metrology core training

2. What is Nominal size?
The Nominal size of a dimension is the size by which it is referred to as a
matter of convenience.
Define Actual size?
The Actual size of a dimension is its actual measured size.
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.
Define Fits?
The relation between two mating parts with reference to ease the assembly
is called Fit.

3. 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.
Define Tolerance?
The difference between the high and low limit of a size is called tolerance.
Define Allowance?
The intentional difference in the sizes of mating parts is called the Allowance.
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.

4. 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?

11. 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.

12. 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.

13. Range of Vernier Calipers:

15. What are the purposes of Vernier Height Gauge?
Vernier height gauge is a special type of vernier instruments which is used to
measure heights of different engineering objects

17. 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".

19. 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).
The least count of bevel protractor is 5'.

24. 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

25. 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.

29. What is meant by zero error on a screw gauge?

30. Case (a): No zero-error
Case (b): Positive zero-error of 2 circular scale division. Positive zero-error correction
is done by subtracting the positive zero-error from the actual reading.
Case (c): Negative zero-error of 4 circular scale division. Negative zero-error
correction is done by adding the negative zero-error from the actual reading.

31. 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.
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.

32. 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.
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

33. What is backlash error ? Why is it caused ? How is it avoided ?
If by reversing the direction of rotation of the thimble, the tip of the screw does not
start moving in the opposite direction immediately but remains stationary for a part of
rotation; it is called backlash error.
Reason: It happens due to wear and tear of the screw threads.
To avoid the backlash error, while taking the measurements the screw should be
rotated in one direction only. If the direction of rotation of the screw needs to be
changed, then it should be stopped for a while and then rotated in the reverse
direction.

34. What is a Gear tooth Vernier caliper?
 A vernier gear tooth caliper consists of two vernier perpendicular to each
other.
 It is used for measuring the chordal thickness of a gear tooth at the pitch
circle of the gear.
 The horizontal vernier caliper is used for measuring the tooth thickness of a
gear.
 Its working is similar to an outside vernier caliper.
 The vertical vernier caliper is used for measuring the distance from the top
of a tooth (addendum circle) to the pitch circle of the gear.

37. What is dial indicator
Dial indicators are measuring devices designed expressly to measure relative
position. The primary parts of a dial indicator are the face or dial, the case, and the
plunger.
The plunger is a spring loaded part that can be depressed into the case causing the
dial to move

41. Lever Dial Gauge

42. State the uses of a Dial test indicator?
To check the parallelism of machined or ground surfaces.
To check the true rotation of round jobs.
To compare the dimensions of finished components.

44. Surface plates are flat and plane surface used as a horizontal reference
space for dimensional measurement,
What is a surface table used for?

45. A gauge is an important measuring device in the field of design
engineering. It is a device used to provide certain dimensional
information, according to a specified standard or system.
Some gauges are meant to measure the size of the object. But,
most gauges are mainly used to specify if the dimensions of the
measuring object are less or greater than defined standards that
are within the tolerance range.