# Metrology and Precision instruments - Mechanical Engineering Interview Questions

Metrology and Precision instruments Mechanical Engineering Interview Questions and answers for freshers and experienced on standard sizes, tolerance, caliper, micrometer, Gauges, template, Fits etc.

1. What is Nominal size?

The Nominal size of a dimension is the size by which it is referred to as a matter of convenience.

2. Define Actual size?
The Actual size of a dimension is its actual measured size.
3. What do you meant by Basic size?

The Basic size of a dimension is the size in relation to which all limits of variation are made.

4. Define Fits?

The relation between two mating parts with reference to ease the assembly is called Fit.

5. What is Limits?

Two extreme permissible sizes of a dimension are called Limits. The high limit for a dimension is the highest permissible size and the low limit is the lowest permissible size.

6. Define Tolerance?

The difference between the high and low limit of a size is called tolerance.

7. Define Allowance?

The intentional difference in the sizes of mating parts is called the Allowance.

8. What is the difference unilateral and bilateral system of tolerance? . Discuss the least count of a vernier caliper?

A smallest measurement that can be obtained on a vernier caliper is called the least count of a vernier caliper. Generally vernier calipers are available with 0.02mm least count in metric system and 0.001” in inch system.

9. Find out the least count of a vernier caliper when its main scale graduation is 49 mm and the vernier scale is divided in to 50 equal parts?

• Value of 1 main scale division = 1 mm
• Value of 50 vernier scale divisions = 49 mm
• Value of 1 vernier scale division = 49 x 50 mm or 0.98 mm
• Least count = 1 M.S.D – 1 V.S.D = 1 – 0.98 = 0.02 mm

10. What are the reasons behind false reading on vernier caliper while taking measurements?

• Vernier caliper may have defects.
• Tidy job piece or measuring faces of vernier caliper.
• Wrong way of holding the vernier caliper and unawareness of reading measurements.
• Taking measurements when the job on motion.
• Pressure variation of holding fingers.
• Temperature difference between the job and the vernier caliper.

11. What are the main merits of a vernier caliper over a micrometer?

• Vernier caliper is a multi purpose instrument, can be used to measure inside, outside, and depth as well, where a micrometer is not considered as multipurpose.
• The different size of a job can be measured with a single vernier caliper but numbers of micrometers are needed for different sizes of job.
• Vernier caliper is easy for taking measurements and simple working, where as a micrometer works with a principle of nut and bolt and quiet sensitive.
• The measurements can be taken easily by a vernier caliper than by a micrometer.

12. Name the various parts of a vernier caliper?

• Main scale or beam
• Fixed jaw
• Movable jaw
• Vernier scale
• Locking screws
• Inner measuring nibs
• Depth gauge.

13. What are the purposes of Vernier Height Gauge?

• For making parallel lines on the work piece to the accuracy of 0.02 mm in metric system and 0.001” in inch system.
• For comparing heights of finished work piece.

14. What is the use of of vernier Bevel Protractor?

Vernier Bevel Protractor is used to measure and check the angles of a job to the accuracy of 5’ (5 minutes).

15. What is the function of a Vernier Depth Gauge

A vernier depth gauge is used to measure and check the depth of blind holes, steps etc. to the accuracy of 0.02 mm 0.001”.

16. Why Micrometer carries a ratchet stop?

Ratchet stop supports to measure accurate reading applying uniform pressure on the measuring faces irrespective of operator’s skill and strength.

17. What are the reasons behind false reading on Micrometer while taking measurements?

• There is zero error in Micrometer.
• Dirty work piece or measuring faces of micrometer.
• Unengaged Ratchet stop.
• Taking measurement when the job on motion.
• Wrong way of holding Micrometer.
• Temperature variation between the work piece and the Micro meter.

18. Define Zero reading of a Micrometer?

Zero reading of a micrometer is the initial reading which may vary according to the size of the micrometer.

• Zero reading of 0-25 mm micrometer is 0
• Zero reading of 25-30 mm micrometer is 25 mm
• Zero reading of 50-75 mm micrometer is 50 mm etc

19. Specify the term Backlash of a micrometer?

Backlash is the lack of motion or lost motion of the spindle when the rotation of the thimble is changed the direction.

20. Mention the features of a Universal Bevel Protractor?

• Minimum reading is 5 minutes.
• Main scale and Vernier scale are on the same plane to eliminate the reading parallax.
• Fine adjustment of the blade insures the precision measuring and laying out of angle.
• Main parts are of hardened stainless steel to prevent rust.
• Combined with an attachment or Height gauge, a wide range of measurements is available.
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