bubble clinometers use the principle of buoyancy to indicate the angle of inclination.

D. Measurement Procedure

To measure the angle of inclination using a clinometer, the following steps are followed:

1. Place the clinometer on the surface to be measured.
2. Align the clinometer with the direction of inclination.
3. Read the angle measurement from the scale or digital display.

E. Applications and Examples

Clinometers find applications in various fields, including:

• Geology and surveying
• Construction and engineering
• Outdoor activities such as hiking and camping

F. Advantages and Disadvantages

Advantages of using clinometers:

• Portable and easy to use
• Suitable for measuring angles in various environments
• Available in different types and designs

Disadvantages of using clinometers:

• Limited accuracy compared to other instruments
• Requires proper alignment and positioning

VII. Conclusion

In conclusion, angular measuring instruments are essential tools in metrology and mechanical measurements. Sine bars, angle gauges, spirit levels, autocollimators, and clinometers are some of the commonly used instruments for measuring angles accurately. Each instrument has its own construction, working principle, measurement procedure, and advantages and disadvantages. Understanding these instruments and their applications can greatly contribute to accurate and precise angle measurements in various industries and fields.

Summary

Angular measuring instruments are crucial in metrology and mechanical measurements. They include sine bars, angle gauges, spirit levels, autocollimators, and clinometers. Sine bars provide high accuracy measurements using the principle of trigonometry. Angle gauges come in various types and are used to measure and verify angles. Spirit levels determine if a surface is level or plumb. Autocollimators measure small angular displacements using optical principles. Clinometers measure the angle of inclination or slope of a surface. Each instrument has its own construction, working principle, measurement procedure, and advantages and disadvantages.

Analogy

Imagine you are a carpenter building a bookshelf. You need to ensure that the shelves are perfectly level. To do this, you use a spirit level, which is like a bubble-filled tube. When the bubble is centered, you know the shelf is level. Similarly, in metrology and mechanical measurements, angular measuring instruments like sine bars, angle gauges, and autocollimators help ensure accuracy and precision in measuring angles.