Metrology and Inspection MCQ Quiz - Objective Question with Answer for Metrology and Inspection - Download Free PDF

Explanation:

Tool Maker’s Microscope:

• A Tool Maker’s Microscope is a precision instrument widely used in manufacturing and engineering industries for accurate measurements of small components, intricate profiles, and machined parts. This device is particularly valuable in quality control and design verification processes, ensuring that critical dimensions meet specified tolerances.
• The supporting column in a Tool Maker’s Microscope plays a vital role in its overall functionality. It is a structural component that contributes significantly to the stability and usability of the device.

Function of the Supporting Column:

• The supporting column in a Tool Maker’s Microscope is designed to provide a rigid and stable platform for securing the specimen or workpiece during measurement or inspection. By holding the specimen in place, the column ensures that the object remains stationary and aligned correctly relative to the microscope’s optical system. This stability is crucial for achieving high measurement accuracy and repeatability.
• Without a stable supporting column, even the slightest movement of the specimen could introduce errors in measurement or distort the observed image. The supporting column, therefore, directly contributes to the precision and reliability of the Tool Maker’s Microscope, making it an indispensable part of the instrument.

Key Features of the Supporting Column:

• It is made of robust and durable materials to withstand mechanical stresses and provide long-term stability.
• The column is designed to accommodate various specimen sizes and shapes, often featuring adjustable clamps or holders.
• It integrates seamlessly with other components of the microscope, such as the stage and optical system, ensuring proper alignment and functionality.

Concept:

The angle formed by a sine bar is calculated using the formula:

\( \sin(\theta) = \frac{h}{L} \), where:

h = height difference between rollers, L = distance between centers of rollers

Given:

h = 30 mm, L = 60 mm

Calculation:

\( \sin(\theta) = \frac{30}{60} = 0.5 \Rightarrow \theta = \sin^{-1}(0.5) = 30^\circ \)

Hence, the angle formed is: 30°

Explanation:

Pneumatic Comparators

• Pneumatic comparators are precision measuring instruments that use compressed air as the medium to perform dimensional measurements. These comparators are widely used in industrial and manufacturing settings where high precision and non-contact measurement are required. The principle of operation is based on the variation of air pressure or air flow, which is influenced by the dimension of the part being measured.

Presence of hysteresis

• Pneumatic comparators do NOT exhibit hysteresis. Hysteresis refers to the lag between the input and output in a system, often caused by friction, material deformation, or other factors in mechanical systems. Since pneumatic comparators rely on the flow of air and pressure changes to perform measurements, they do not involve mechanical contact or moving parts that could lead to hysteresis. This absence of hysteresis is one of the significant advantages of pneumatic comparators, as it ensures accurate and repeatable measurements without errors caused by mechanical lag.

Hysteresis is typically associated with systems that have elastic or mechanical components, such as springs, levers, or other mechanical arrangements. In the case of pneumatic comparators, the measurement principle is purely based on the flow and pressure of air, making them free from this phenomenon.

Additional InformationOption 1: High range of amplification

• Pneumatic comparators are known for their high range of amplification. They can amplify small dimensional variations significantly, making them highly sensitive and suitable for precision measurement tasks. This feature allows them to detect minute deviations in the dimensions of workpieces, which is essential in quality control processes.

Option 2: Non-contact inspection of work parts

• Pneumatic comparators perform non-contact inspection of work parts. Since the measurement is based on air flow and pressure, there is no need for the comparator to physically touch the workpiece. This non-contact feature is particularly advantageous for inspecting delicate or soft materials, as it prevents damage or deformation during the measurement process.

Option 3: No wearing of parts

• One of the key advantages of pneumatic comparators is the absence of mechanical contact between the instrument and the workpiece. This eliminates wear and tear on the measuring components, ensuring a longer lifespan and consistent performance of the instrument. This feature also reduces maintenance requirements.

Explanation:

Autocollimator:

• An autocollimator is an optical instrument that is used to measure small angles with very high sensitivity.
• The autocollimator has a wide variety of applications including precision alignment, detection of angular movement, verification of angle standards, and angular monitoring over long periods.
• An autocollimator is essentially an infinity telescope and a collimator combined into one instrument.

Additional Information 

Types of Autocollimators:

1) Visual Autocollimator:

• In a visual autocollimator, the angle of tilt of the reflecting surface is measured by viewing a graduated scale through an eyepiece. As the focal length of the visual autocollimator increases, the angular resolution increases and the field of view decreases.

2) Digital Autocollimator:

• In a digital autocollimator, the micrometer adjustment is provided for the setting but the coincidence of setting graticule and the target image is detected photo-electrically.
• This autocollimator is used in the lab.
• It has very high precision, provides real-time measurements, and is very user friendly.

Applications of Autocollimator:

1. Checking the straightness of machine tool slideways.
2. Measuring very small angles.
3. Checking parallelism.
4. Checking squareness of column to base.
5. Checking the flatness of bed plates and surface tables.
6. Measuring very small displacements.
7. Checking small linear displacements.

Advantages of Autocollimators:

1. It has very high accuracy.
2. It can measure wide range angle.
3. It is very easy to set up and operate.
4. Calibration traceable to international standards.
5. It can be used to see the result visually or electronically i.e on a computer screen.
6. Wide range of accessories and levels available.

Disadvantages of Autocollimator:

1. Maintenance is required regularly.
2. It is time-consuming.
3. It requires sample cutting and processing for tracing by the detector.

Explanation:

The Vernier bevel protractor is a precision instrument meant for measuring angles to an accuracy of 5 minutes i.e. (1/12)° i.e. 12th part of 1°.

Uses:

• Apart from being used for measuring angles, vernier bevel protractor is also used for setting work holding devices on machine tools, work tables etc

• It is used to measure the acute as well as obtuse angles.
• For setting work-holding devices to angles on machine tools, work tables etc.

Concept:

• The Vernier principle states that two different scales are constructed on a single known length of line and the difference between them is taken for fine measurements.

Determining the least count of Vernier callipers:

In the Vernier calliper shown in Fig 

Calculation:

Given:

One main scale division (MSD) = 0.5 mm

24 divisions of main scale = 24 × 0.5 = 12 

One Vernier scale division (VSD) = 12/25 mm 

Least count = 1 MSD - 1 VSD

The GO plug gauge is the size of the low limit of the hole while the NOT GO plug gauge corresponds to the high limit of the hole.

GO gauges which constantly rub against the surface of the parts in the inspection are subjected to wear and lose their initial size. The size of go plug gauge is reduced. To increase the service life of gauges wears allowance is added to the go gauge in the direction opposite to wear. Wear allowance is usually taken as 5% of the work tolerance.

Explanation:

Fit is a relationship that exists between two mating parts, a hole, and a shaft, with respect to their dimensional difference before assembly.

There are three types of fits.

Transition fit: It may sometimes provide clearance and sometimes interference. Here the tolerance zones of the hole and shaft will overlap each other.

Examples: Tight fit and push-fit, wringing fit, 

Clearance fit: Clearance is the difference between the size of the hole and the size of the shaft which is always positive. Here the tolerance zone of the hole will be above the tolerance zone of the shaft.

Examples: Slide fit, easy sliding fit, running fit, slack running fit, and loose running fit.

Interference fit: Interference is the difference between the size of the hole and the size of the shaft which is always negative i.e. shaft is always larger than the hole size. Here, the tolerance zone of the hole will be below the tolerance zone of the shaft.

Examples: Press fit, Shrink fit, heavy drive fit, and light drive fit, selective fit, Snap-fit, Force fit

Explanation:

Zero error

• When the fixed jaw and sliding jaw are closed, but the zero on the Vernier scale coincides with zero on the main scale. Then the Vernier calliper does not have zero error.

• When the fixed jaw and sliding jaw are closed, but the zero on the vernier scale does not coincide with zero on the main scale. Then the vernier calliper said to have zero error.

There are two types of error

1. Positive error
2. Negative error

Positive zero error

• Positive zero error occurs if zero on the vernier scale lies on right side of zero on the main scale.
• If the error is positive, the correction is negative.

Negative zero error

• A negative zero error occurs if zero on the vernier scale lies on the left side of zero on the main scale.
• If the error is negative, the correction is positive.

Important Points

Zero error is always subtracted from the observed readings.  

Explanation:

A hermaphrodite caliper is a tool used to layout lines that are parallel with the edges of the workpiece. It can also be used to locate the center of cylindrical shaped workplaces.

Explanation:-

The surface roughness on a drawing is represented by triangles.

Surface texture or roughness representation

The basic symbol consists of two legs of unequal length inclined at approximately 60° to the line representing the considered surface.

The symbol must be represented by a thin line.

The value of roughness is added to the symbols.

1. Roughness ‘a’ obtained by any production process.

2. Roughness ‘a’ obtained by machining.

3. Roughness ‘a’ obtained without removal of material.

If it is necessary to impose maximum and minimum limits of surface roughness, both values are indicated. a1 = Maximum limit; a2 = Minimum limit

Explanation:

In this capital letter H denotes hole and small letter g denotes shaft. This combination H7-g6 denotes the clearance fit. It can be seen in the table below the various types of fit according to the hole shaft system.

Explanation:

The Vernier principle states that two different scales are constructed on a single known length of line and the difference between them is taken for fine measurements.

Determining the least count of Vernier callipers:

In the Vernier calliper shown in Fig the main scale divisions (9 mm) are divided into 10 equal parts in the Vernier scale. i.e.

Least count = 1 MSD - 1 VSD

Calculation:

Given:

10 Main Scale Division (MSD) = 10 mm, 1MSD = 1 mm

10 Vernier Scale Division (VSD) = 9 mm, 1VSD = 0.9 mm

Least count = 1 MSD - 1 VSD

= 1 mm - 0.9 mm = 0.1 mm

The difference between one MSD and one VSD = 0.1 mm

Alternate Method
One main scale division (MSD) = 1 mm

One vernier scale division (VSD) = 9/10 mm

Least count = 1 MSD - 1 VSD = 1 mm - 9/10 mm

= 0.1 mm

The difference between one MSD and one VSD = 0.1

Explanation:

• This is generally used to measure the small displacement of spindles.
• It is having a sensitive gauging head with a high-quality dial indicator mounted on the sturdy column as shown in the above figure.
• This consists of fixed block A & movable block B which are coupled together with the help of slip gauges at the middle portion.

• Sigma comparator → used to measure the roughness of the surface
• The optical comparator → used for a wide range of dimensional inspection applications
• The electric comparator → used to compare the dimensions of a given working component with the actual working standard.

Concept:

The surface roughness on a drawing is represented by triangles.

Surface texture or roughness representation:

• The basic symbol consists of two legs of unequal length inclined at approximately 60° to the line representing the considered surface.
• The symbol must be represented by a thin line.

• The value of roughness is added to the symbols.

1. Roughness ‘a’ obtained by any production process

2. Roughness ‘a’ obtained by machining

3. Roughness ‘a’ obtained without removal of material

If it is necessary to impose maximum and minimum limits of surface roughness, both values are indicated. a₁ = Maximum limit; a₂ = Minimum limit