3773 -workshop practice

WORKSHOP PRACTICE
LAB No. 2
Measuring Tools

Today’s LAB
 Measuring Tools
 Vernier Caliper
 Micrometer
 SWG

Measurement
 Measurement means to compare something
with standard.
 E.g. measuring length of a wire, diameter of a
cylinder, depth of any object.
 The SI unit of length is meter (base unit).
 Its multiples and sub-multiples are given in
the table.

Meter and its sub-multiples
Prefix Symbol
Relationship with
Meter (base unit)
meter m 1m = 1 m
deci dm 1dm = 10-1
m
centi cm 1cm = 10-2
m
milli mm 1mm = 10-3
m
micro µm 1 µm = 10-6
m
nano nm 1nm = 10-9
m
pico pm 1pm = 10-12
m

Meter and its multiples
Prefix Symbol
Relationship with
meter
deca da 1 dam = 101
m
hecto h 1 hm = 102
m
kilo k 1 km = 103
m
mega M 1 Mm = 106
m
giga G 1 Gm = 109
m

Measuring Tools
 Vernier caliper
 Vernier caliper is a measuring device used to measure
precise increments between two points.
 Micrometer
 Micrometer is a measuring device used for precisely
measuring thickness, inner and outer diameter, depth of
slots.
 SWG
 A gauge for measuring the diameter of wire, usually
consisting of a long graduated plate with similar slots
along its edge.

Vernier caliper
 Function
 To measure smaller distances
 Can measure up to .001 inch or .01mm.
 Features
 Larger, lower jaws are designed to measure outer points
e.g. diameter of a rod.
 Top jaws are designed to measure inside points e.g. size of
a hole.
 A rod extends from the rear of the caliper and can be used
to measure the depth.

Structure of the Vernier caliper
 Main Scale
 Main scale is graduated in cm and mm.
 Vernier Scale
 It slides on the main scale.
 On Vernier scale 0.9cm is divided into 10 equal parts.
 Jaws
 Two inside jaws (Upper)
 Two outside jaws (Lower)

Least Count
 Least count (L.C) is the smallest reading we can
measure with the instrument.
 L.C = one main scale division – one
vernier scale division
L.C = 1mm – 0.09mm
L.C = 0.1mm = 0.01cm
 Least Count = Value of the smallest division on MS/
Total number of division on VS
L.C = 1mm / 10 = 0.1 cm / 10 = 0.01cm

How to use Vernier caliper?
• Close the jaws
• Calculate the least count
• Place the object between
the two jaws
• Record the position of zero
of Vernier scale on the Main
scale (3.2cm)
• Notice the reading of VS
which coincides with MS
reading (3rd
division in this
case)

Reading of the Instrument
 Reading of the instrument = MS div +
(coinciding VS div x L.C)
 = 3.2 + (3 x 0.01)
 = 3.2 + 0.03
 = 3.23 cm

To measure the depth
 A rod extends from the rear of the caliper and
can be used to measure the depth.
 Open the jaws of caliper and place the rod
inside hole of the object, such as the rod
reaches the inner most portion of the object.
 Read the Vernier caliper. (same procedure as
described in previous slides)

Micrometer
 Function
 Micrometer allows the measurement of the size of the body
i.e. thickness, depth, inner/outer diameter.
 Features
 Two jaws (one fixed, one movable)
 Spring loaded twisting handle
 Easy to use and more précised
 Can measure up to .001cm

Structure of Micrometer
 Jaws
 2 jaws (one fixed, one movable)
 Circular Scale
 Movable jaw is attached to a screw, scale on this screw is
called Circular scale.
 Either 50 or 100 divisions
 Linear Scale
 Horizontal Scale

Structure of Micrometer
 Frame
 The C-shaped body that holds the anvil and sleeve in constant relation to
each other.
 Anvil
 The jaw which remains stationary.
 Spindle
 The jaw which moves towards the anvil.
 Lock Nut
 A lever, one can tighten to hold the spindle stationary.
 Sleeve
 The stationary round part with the linear scale on it. (Main Scale)
 Thimble
 Thimble rotates around the sleeve.
 Ratchet Stop
 Device on end of handle that limits applied pressure by slipping at a
calibrated torque.

Pitch of Micrometer
 When the head of the micrometer rotate
through one rotation, called pitch of the
micrometer.
 The screw moves forward or backward 1mm
on the linear scale.
 Pitch of Micrometer = distance on linear
scale / one rotation
Pitch of Micrometer = 1/1 = 1mm

Least Count
 Least Count = Pitch of the Micrometer / Total
number of circular scale division
 Least Count = 1 / 100 = 0.01mm
= 0.001cm

How to use Micrometer?
• Thimble
– The thimble rotates around a
cylinder which is marked in
millimeters.
– The left-hand side of the
thimble has markings all
around it.
– The line labeled 0 is the
primary pointer.
• Close the jaws
• Calculate the least count
• Place the object between the
two jaws
• Record the position of main
scale where the two measuring
rods met.
• Note the position of the circular
scale which coincides with
main scale

Reading of the Instrument
 Reading of the instrument = MS div +
(coinciding CS div x L.C)
 = 8+ (12 x 0.01)
 = 8 + 0.120mm
 = 8.120 mm = 8120 µm

Standard Wire Gauge (SWG)
 A gauge for measuring the diameter of wire, usually
consisting of a disk having variously sized slots in its
periphery or a long graduated plate with similar slots
along its edge.
 A standardized system of wire sizes.
 Wires are manufactured to standard sizes and
labeled with their SWG.
 As the SWG increases the diameter decreases.

SWG
SWG No. Diameter (inches) Diameter (mm)
0 0.324 8.230
1 0.300 7.620
2 0.276 7.010
3 0.252 6.401
4 0.232 5.893
5 0.212 5.385

Lab Reports
 Last date of submission of Lab 1 & 2 is
Wednesday, 4th
November till 1: 00 p.m. in
Workshop lab.

3773 -workshop practice

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