Engineering Metrology Questions and Answers – Micrometers

1. Micrometer is a

  1. Hand-Held measuring instrument
  2. Toe-Held measuring instrument
  3. Pole-held Measuring instrument
  4. Any of the above

Answer.1. Hand-held measuring instrument

Explanation:-

The word ‘micrometer’ is known by two different meanings. The first is as a unit of measure, being one-thousandth of a millimeter. The second meaning is a hand-held measuring instrument using a screw-based mechanism.

 

2. What is the least count of a micrometer?

  1. 0.02 mm
  2. 0.01 mm
  3. 0.1 mm
  4. 0.2 mm

Answer.2. 0.01 mm

Explanation:-

The least count is the minimum measurement that a scale can measure. A meter ruler may have graduations at 1 mm division scale spacing or interval. A Vernier scale on a caliper may have a least count of 0.1 mm while a micrometer may have a least count of 0.01 mm.

 

3. A micrometer is based on the principle of

  1. Divide and Rule
  2. Divide and Multiply
  3. Rotation and Revolution
  4. Screw and Nut

Answer.4. Screw and Nut

Explanation:-

Principle of Micrometer:- A micrometer is based on the principle of screw and nut. When a screw is turned through one revolution, the nut advances by one pitch distance, i.e., one rotation of the screw corresponds to a linear movement of the distance equal to the pitch of the thread.

 

4. The least count of a micrometer can be calculated by the

  1. Total number of division on vernier scale/smallest division on the main scale
  2. Largest division on the main scale/Total number of division on vernier scale
  3. Smallest division on the main scale/Total number of division on vernier scale
  4. Total number of division on vernier scale/Largest division on the main scale

Answer.3. Smallest division on the main scale/Total number of division on vernier scale

Explanation:-

The least count of the micrometer can be calculated as

Least count = Smallest division on the main scale/Total number of division on the vernier scale

If the circumference of the micrometer screw is divided into n equal parts then its rotation of one division will cause the nut to advance through pitch/n length.

The minimum length that can be used to measure in such a case will be pitch/n and by increasing the number of divisions on the circumference, the accuracy of the instrument can be increased considerably.

If the screw has a pitch of 0.5 mm then after every rotation, the spindle travels axially by 0.5 mm and if the conical end of the thimble is divided by 50 divisions, the rotation of the thimble of one division on the micrometer scale will cause the axial movement of the screw equal to 0.5/50 mm= 0.01 mm, which is the least count of the micrometer.

 

5. Which of the following is/are the parts of the micrometer

  1. Anvil
  2. Spindle
  3. Sleeve
  4. All of the above

Answer.4. All of the above

Explanation

The major components and markings of a micrometer include the frame, anvil, spindle, locknut, sleeve, sleeve numbers, sleeve long line, thimble marks, thimble, and ratchet. Micrometers are calibrated in either inch or metric graduations and are available in a range of sizes.

Frame:- The frame is the U-shaped part of a micrometer. It also represents the range of measurement. The larger the frame, the longer the range. Whereas, the smaller the frame, the shorter the range. It also provides support to the anvil and the spindle to secure the object. In addition, it’s commonly coated with plastic material to prevent the user’s body heat moves to the micrometer.

 

Anvil and spindle:-  The anvil of the micrometer is fixed and it is on the left-hand side of the frame. It should protrude at least 3 mm from the frame in order to permit the attachment of measuring wire support. There is a screwed spindle on the right-hand side of the frame and has threads of 0.5 mm pitch. The anvil and spindle are generally made of high grade tool steel. In some cases, the measuring faces of the anvil and spindle are tipped with tungsten carbide or some other suitable material. The diameter of the anvil and spindle should be equal.

Spindle clamp or lock nut:- A lock-nut is provided on the micrometer to lock the spindle when the micrometer is at its maximum reading. 4. Barrel and thimble. The barrel (also known as a sleeve) has a datum or reference line and fixed graduations. The thimble is a tubular cover fastened with the spindle and moves with the spindle. The bevelled edge of the thimble is divided into 50 equal parts and every fifth part is numbered.

Ratchet or friction stop:- The micrometer is provided with a ratchet or friction stop in order to enable satisfactory operation. When the spindle reaches near the work whose dimension is to be measured, then the ratchet is used to prevent excessive pressure on the spindle. The barrel, thimble, ratchet, and locking nut, for all sizes of micrometers, are made from wear-resistant steel.

Thimble:- It is a tubular cover fastened and integrated with a screwed spindle. When the thimble is rotated, the spindle moves in a forward or reverse axial direction, depending upon the direction of rotation. The conical edge of the spindle is divided into 50 equal parts. The multiples of 5 and 10 numbers are engraved on it and the thickness of graduations is between 0.15 to 0.20 mm.

Ratchet:- A ratchet is provided at the end of the thimble. It controls the pressure applied on the workpiece for accurate measurement and thereby avoids the excessive pressure being applied to the micrometer, thus maintaining the standard conditions of measurement. This arrangement is very important as a variation of finger efforts can create a difference of 0.04 to 0.05 mm of the measured readings.

 

6. Which of the following is incorrect about micrometer?

  1. Thimble and barrel should have a dull finish
  2. Total travel of the measuring spindle is called measuring range
  3. Graduated marked on the barrel should be 25-50 mm
  4. The screw has 10 or 20 threads per cm

Answer.3. Graduated marked on the barrel should be 25-50 mm

Explanation:-

A barrel has fixed engraved graduation marks on it and is provided with a satin-chromium finish or dull finish for glare-free reading. The graduations are above and below the reference line.

For all ranges of micrometers, the graduations marked on the barrel are only 0-25 mm.  First, note the minimum range of the outside micrometer. While measuring with a 50 to 75 mm micrometer, note it as 50 mm.

 

7. Which of the following option is true for the given statements?

Statement 1: There is a zero error in the micrometer

Statement 2:  Zero error in micrometer is checked by contacting the faces of the anvil and spindle

  1. Both statements -1 and statement – 2 are true and statement – 2 is the correct explanation of statement – 1
  2. Both statements -1 and statement – 2 are true but a statement – 2 is not the correct explanation of statement – 1
  3. Statement -1 is true and statement – 2 is false
  4. Statement -1 is false and statement – 2 is true

Answer.1. Both statements -1 and statement – 2 are true and statement – 2 is the correct explanation of statement – 1

Explanation:-

Before taking a micrometer reading, the range of the micrometer and zero error must be checked.

The zero error is checked by contacting the faces of the anvil and spindle for micrometers from 0-25 mm, and by placing a masterpiece of 25 mm between the anvil and spindle faces for micrometers from 25-50 mm.

When the zero on the thimble does not coincide with the zero on the reference line on the barrel, then there is a zero error in the micrometer.

 

8. The screw of a micrometer gauge advances by 1 mm when it is turned through two revolutions and the circular scale has 50 divisions. What should be the least count of the main scale?

  1. 0.5 mm
  2. 0.05 mm
  3. 5 mm
  4. 15 mm

Answer.1. 0.5

Explanation:-

The check the least count of the main scale first we have to calculate the pitch.

In 2 revolutions, screw advances through 1 mm

In 1 revolution, screw advances through 1/2 mm

Pitch – 1/2 = 0.5 mm

On giving one full rotation, the screw advances through 0.5 mm, hence the least count of the sleeve scale should not be more than 0.5 mm, otherwise, it would be difficult to know whether the screw has rotated through a fraction of a turn. The least count of the main scale should, therefore, be 0.5 mm ie., the pitch of the screw.

 

9. If the zero marks on the circular scale are below the reference line on the main scale, then the error is said to be _______

  1. Negative error
  2. Zero Error
  3. Positive Error
  4. Solid Error

Answer.3. Positive error

Explanation:-

When the zero marks on the circular scale are below the reference line of the main scale, then the error is said to be a positive zero error.

 

10. The maximum range of micrometer is limited to

  1. 0-25 mm
  2. 15-100 mm
  3. 100-300mm
  4. 450-500 mm

Answer.1. 0-25 mm

Explanation:-

The designated micrometer size is its largest opening, not its range.

Micrometers are available from a 0 to 25 mm range, to a 375 to 400 mm range, to even larger (eg, from a 0 to 0.5 in. range to a 19 to 20 in. range).  The maximum range of micrometers is limited to 500mm.Larger sizes can be obtained in both metric and inch.

Digital micrometers are available in 25, 50,75, and 100 mm sizes, with readouts to 0.002 mm (1, 2, 3, and 4 inches with 0.0002 in.).

Metric micrometers with vernier scales for discrimination of 0.002 mm are available up to 50 mm. (Up to 12 inches in 1 inch ranges with discrimination of 0.0001 in. are also available.)

 

11. What is the hardness of measuring faces of anvil and spindle?

  1. 600 HV
  2. 1000 HV
  3. 100 HV
  4. 800 HV

Answer.4. 800 HV

Explanation

Measuring faces of anvil and spindle has a hardness of about 800 HV  or 60– 65 HRC since they are in constant touch with metallic jobs being measured. If warranted, the faces are also tipped with tungsten carbide or similar material to prevent rapid wear. The anvil is ground and lapped to a high degree of accuracy. The material used for the thimble and ratchet should be wear-resistant steel

 

12. The measuring face of the micrometer is made up of

  1. Cast Iron
  2. Plastic
  3. Carbide or steel
  4. Chromium

Answer. 3. Carbide or Steel

Explanation

The most commonly used material for modern micrometer anvils is carbide material. Older micrometer anvils often were made entirely of steel, but this material did not hold up as well after extended use and most manufacturers have switched to carbide. A layer of carbide is located on the anvil face and helps to harden the surface resulting in higher accuracy and increased durability.

When comparing it to steel, carbide material has a number of advantages for use on a micrometer anvil. Carbide hardness and density are twice that of steel, its melting point is more than 1000°, and it has a thermal expansion much lower. All of these factors help to make a more durable and reliable tool.

 

13.  What is the total error in the micrometer?

  1. Positive and negative deviation from the zero point
  2. Error in parallelism
  3. Deviation from the measurement of a nominal dimension
  4. The maximum difference between ordinates of cumulative error

Answer.4. The maximum difference between ordinates of cumulative error

Explanation:-

With a screw micrometer, accuracy relies on the lead of the screw built into the micrometer barrel. Error in this type of micrometer tends to be cumulative and increases with the length of the spindle travel. This is one reason micrometers come in 1-inch (25 mm) measuring ranges.

The cumulative error is the deviation of measurement from a nominal dimension. It includes errors like thread errors, errors of measuring faces, etc. The maximum difference between ordinates of cumulative error is the total error.

 

14. How many divisions are graduated on thimble?

  1. 20
  2. 25
  3. 45
  4. 50

Answer.4. 50

Explanation:-

Thimble:- It is a tubular cover fastened and integrated with a screwed spindle. When the thimble is rotated, the spindle moves in a forward or reverse axial direction, depending upon the direction of rotation. The conical edge of the spindle is divided into 50 equal parts. The multiples of 5 and 10 numbers are engraved on it and the thickness of graduations is between 0.15 to 0.20 mm.

 

15.  When the zero marks on the circular scale is above the reference line of the main scale, then the error is said to be 

  1. Negative error
  2. Zero Error
  3. Positive Error
  4. Solid Error

Answer.1. Negative error

Explanation

When the zero marks on the circular scale are above the reference line of the main scale, then the error is said to be a negative zero error.

 

16.  Which of the following option is correct about the given statements about micrometer?

Statement 1: The anvil should not protrude from the frame.
Statement 2: An adjusting nut is present in the micrometer to compensate wear

  1. Only statement 1 is true
  2. Only statement 2 is true
  3. Both the statements are true
  4. Both the statements are false

Answer.2. Only statement 2 is true

Explanation:-

Anvil is fixed on the left side of the frame and has a diameter equal to that of the spindle. It protrudes at least 3 mm from the frame in order to permit the attachment of measuring wire support.

The lock nut is simply a quarter-turn nut that locks the spindle from turning. The sleeve contains the scale which is used to determine the measurement and the internal threads which allow the spindle to move. Always loosen the lock nut before turning the spindle. Failure to do this will cause undue wear and strain on the micrometer.

 

17. Which of the following is correct about micrometer?

  1. Plastic insulating grips are used on the frame
  2. Satin chrome finish increases the reading errors
  3. The barrel is the removable part of the frame
  4. A uniform and maximum measuring force is applied

Answer.3. Barrel is the removal part of the frame

Explanation:-

The frame is heavy and consequently has a high thermal mass, to prevent substantial heating up by the holding hand/fingers. It is often covered by insulating plastic plates which further reduce heat transference.

If one holds the frame long enough so that it heats up by 10 °C, then the increase in length of any 10 cm linear piece of steel is of magnitude 1/100 mm. For micrometers, this is their typical accuracy range.

A barrel has fixed engraved graduation marks on it and is provided with a satin-chromium finish or dull finish for glare-free reading. The graduations are above and below the reference line.

A uniform and minimum measuring force should be applied to reduce error in the micrometer.

The fixed parts of a micrometer are the frame, barrel, and anvil. The movable parts of a micrometer are the thimble and spindle.

 

18. In micrometer the rachet is used to

  1. Increase Pressure
  2. Increase accuracy
  3. Reduce pressure
  4. Both 2 and 3

Answer.4. Both 2 and 3

Explanation:-

The micrometer is provided with a ratchet or friction stop in order to enable satisfactory operation. When the spindle reaches near the work whose dimension is to be measured, then the ratchet is used to prevent excessive pressure on the spindle and assure accurate measurement.

 

19. Which of the following is/are the advantage of Micrometer

  1. Used for accurate measurement
  2. Used to measure thickness of gauge
  3. Use in Industrial purposes
  4. All of the above

Answer.4. All of the above

Explanation:-

Application of Micrometer

1. Micrometer is used to make more accurate measurements of dimensions of objects upto three decimal places of a centimeter.

2. In engineering industries thickness and diameters of objects are found out using a micrometer.

3. Micrometer is used to measure the thickness or gauge of various metal sheets, diameters of disks, cylindrical bars and plugs, the thickness of plywood used in carpentry.

 

20. The most common type of micrometer anvil are

  1. Flat
  2. Spherical
  3. Both 1 and 2
  4. None of the above

Answer.3. Both 1 and 2

Explanation

The most common type of anvil  in micrometer are

  1. Flat Anvil
  2. Spherical Anvil

Flat micrometer anvil

The flat micrometer anvil is the most commonly used type of micrometer anvil. Recommended for most uses, the flat micrometer anvil is a sensible purchase given how many different measurement tasks it can be used to complete. When using a flat anvil micrometer, you can gather measurement information quickly and directly, with very high resolution.

Spherical micrometer anvil

The spherical micrometer anvil is sometimes known as a ball micrometer anvil. The anvil on a spherical anvil micrometer is shaped in a curved formation, like a ball. This feature makes spherical anvil micrometers ideal for measuring thickness on rounded surfaces such as tubes.

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