EXPERIMENT NO. 1 : MEASUREMENT WITH
SCALE AND VERNIER
CALIPERS
Measurement and
Metrology Lab
Structure
1.1
Introduction
Objectives
1.2
Instruments Used
1.3
Working Principle
1.4
Procedure
1.5
Precautions and Care of Instruments
1.1 INTRODUCTION
In this experiment, you will be introduced to vernier caliper for taking both inside and
outside measurement. It uses the vernier principle of measuring which was named after
its inventor, Pierre Vernier (1588-1637), a french mathematician. The vernier caliper
essentially consists of two steel rules and these can slide along each other.
Objectives
After performing this experiment, you should be able to
•
use the vernier caliper, and
•
read the measurement with vernier caliper.
1.2 INSTRUMENTS USED
(a)
Steel scale, 300 mm
(b)
Steel scale, 150 mm
(c)
Vernier caliper, size 150 mm, LC = 0.02 mm
(d)
Vernier caliper, size 300 mm, LC =0.02 mm
(e)
Surface plate, 450 mm × 450 mm
(f)
Magnetic base, 50 mm × 50 mm
(g)
Straight edge, 250 mm.
1.3 WORKING PRINCIPLE
The principle of vernier was first introduced by Pierre Vernier in 1631. A vernier scale
consists of a fixed scale having normal divisions like mm and another sliding scale
having slightly smaller division. The sliding scale slides along the main or fixed scale.
The accuracy of measurement depends upon the difference between one division of main
scale and one division of sliding scale. This difference is the least length that can be
measured by vernier scale and is called the least count (LC).
Least count = 1 main scale division – 1 vernier scale division. Suppose 50 vernier scale
division coincide with 49 divisions on main scale, and 1 MSD = 1mm.
5
Laboratory-IV
Then
1 VSD =
49
Division on main scale,
50
and
LC = 1 −
49
1
=
of MSD
50 50
Figure 1.1 shows the details of a vernier caliper. Figure 1.2 shows 25 divisions of vernier
24 1
=
coinciding with 24 divisions on main scale giving LC = 1 −
divisions and since
25 25
1
one division of main scale is 0.025 hence LC =
of main scale.
1000
Reading of Dia
Fine Adjustment Clamp
2
3
Vernier Scale
Not Shown
Dia
4
5
Fine Adjustment Screw
Sliding Member
Figure 1.1 : Vernier Caliper
1.4 PROCEDURE
(a)
Study the engineers scale, its main and subsidiary divisions and compare the
scale with a straight edge. Note the length of the scale, its minimum division
and observe the straightness.
(b)
Measure sample piece, read and record the reading in the Proforma
suggested.
(c)
Study the vernier caliper and its constructional details; Figure 1.1 gives the
important parts of the calipers.
(d)
Understand the vernier principle and see how the least count is calculated.
Calculate and check error if any.
(e)
Read the instrument for at least three random vernier positions.
(f)
Measure the samples at indicated places and record as per standard Proforma
(Figure 1.2).
Figure 1.2
6
Reading = 2 + 0.4 + 0.025 + 0.011
Measurement and
Metrology Lab
(2 large division on main scale
+ 4 small division on main scale
+ 1 smallest division on main scale
+ 11 division on vernier scale, each division = 1/1000).
Hence reading = 2.436.
Figure 1.3 : Some Details of Using Vernier Caliper
1.5 PRECAUTIONS AND CARE OF INSTRUMENTS
(a)
The end of the scale must never be set with edge of the part to be measured
because the end of the scale is usually worn out in an old scale.
(b)
The scale should never be laid flat on the part to be measured because by
doing so the graduation of the scale are not in direct contact with the surface
of the part.
(c)
Check if steel rule ends are worn round or unsquare before using.
(d)
All instruments should be thoroughly cleaned, covered with mobil oil and
put in dust free covers.
(e)
When putting any instrument on table it should not be put violently or with
a jerk.
(f)
While measuring length standards by above instrument error of parallax or
zero error should be avoided.
(g)
In vernier calipers, there should be no play between sliding jaw and the
fixed scale.
7
Laboratory-IV
EXPERIMENT NO. 2 : MEASUREMENT WITH
MICROMETERS – INTERNAL
AND EXTERNAL
Structure
2.1
Introduction
Objectives
2.2
Instruments Used
2.3
Working Principle
2.4
Procedure
2.5
Precautions and Care of Instruments
2.1 INTRODUCTION
Micrometer is one of the most widely used precision instruments. The instrument was
invented and named by William Gascirgne. The name was derived from Greek work
Mikros that means small. Micrometer is a widely used device in mechanical engineering
for precisely measuring thickness of blocks, outer and inner diameters of shaft and depths
of slots. Micrometers have several advantages over other types of measuring instruments.
They are easy to use and their readouts are consistent. There are three types of
micrometers based on their application :
•
External micrometer
•
Internal micrometer
•
Depth micrometer
It is primarily used to measure external dimension like diameter of shaft, thickness of
parts etc. to an accuracy of 0.01 mm. In this experiment, you will be introduced to the
measurement of internal and external dimensions with the help of micrometer.
Objectives
After performing this experiment, you should be able to
•
measure internal dimensions with the help of micrometers, and
•
measure external dimensions with the help of micrometers.
2.2 INSTRUMENTS USED
External Micrometers
Least count = 0.1 mm, 0.001 mm (vernier type)
Measuring range as below :
(a)
0-25 mm
(b)
25-50 mm
(c)
50-75 mm
(d)
75-100 mm
Internal Micrometres
8
Measurement and
Metrology Lab
Least count = 0.01 mm
(a)
Calliper Type (5 mm-25 mm range)
(b)
Internal micrometer with different extension rods. 25 mm upwards
measuring range.
2.3 WORKING PRINCIPLE
The limits of accuracy specified on certain component involves measuring to 0.01 mm or
0.001 mm or even to finer limits which cannot be carried out by ordinary steel rule. Such
measurements can be made with the help of micrometer.
The micrometer consists of a precision screw in a nut. The outer cylindrical surface of
nut is marked with normal scale with one division equal to say 1/2 mm. The circular edge
of the screw which advances on the linear scale carries fine divisions say 50. If the screw
is given one full rotation it advances by one division of linear scale which is achieved by
having the pitch of the screw equal to 1/2 mm.
The least count of the micrometer is the advance of screw when screw rotates by one
division on circular scale. This is the least count. Least count for a micrometer of
1
= 0.01 mm .
1/2 mm pitch and 50 divisions on circular scale will be =
2 × 50
Anvil
B
Measuring Range A to B
A
Spindle Clamp
Fiducial Line
6
Measuring
Faces
Spindle
5
5
0
4.5
Barrel
Thimble
Friction or
Ratchet Drive
Frame
Figure 2.1 : Micrometer
0
10
15
Figure 2.2 : Inside Micrometer Caliper
Figure 2.3
Read 0.2 + 0.075 + 0.010 = 0.285
In the top figure as 10 Dn on thimble coincides with fiducial line. In the figure below
note that only Dn 3 on thimble closely coincides with the line parallel to fiducial line on
the barrel or sleeve. Hence read 0.2 + 0.050 + 0.02 + 0.0003 = 0.2703.
9
Laboratory-IV
2.4 PROCEDURE
(a)
Study the main elements of external/internal micrometer : U-frame, barrel,
thimble, locknut, and ratchet.
(b)
Calculate the least count and note range of measurement of the instrument.
(c)
Read off any three positions of the main and subsidiary scale.
(d)
Measure the given piece and record as per standard Proforma.
2.5 PRECAUTIONS AND CARE OF INSTRUMENTS
10
(a)
The part to be measured must be held in left hand and micrometer in right
hand. The way for holding the micrometer is to place the small finger and
adjoining finger in the U-shaped frame. The forefingers and thimble are
placed near the thimble to rotate it and middle finger supports the
micrometer while holding.
(b)
The micrometer should be wiped clean and free from oil, dirt, dust and grit.
(c)
Clean the measuring surfaces of anvil and spindle for every measurement.
(d)
Check for zero reading. If there is no ratchet, use the pressure on thimble for
checking zero error.
(e)
The anvil and spindle measuring surfaces should be flat and square to the
anvil and spindles respectively.
(f)
When micrometer feels gummy, dust ribbon and thimble fail to turn freely,
take the micrometer apart and thoroughly wash each component free from
dirt and then assemble. Stickiness may be due to damaged threads or due to
warping of frame or spindle.
(g)
Never leave the micrometer stored away with the spindle clamped down on
empty anvil as electrolytic action takes place on contacting surfaces and
measuring surfaces get corroded.
(h)
It is better to hold the micrometer anvil stationary and firmly against the
work in one hand and take care of gauging pressure and locating the correct
position of spindle by the movement of fingers of the other hand causing
rotation of the spindle.
EXPERIMENT NO. 3 : MEASUREMENT WITH
HEIGHT AND DEPTH GAUGE
Measurement and
Metrology Lab
Structure
3.1
Introduction
Objectives
3.2
Instruments Used
3.3
Working Principle
3.4
Procedure
3.5
Precautions and Care of Instruments
3.1 INTRODUCTION
Gauges are the tools which are used the checking the size, shape and relative positions of
various parts. Gauges do not indicate the actual value of the impacted dimensions on the
work. Gauges are, therefore, understood to be single-size fixed-type measuring tools. In
this experiment, you will be introduced to the height gauge as well as the depth gauge.
Objectives
After performing this experiment, you should be able to
•
understand the fundamental of the gauges and their classifications, and
•
explain the working principle of height and depth gauge.
3.2 INSTRUMENTS USED
(a)
Height Gauge, 300 mm range, least count 0.02 mm
(b)
Depth Gauge, 100 mm range, least count 0.02 mm
(c)
Surface Plate, 450 × 450 mm, Grade I
(d)
V-Blocks, 30 × 30 × 50 mm.
3.3 WORKING PRINCIPLE
The principle of working of height gauge is same as that of vernier calipers. It is the same
simple arrangement as vernier caliper using a fixed scale and sliding scale to obtain
measurement of higher accuracy, than can be obtained by an ordinary steel scale. It relies
on the difference between two calibrated scales. The difference between 1 division of
main scale and 1 division on vernier scale is known as the least count.
Principle of working of vernier depth gauge is also the same as that of vernier caliper
while the principle of the depth micrometer is same as that of a micrometer. They,
however, differ in construction as can be seen in figures. Both have beam which rests on
the top of the hollow to be measured.
11
Laboratory-IV
Figure 3.1 : Vernier Height Gauge
Figure 3.2 : Vernier Depth Gauge
3.4 PROCEDURE
(a)
Study the main elements of depth gauge, base, thimble, lock nut and depth
gauge attachments.
(b)
Study the main elements of height gauge, main scale, vernier scale, base,
movable arm, scriber, adjusting scales.
(c)
Calculate the least count and maximum range of measurement.
(d)
Read off any three positions of the main and subsidiary scale and record the
readings.
(e)
Measure the given piece and record as per the standard proforma.
3.5 PRECAUTIONS AND CARE OF INSTRUMENT
Height Gauge
12
(a)
Do not allow the instrument to come in contact with dust and dirt. It is better
kept in its case.
(b)
Temperature rise of height gauge by room heating or by hands should be
avoided while measuring and checking longer lengths. Even keeping contact
with fingers for a longer time may affect the reading, especially if depth
gauge attachment is long.
(c)
The sliding head (with vernier mounted on its auxiliary head) and fine
adjustment should be checked for squareness with beam and parallism of
surface. There should be no nicks, scratches, corrosion or any other damage.
(d)
Check for rocking of base on surface plate at various points.
(e)
Check the height gauge measuring and marking arm for zero error. The zero
of vernier and main scale should coincide when measuring and marking arm
rests on surface plate.
Measurement and
Metrology Lab
Depth Gauge
(a)
Make sure the reference surface, on which depth gauge is rested is true flat
and square.
(b)
Make sure the gauge itself is true and square.
(c)
The gauge while measuring should neither be tipped forward nor backward.
In case of tilted instrument, measuring end will not touch squarely on the
surface to be measured and erroneous readings will be observed.
(d)
Too much pressure should not be applied on the beam or measuring bar as it
will have lifting tendency on the slide and result in readings different from
actual ones.
(e)
In using a depth gauge, press the slide firmly on reference surface by hand
pressure on it. Manipulate the gauge beam to measure depth. Be sure to
apply only standard light measuring pressures of 1/4 kg to 1/2 kg (like
marking a light dot on paper with a pencil) on the beam.
(f)
The results are greatly affected by the “feel” of the contact between the tool
and the work. Some practice is required before confidence is developed.
When using long extensions, the heat of hands can be transmitted to
extensions easily and thus result in incorrect reading. Hence longer
extensions should be handled cautiously.
13
Laboratory-IV
EXPERIMENT NO. 4 : MEASUREMENT WITH DIAL
INDICATOR USING SURFACE
PLATE AND ACCESSORIES
Structure
4.1
Introduction
Objectives
4.2
Instruments Used
4.3
Working Principle
4.4
Procedure
4.5
Precautions
4.6
Sources of Error
4.7
Limitations
4.1 INTRODUCTION
Dial indicators are instruments used for making and checking linear measurements.
These instruments are used for centering the work on machines for checking the
eccentricity and for visual inspection of work.
Objectives
After performing this experiment, you should be able to
•
acquire skill of measuring with dial indicator.
•
know the range and the least count.
•
use the indicator in various shop situations with different types of holders.
4.2 INSTRUMENTS USED
(a)
Dial indicator – range 0 to 10 mm, LC = 0.01 mm, with stand.
(b)
Surface plate, 450 × 450 mm
(c)
V-block and C-clamp.
4.3 WORKING PRINCIPLE
The linear movement of plunger is converted into rotary movement of needles on a dial.
This is achieved by means of a rack and pinion, and a gear train arrangement.
Figure 4.1
14
Measurement and
Metrology Lab
4.4 PROCEDURE
For Checking Flatness
(a)
First check the accuracy of the dial indicator with some standard pieces from
the box of slip gauges and record the deviations in a table. The dial gauge is
fitted on the stand with dial in vertical plane. The stem of the dial gauge is
also vertical. The end of the stem can be brought in contact with the job on
flat surface. The stand of the dial gauge can move freely on the surface plate
so the stem can be brought in contact of the surface to be checked. If
deviation in dial gauge reading is not significant, then the surface is smooth
and flat.
(b)
Place the flat piece on the surface plate.
(c)
Mount the dial indicator on the stand and take at least four readings on the
job at different positions.
(d)
Record the readings in the table and note the deviations from flatness (if
any).
For Checking Concentricity of a Round Shaft
(a)
Place the round job on the V-block.
(b)
Mount the dial indicator on the stand and take different readings on the job
by rotating it.
(c)
Record the readings in the table of observations and note the deviations (if
any) for checking the circularity.
(d)
Note the maximum eccentricity.
Circle
Dial
Indicator
Part
Part
(a)
(b)
(c)
Figure 4.2 : Using Dial Indicator on Round Bar
4.5 PRECAUTIONS
(a)
Some initial loading must be given at any given readings.
(b)
The plunger should not be allowed to strike the work with force otherwise
the teeth of the gears and rack will be damaged.
(c)
The accuracy of the dial indicator may be checked with the help of slip
gauges periodically.
15
Laboratory-IV
4.6 SOURCES OF ERROR
(a)
Some variations may be there in the indicator when readings are being
taken. This may be avoided if the pointer movement is damped properly.
(b)
The operating pressure required on the measuring head to obtain zero
reading may cause some error if it is not kept constant over the whole range.
(c)
The plunger should move only within specified limits, otherwise error will
crop in.
4.7 LIMITATIONS
The instrument may not be usable for a larger range. The main limitation of the
instrument is its comparatively small range of measurement. The minimum reading of
0.01 mm also has its limitation.
16
EXPERIMENT NO. 5 : MEASUREMENT WITH
COMBINATION SET
Measurement and
Metrology Lab
Structure
5.1
Introduction
Objectives
5.2
Instruments Used
5.3
Working Principle
5.4
Procedure
5.5
Precautions and Care of Instruments
5.6
Sources of Error
5.1 INTRODUCTION
This is the most adaptable and commonly used non-precision instrument to be used in
layout and inspection work. Combination set is used as a rule, a square, a depth gauge, a
height gauge and a level.
Objectives
After performing this experiment, you should be able to
•
understand the uses of combination set,
•
measure angles by using combination set, and
•
check the sequences by using combination set.
5.2 INSTURMENTS USED
Combination set 450 mm with scale of 450 mm, square head, centre head, protractor
head, levels and scribes.
5.3 WORKING PRINCIPLE
The combination set is a non-precision instrument. Because of geometry involved the
angles are usually more difficult to measure then linear dimension. This is most
commonly used in layout and rough inspection work. The combination set consists of
scale, square head, protractor head and centre head. Its usefulness lies in incorporation of
such essential features as try square, mitre-square, protractor and centre-square. The
protractor like any common protractor measures angle but has additional facility of being
movable. It consists of a heavy scale, which is grooved in the center along its entire
length. It is in this groove that square head, centre head or protractor head is fixed. The
protractor head may be used in conjunction with the rule as a protractor for checking
angles or scribing lines at angles to reference plane. The square head is used in
conjunction with the rule as a try square. The square head is used for checking
squareness and for marking purposes. It can also be used for measuring depth up to the
accuracy of 0.5 mm. The centre head is used for finding the centre of bar stocks. The
features of combination set are shown in Figure 5.1.
17
Laboratory-IV
Figure 5.1 : Combination Set
5.4 PROCEDURE
For Measuring Angles
(a)
Fix the protractor head on the scale.
(b)
Place the scale on one side of the angle to be measured.
(c)
Adjust the protractor by rotation, so that its working surface should touch
the adjacent side of the angle to be measured.
(d)
Lock the protractor.
(e)
Read the angle on the scale.
For Checking Squareness
(a)
Fix the square head on the scale.
(b)
Check the spirit level for parallelism.
(c)
Check the surfaces for squareness by placing the job on the surface plate.
For Marking Centre
(a)
Fix the centre head on the scale.
(b)
Hold the bar stock beneath the scale.
(c)
See that the sides of centre head are touching the bar stock.
(d)
Scribe a line along the scale in each position and rotate the bar stock for
three positions.
(e)
The centre of the triangle formed will be the centre of the job.
5.5 PRECAUTIONS AND CARE OF INSTRUMENTS
(a)
The job should be held in the left hand and the instrument in the right hand.
(b)
The surfaces to be checked should be clean.
(c)
The edge of the scale should be straight.
(d)
Spirit level should be checked before taking reading.
(e)
See that there are no nicks and scratches on the base of heads.
(f)
While checking for squareness and measuring angles, stand facing the
surface and light and check the light passing through the scale or base of
measuring instrument.
5.6 SOURCES OF ERROR
18
(a)
The edge of scale may not be straight.
(b)
Zero error in the protractor scale may exist.
(c)
Working surfaces of different heads may be worn.
EXPERIMENT NO. 6 : MEASUREMENT OF ANGLES
WITH BEVEL PROTRACTOR
Measurement and
Metrology Lab
Structure
6.1
Introduction
Objectives
6.2
Instruments Used
6.3
Working Principle
6.4
Procedure
6.5
Precautions and Care of Instruments
6.6
Sources of Error
6.1 INTRODUCTION
It is the simplest instrument for measuring angles between two faces. It consists of two
arms and an engraved circular scale. The two arms can be set along the faces between
which the angles to be measured. The level protractor can measure angles to five minutes
of a degree. In this experiment, you will be introduced to the measurement of angles with
bevel protractor.
Objectives
After performing this experiment, you should be able to
•
acquire the skill of measuring angles with the bevel protractor, and
•
know the range of measurement and to calculate the least count of the bevel
protractor.
6.2 INSTRUMENTS USED
Vernier bevel protractor (0 to 360o)
Least count = 5′.
Surface plate 450 × 450 mm.
Holding device to suit particular job.
6.3 WORKING PRINCIPLE
It consists of a base plate attached to the main body and an adjustable blade attached to a
circular plate containing vernier scale. Adjustable blade is capable of rotating freely
about the centre of main scale engraved on the body of the instrument and can be locked
in any position by using clamping nut.
An attachment is provided at the top for the purpose of measuring acute angles.
Least Count
Fixed scale is divided into degrees and the vernier is graduated such that
12 of its divisions are equal to 23 divisions on the main or fixed scale. The
divisions on the fixed scale are in degrees. The difference between one division of
vernier space and two of the fixed scale is 1/12 degree. Therefore, the minimum
reading of the instrument is 1/12o or 5′.
19
Turret
Laboratory-IV
Slow Motion Device
Body
Blade Locking
Nut
Scale
Blade
Stock
Working Edge
Figure 6.1 : Bevel Protractor
80
70
60 50 40 30
20
80
90
10
0
0
10
0 40 50 6
07
20 3
0
0 40 50 60
20 3
70
10
80
90
80
70
Figure 6.2 : Universal Bevel Protractor
Figure 6.3 : Vernier Protractor Reading 20o 15′
6.4 PROCEDURE
20
(a)
Study the bevel protractor and identify its main parts.
(b)
Introduce the adjustable blade in the slot of body and clamp it with the help
of knob in the convenient position.
(c)
Place the working edge of the stock on one surface of the job and rotate the
turret holding the blade so that the working edge of the blade coincides with
another surface of the job. Fix the turret and read the angle.
(d)
Measure the angles of the sample pieces with the bevel protractor and record
the reading in the proforma suggested.
Measurement and
Metrology Lab
6.5 PRECAUTIONS AND CARE OF INSTRUMENT
(a)
Use the instrument with care.
(b)
While readings are taken your eyes must be in front of the matching lines.
(c)
Always check the tightness of clamping screws before taking reading.
6.6 SOURCES OF ERROR
(a)
Base plate and adjustable settings.
(b)
Blade and stock should be made parallel to the surfaces of the sample job
otherwise the angles measured will be wrong.
(c)
Instrument has marking errors.
(d)
Parallax errors may occur.
21
Laboratory-IV
EXPERIMENT NO. 7 : STUDY AND USE OF SLIP
GAUGES
Structure
7.1
Introduction
Objectives
7.2
Instruments Used
7.3
Description
7.4
Precautions and Care of Instruments
7.5
Sources of Error
7.1 INTRODUCTION
Slip gauges are measuring bodies of hardened steel. These gauges are of rectangular
form, and are made of a high steel, hardened throughout and stabilised by means of a
suitable heat treatment. It is economical to have slip-gauges made individually to all sizes
of standard that are likely to be required, and they are normally slipped in carefully
selected sets, the size of any required standard being made up by combining suitable slip
gauges.
Objectives
After performing this experiment, you should be able to
•
acquire skill in wringing of gauge blocks,
•
acquire skill in selecting minimum number of gauges to make up
measurements,
•
understand about the care and maintenance of slip gauges, and
•
know about the use of slip gauges in conjunction with surface plate.
7.2 INSTRUMENTS USED
(a)
Gauge block set (103 pcs)
(b)
Surface plate, 450 × 450 mm
(c)
Magnetic base holder
(d)
Steel foot rule.
A number of blades (also called “slips”) of different thicknesses are assembled together
in a convenient holder. It is not necessary to have slips of all thicknesses in a single
holder. The common practice is to have a number of slips (blades) which can be arranged
in combinations to give all the desired sizes. For instance to obtain a thicknesses of 0.125
mm slips of thickness 0.075 mm and 0.05 mm respectively can be combined. It should be
ensured that surfaces maintain perfect contact in combination and for the reason only
minimum number of slips should be used. The combining is known as wringing of
gauges and is partly due to molecular attraction (adhesion) and partly due to pressure.
The gauges will not wring if there is any dirt between them.
7.3 DESCRIPTION
Slip gauges are measuring bodies of hardened steel. For measuring and testing they can
be built up to various dimensions. This is accomplished by pressing together the working
faces of two gauge blocks or by wringing the gauges. These are used as standards of
22
measurement. For wringing, the slips are first placed at right angle and then rotated
through 90o under pressure of about 5 N/mm2.
Measurement and
Metrology Lab
Slip gauges are classified according to their accuracy :
(a)
‘C’ Grade : This generally used in workshop for checking dimensions of
the products.
(b)
‘B’ Grade : This grade is used in factories for checking the size of the
articles.
(c)
‘A’ Grade : This is used for reference purpose.
(d)
‘AA’ Grade : This is termed as master slip gauge and is not generally in
use.
Slip gauges are available in inch units and metric units as a set consisting of number of
pieces.
Application of Slip Gauges
•
Calibration and checking of precision measuring instruments.
•
Pre-setting of machine tools.
•
Pre-setting of fixtures and tools.
•
Building up accurate dimension.
The five most commonly used sets contain 81, 49, 41, 35 and 25 pieces respectively. And
in Metric units sets of 103, 76, 56, 48 and 31 pieces are available.
The building up size combination for length of 2.265 mm and 38.015 mm with a set of
103 pcs is given in the “Reading Taken” sequence. As a guide for building up
dimensions the range of some metric sets are given below :
Metric Set
Set of 103 Pieces
Range
Steps
Pieces
1.01 – 1.49
0.01 mm
49
0.50 – 24.5
0.5 mm
49
25 – 100
25 mm
4
1.005
−
1
Total : M 103
Set of 87 Pieces (Special Set)
Range
Steps
Pieces
1.001 – 1.009
0.001 mm
9
1.01 – 1.49
0.01 mm
49
0.5 – 9.5
0.5 mm
19
10 – 90
10 mm
9
1.005
−
1
Total : M 87
Other sets in this group are 76, 56, 48 and 31 pieces.
Slip Gauge Accessories
The field of application is considerably advanced by a few simple accessories viz.,
holders, jaws, scribers and centre point etc. (See Figure 7.1).
23
5
1.005
6
25
Laboratory-IV
Figure 7.1 : Gauge Blocks
Figure 7.2 : A Set of Slip Gauges
Reading Taken
Building up size combination (sets of 103 pcs)
(a)
2.265 mm
(b)
38.015 mm
1st slip 1.005 mm
1st slip gauge 1.005 mm
2nd slip 1.260 mm
2nd slip gauge 1.010 mm
Length 2.265 mm
3rd slip gauge 11.000 mm
4th slip gauge 25.000 mm
Length = 38.015 mm
7.4 PRECAUTIONS AND CARE OF INSTRUMENTS
24
(a)
The surface of the gauge must be protected against rust with neutral
petroleum jelly or some other anticorrosive preparation.
(b)
The gauges should be protected from dust and dirt.
(c)
The gauges should be used under controlled conditions of temperature and
maintained at constant temperature.
(d)
Wipe the gauge clean with chamois leather everytime before use.
(e)
The excessive pressure during wringing of gauges may cause damage to the
surface.
(f)
When building up size combination, see that you start with the minimum
value of the right hand side of the decimal.
(g)
Never drop a slip gauge.
(h)
Never strike slip gauges with other metallic objects.
(i)
Use minimum number of gauges for building up size combination.
7.5 SOURCES OF ERROR
(a)
Improper wringing of the gauges.
(b)
Noting the dimensions incorrectly from the gauge.
(c)
The error may occur due to room not being maintained at proper
temperature.
Measurement and
Metrology Lab
25
Laboratory-IV
EXPERIMENT NO. 8 : MEASUREMENT OF THREAD
CHARACTERISTICS
Structure
8.1
Introduction
Objectives
8.2
Material Required
8.3
Instruments Used and Specifications
8.4
Theory
8.5
Precautions
8.1 INTRODUCTION
Thread can be defined as a raised, helical rib or ridge around the exterior of a cylindrical
shaped object or the interior of a hole. Threads are found on screws, nuts and bolts. In
this experiment, you will be introduced to the measurement of thread characteristics.
Objectives
After performing this experiment, you should be able to
•
know and identify various kinds of threads,
•
explain the important thread characteristics,
•
acquire the skill of comparing the threads and finding the pitch, and
•
acquire the skill of measuring effective thread diameter.
8.2 MATERIAL REQUIRED
A standard size wooden box with about one dozen prepared samples, suitable for
measurement, contains assortment of whitworth as well as metric threads.
Maximum nominal diameter = 20 mm
5 metric threads, 5 whitworth threads.
8.3 INSTRUMENTS USED AND SPECIFICATIONS
(a)
Screw pitch gauge (Metric and whitworth).
(b)
Screw thread micrometer (Metric and whitworth).
8.4 THEORY
A few types of threads are (Figure 8.1) :
(a)
Vee,
(b)
Square,
(c)
Buttress,
(d)
Acme, and
(e)
Knuckle.
Common definitions involved in thread characteristics are shown in Figure 8.1 which
show outline of a typical V-type screw thread and other threads.
26
Different characteristics of threads are :
Measurement and
Metrology Lab
(a)
Full diameter (major) or diameter at top of the thread.
(b)
Core diameter (minor) or diameter at bottom of thread.
(c)
Effective Diameter (Pitch Diameter) : The length of a line perpendicular
to, and intersecting the axis, between the points where it meets the sloping
flanks of the threads on opposite sides.
(d)
Pitch : The distance measured parallel to the axis of the screw, between
corresponding point on consecutive thread contours.
(e)
Thread Angle : The angle between thread flanks measured in an axial plane
section.
(f)
Radius of crest.
(g)
Radius of root.
Pitch, thread angle and effective diameter are some of important parameters to be
measured.
(a)
Full Diameter : With ordinary micrometer with anvils sufficient to span
two threads, check first a standard cylinder and then the screw diameter.
(b)
Core Diameter : An ordinary micrometer with a pair of special V-pieces
check the diameter over the roots of threads.
(c)
Effective Diameter.
Three Wire Method
Checking the effective diameter when a screw is measured over wires
is given below for a general case. Distance over wires:
De = W +
where
p
L ⎛
L⎞
cot − ⎜1 + cosec ⎟ d
2
2 ⎝
2⎠
De = effective diameter,
d = diameter of wire,
p = pitch,
L = angle of thread,
W = outer diameter of thread with wires, and
D = nominal diameter or major diameter.
L
D
W
De
Figure 8.1
Whitworth Threads
Depth of thread = 0.64 p, L = 55o
De = W – 13.16568 d + 0.96049 p
or
D = W + 3.1675 d + 1.6005 p
American Metric Thread
Depth of thread = 0.6495 p, L = 60o
De = W – 3 d + 0.86603 p
or
D = W – 3 d + 1.5155 p
[Note : Limiting wire size for thread measurement.]
Thread Form
Max. Wire Dia
Min Wire Dia
27
Laboratory-IV
(d)
Whitworth
0.853 p.
0.506 p.
Metric
1.01 p.
0.505 p.
Pitch : The lead or pitch of a single thread screw is the distance measured
with the help of vernier caliper and dividing this distance by number of
threads in between.
Threads can also be checked by screw gauge set (Figures 8.2(a), (b), (c), (d)
and (e)).
PITCH
1/6 D
55
D
0
1/6 D
(a)
½P
P
(b)
P
45
0
(c)
0.37P
½ P+0.01
P
29
0
(d)
P
RAD ¼ P
P
1/2
(e)
Figure 8.2
(e)
28
Thread Angle : Measured by (a) Screw pitch gauge approximately and
(b) Toolroom microscope accurately.
A glass template is fixed in the microscope. On this template, thread profiles
are etched with high accuracy. The individual profile outlines are
successively brought into the field of view. Thereby, it will be attempted to
bring the outline in question into coincidence with the thread profile of the
work piece and the details of thread characteristics read from the template.
Measurement and
Metrology Lab
8.5 PRECAUTIONS
(a)
When making a test, micrometer must be located at right angles to the axis
of the screw being measured.
(b)
Threads must be fixed on the table of the microscope, so that observation is
not disturbed.
(c)
Proper lighting of the object will assist in accurate recording of
measurements.
(d)
Screw pitch gauge with a stopper must be used especially in case of small
nuts.
29
Laboratory-IV
EXPERIMENT NO. 9 : MARKING AND MEASURING
EXERCISE WITH ALL
MEASURING DEVICES
Structure
9.1
Introduction
Objectives
9.2
Materials Required
9.3
Instruments Used
9.4
Working Principle
9.5
Procedure
9.6
Precautions and Care of Instruments
9.7
Sources of Error
9.1 INTRODUCTION
In this experiment, you will be introduced to the marking and measuring exercise with all
measuring devices.
Objectives
After performing this experiment, you should be able to
•
develop skill of reading the drawings from given views, and
•
develop skill of transferring the dimensions from the drawing on to the job,
using marking devices and measuring instruments.
9.2 MATERIALS REQUIRED
(a)
MS/Cl block or plate with three surfaces machined accurately and
perpendicular to each other.
(b)
Pieces of chalk or Prussian blue paste.
9.3 INSTRUMENTS USED
30
(a)
Marking table
(b)
Height gauge with carbide tipped scriber
(c)
Ordinary scriber with magnetic base stand
(d)
Slip gauge set
(e)
Angle plate
(f)
Divider
(g)
Scale
(h)
Set of punches
(i)
Dial indicator
(j)
Set of parallel blocks.
9.4 WORKING PRINCIPLE
Measurement and
Metrology Lab
Marking is based on the principle of transferring the dimensions from the measuring
instruments to the job by means of scriber.
9.5 PROCEDURE
(a)
Clean the marking table and marking instruments.
(b)
Check mutual perpendicularity of the three machined surfaces of workpiece
with angle plate.
(c)
Apply chalk or blue paste on the surfaces to be marked.
(d)
Place the workpiece in xy-plane on marking table.
(e)
Set the scriber for different dimensions parallel to xy-plane with the help of
height gauge, slip gauge and scribe the respective line on the marking
surface.
(f)
Scribe all the lines inclined with the marking table with the help of scale and
scriber.
(g)
Make punch marks on the scribed lines.
(h)
Repeat marking steps of other reference planes, i.e. yz and xz.
9.6 PRECAUTIONS AND CARE OF INSTRUMENTS
(a)
Scriber should be fixed firmly in the height gauge.
(b)
Reference planes should not have any burrs and should be mutually
perpendicular to each other.
(c)
Marking table should be leveled.
(d)
Scriber point should be sharp and scriber should be perpendicular to the
marking surface.
(e)
Movement of scriber on marking table should be smooth.
(f)
All the dimensions should be marked carefully.
(g)
All the dimensions should be verified before punch marking the scribed
lines.
9.7 SOURCES OF ERROR
(a)
Damaged base of height gauge.
(b)
Loose holding of scriber in the height gauge.
(c)
Tilting of height gauge during marking.
(d)
Bluntness of scriber.
(e)
Scribing wrong dimensions from wrong reference plane.
31
Laboratory-IV
EXPERIMENT NO. 10 :STUDY OF INSPECTION
GAUGES SUCH AS PLUG,
SNAP, AND THREAD
GAUGES
Structure
10.1 Introduction
10.2 Go and No Go Gauging
10.1 INTRODUCTION
Gauges are inspection tools of rigid design without a scale, which serve to check the
dimension of manufacturing parts. Production gauges are of various types, but the
majority is in the form of limit gauge. These are designed to cover a very wide range of
work. The general form of limit gauge is of the fixed type. That is to say, the gauging
contact elements remain fixed, during the gauging process. Gauging elements may,
however, be provided with the means of size adjustment. Limit gauging is not confined
to the use of simple gauges such as those normally designed to check the size of the
shafts and holes. The progressive need for checking fine tolerances has led to the
introduction of that form of limit gauging in which an instrument, e.g. a comparator,
fitted with an indicator working between specified positions, is used without reference to
the actual sizes of the features being examined.
Objectives
After performing this experiment, you should be able to
•
understand the fundamental of the gauges and their classifications, and
•
explain the working principles of various types of gauges and their
application.
10.2 GO AND NO GO GAUGING
Plug Gauges
These gauges are “GO” and “NO GO” type, and used for gauging holes. This
gauge is made from hardened steel cylinder, very accurately ground to the lower
limit diameter of hole. If hole is near lower limit the gauge enters the hole
smoothly under light push. This gauge is stamped “GO”. If hole diameter is close
to upper limit it is stamped “NO GO”. A NO GO gauge is finished as GO gauge to
be used in the hole and if it enters the hole, the hole is unacceptable. Hence NO
GO should not pass through the hole. The GO gauge is longer in length because it
is likely to wear as it rubs with inside of hole. The NO GO is made short in length
since it does not pass through the hole hence no wear.
No Go Gauge for Hole
32
Figure 10.1 : Go and
Figure 10.2 : Standard Ring and Plug Gauges
Measurement and
Metrology Lab
Figure 10.3 : Progressive and Double Ended Limit Plug Gauge
In the renewable end plug gauge, the ‘GO’ end is renewable as it is subjected to
wear. In order to increase considerably the wearing properties of plug gauges they
are chrome plated. A further advantage of chromium plating is that when, finally,
the surface wears it can readily be renewed by plating and brought to the original
dimensions by grinding and lapping.
Pilot Gauge
The possibility of an operator to insert a plug gauge obliquely into the hole that is
to be checked so that it jams across the hypotenuse of the triangle shown by the
dotted line is avoided altogether in the ‘Pilot’ gauge by machining a groove behind
the front of the gauge as in Figure 10.4.
Figure 10.4
Figure 10.5 : Taper Plug and Ring Gauge
It will be seen that there is first a small chamfer, then a narrow ring or pilot, the
same diameter as the body of the gauge, after this the groove and finally the main
body of the gauge.
If the gauge is fitted, the pilot or leading portion is of the nature of an ellipse in
respect to the hole so that on entering the hole it touches at two points across the
major axis, which is the diameter of the plug. If the pilot can enter the hole, it is
sufficiently large assuming the hole to be round-for the rest of the gauge to enter.
Thus a ‘Pilot’ will enter a ‘size for size’ hole without jamming.
Snap Gauges
For checking external diameters a ring gauge having two limiting diameters could
be employed in a similar manner, but this type had very largely been superseded
by the snap gauge (Figure 10.6).
This gauge is of flat shape and provided with two jaws of caliper form. One jaw is
usually marked ‘GO’ and corresponds to the maximum allowable diameter or plus
dimension, the other jaw is marked ‘NO GO’ and show the minimum allowable or
minus dimension. This form of gauge and all other two unit gauges are often
termed GO and NO GO or G and NG gauges.
33
Laboratory-IV
(a) Double Snap Gauge, the “No Go”
Check is Made by the Inner Faces
(b) Adjustable Gauge
Figure 10.6 : Snap Gauge
A further improvement is to substitute two pairs of contact for the parallel faces of
jaws as indicated. In this way, by making one of each pair of stops adjustable it is
possible to set the gauge to any two limiting dimensions and also later on, to take
up any wear effects on the contacts.
Thread Gauges
During mass production of threaded parts, it is uneconomical to measure each
individual element, since measuring can eventually be more expensive than the
workpiece. Instead, screw thread gauges, which permit a simultaneous testing of
all thread dimensions, will be used.
The external thread is tested with standard ring thread gauge and the inside thread
with the standard plug thread gauge as shown in Figure 10.7. The gauges must fit
in such a way that they can be screwed in or out without any clearance in between.
The smooth cylinder plug gauge is used for testing the core diameter of the internal
thread. The testing depends on the sensitiveness. Moreover a thread, which can be
screwed in with a snug fit, does not yet offer the guarantee that it fits properly. The
flank diameter and the bearing of the flanks cannot be tested accurately with
standard thread gauge, therefore these are seldom used.
l
GO
l
NO GO
Figure 10.7 : Thread Gauge
Thread limit gauges are used for fast and accurate testing of all thread dimension.
The same as with all other limit gauges, they have a ‘GO’ and ‘NO GO’ side.
Internal thread is tested with limit screw plug.
Taper Gauges
If tapers and taper holes fit together, they must have the same conicity. Testing the
serviceability of a taper consists mainly in the determination of proper conicity. It
is well known that the dimensions determine conicity of a taper: big diameter D,
small diameter d and length l. The measuring of these sizes is not a simple matter
and it is generally tested at the same time with special taper gauges, which contain
the prescribed dimensions. Standardized tapers (Morse tapers, Metric tapers) are
tested with standard taper gauges. Thus, not only the individual dimensions are
ascertained, but they are also determined. If the taper ring gauge corresponds with
the taper or the taper hole with the taper plug gauge as shown in Figure 10.8, the
diameters of the taper are correct.
34
GO
NO GO
Measurement and
Metrology Lab
Figure 10.8 : Limit Taper Plug Gauge
When the taper diameters vary within certain limits, two tolerance marks
corresponding to the tolerance are engraved on the taper gauge. Before testing the
taper surfaces of the workpiece, the testing instrument must be cleaned thoroughly.
An equal contact of the tapers will be ascertained by means of the frictional
contact method. The surface of the taper (taper plug or workpiece) will, in
direction of the longitudinal axis, be provided with two pencil lines, which are
staggered by 90o. After fitting workpiece and gauge together they are twisted
somehow against each other with slight pressure. The lines must be evenly blurred
out. If this is not the case, the taper has uneven contact and the two tapers are not
identical.
35
Laboratory-IV
EXPERIMENT NO. 11 : MEASUREMENT OF TAPERS
(EXTERNAL AND
INTERNAL)
Structure
11.1 Introduction
Objectives
11.2 Instruments Used
11.3 Working Principle
11.4 Procedure
11.5 Precautions
11.6 Sources of Error
11.1 INTRODUCTION
In this experiment, you will be introduced to the measurement of tapers – external and
internal.
Objectives
After performing this experiment, you should be able to
•
calculate the taper angle both external and internal, and
•
understand the function of rollers for calculating the taper angle.
11.2 INSTRUMENTS USED
(a)
Micrometer,
(b)
Depth gauge/height gauge,
(c)
Surface plate,
(d)
Balls of known dimension 2 of each size,
(e)
Rollers of known dimension 2 of each size,
(f)
Gauge block set.
Least Count/minimum reading of
(a)
Micrometer = 0.01 mm
(b)
Micrometer depth gauge = 0.01 mm
(c)
Vernier height gauge = 0.02 mm.
11.3 WORKING PRINCIPLE
These methods make use of trigonometric functions.
The required dimensions are computed by taking several readings with instruments.
36
Measurement and
Metrology Lab
D
θ
d
Figure 11.1 : Taper Angle
11.4 PROCEDURE
Theory
Taper angles of turned parts of standard taper plug can be checked by measuring
the diameters at two sections and the distance between these sections. Referring to
the Figure 11.1, if D and d are diameters at the section BB and AA respectively and
H is the distance between these diameters, then from the triangle ABC it follows
that
Tan θ =
D−d
2H
This method is applied for measuring the taper angle of a component such as a
taper plug gauge.
For External Taper
(a)
Stand the taper plug gauge (job) with its small end on the surface plate.
(b)
Select two piles of slip gauges (S1).
(c)
Place the roller of diameter (d) on the top of the block of slip gauges (S1).
(d)
Standardize the micrometer carefully on a slip gauge with a roller on each
side.
(e)
Measure the size of the job or gauge over the rollers.
(f)
Select another value of slips (S2) and place the roller over it.
(g)
Measure the size over the rollers M2 by micrometer.
For Internal Taper
(a)
Hold the ring gauge or job almost horizontal.
(b)
Roll the smaller ball gently inside the gauge or job until it rests.
(c)
Stand the gauge or job, small end down, on the surface plate.
(d)
If the ball protrudes, place the gauge on two equal piles of slips sufficient to
keep the bottom of the ball clear of the surface plate.
(e)
Lower the depth attachment with the height gauge until it just touches the
top of the ball.
(f)
The height gauge reading is noted and the procedure repeated about three
times to get average value.
(g)
Next remove the smaller ball and insert the larger one.
(h)
Note the height with the larger ball.
(i)
Note the height of the top surface of the gauge (job).
37
Laboratory-IV
11.5 PRECAUTIONS
(a)
The taper gauge (or job) should be set up on its small end.
(b)
The roller should be of same diameter as small end.
(c)
Rollers must not swing under measuring pressure.
(d)
Check the zero error of the measuring instruments.
(e)
Check that the balls used for internal taper have true spherical surface.
11.6 SOURCES OF ERROR
38
(a)
Misalignment of rollers.
(b)
Uneven pressure while taking reading over the rollers.
(c)
Error due to improper wringing of slip gauges.
(d)
The height gauge may not be in contact with the highest point of the ball.
EXPERIMENT NO. 12 :MEASUREMENT OF SPUR
GEAR CHARACTERISTICS
Measurement and
Metrology Lab
Structure
12.1 Introduction
Objectives
12.2 Instruments Used
12.3 Working Principle
12.4 Procedure
12.5 Observations and Calculations
12.6 Precautions and Care of Instruments
12.7 Sources of Error
12.1 INTRODUCTION
Spur gears are straight-toothed gears with radial teeth that transmit power and motion
between parallel axes. They are widely used for speed reduction or increases, torque
multiplication, resolution, and accuracy enhancement for positioning systems. In this
experiment, you will be introduced to the measurement of spur gear characteristics.
Objectives
After performing this experiment, you should be able to
•
know and identify the principle characteristics of a spur gear, and
•
acquire the skill of measuring characteristics of a gear with gear tooth
vernier.
12.2 INSTRUMENTS USED
(a)
Gear tooth vernier
(b)
Vernier caliper 12″ or 300 mm
(c)
Bench vice.
Least count of
(a)
Gear tooth vernier, 0.02 mm
(b)
Vernier Caliper, 0.02 mm
(c)
Bench vice
Figures 12.1 : Gear Tooth Nomenclature
39
Laboratory-IV
(a)
Diagram of gear tooth vernier (Figure 12.1).
(b)
Spur gear tooth profile for different nomenclature (Figure 12.2).
Figure 12.2 : Approximate Representation of Involute Spur Gear Teeth
Three sample spur gears in metric units for measurements of different
characteristics may be used.
12.3 WORKING PRINCIPLE
Brief description of measuring of tooth thickness by gear tooth vernier is given. It
consists of a horizontal and a vertical vernier slide. It is based on the principle of vernier
scale. An independent tongue which is adjusted independently by adjusting the slide
screws on graduated beams measures the thickness of a tooth at pitch line and the
addendum.
Terminology of Gear Tooth
(a)
Pitch Circle Diameter (PCD) : It is the diameter of a circle, which by pure
rolling action would produce the same motion as produced by the toothed
gear wheel.
D = pitch circle diameter
OD = outside diameter or addendum circle diameter
T = number of teeth
(c)
Module : It is defined as the length of the pitch circle diameter per tooth.
Module, m = D/T and is expressed in mm.
(d)
Circular Pitch (CP) : It is the arc distance measured around the pitch circle
from the flank of one tooth to a similar flank in the next tooth.
CP =
40
πD
= πm
T
(e)
Addendum : This is the radial distance from the pitch circle to the top of
the tooth. It is equal to one module in standard depth of tooth.
(f)
Clearance : This is the radial distance from the tip of a tooth to the bottom
of the mating tooth space when the teeth are symmetrically engaged. Its
standard value is 0.157 m or 0.25 m.
(g)
Dedendum : This is the radial distance from the pitch circle to the bottom of
tooth space.
Dedendum = Addendum + Clearance
Measurement and
Metrology Lab
= m + 0.157 m = 1.157 m.
or
(h)
1.25 m (metric gearing system)
Tooth Thickness : This is the arc distance measured along the pitch circle
from the intercept with one flank to the intercepts with the other flank of the
same tooth.
For a correct gear t′ = D sin (90/T),
D = PCD (chordal), T = No. of teeth
Also chordal depth c = (D/2) (1 – cos (90/T))
12.4 PROCEDURE
For Finding PCD, Module, Addendum, Dedendum and Clearance
(a)
First find the blank diameter OD by a vernier caliper and also count the
number of teeth T of the spur gear.
(b)
Next calculate pitch circle diameter D =
(c)
Find addendum, clearance, pitch, module and dedendum as per formulae
given in the theory.
OD
.
2⎞
⎛
⎜1 + T ⎟
⎝
⎠
For Chordal Tooth Thickness (Using Gear Tooth Caliper) (Figure 12.3)
(a)
Set the chordal depth (addendum) on the vertical side of gear tooth vernier
and then insert the jaws of the instrument on the tooth to be measured.
(b)
Adjust the horizontal vernier slide by the fine adjusting screw so that the
jaws just touch the tooth.
(c)
Read the horizontal vernier slide and note the reading. It gives the chordal
thickness of tooth.
(d)
Repeat the observations for different teeth.
(e)
Compare the values of different characteristics with the standard value and
set the percentage error.
Figure 12.3 : Measuring Gear-tooth Thickness and Profile with (a) A Gear-tooth Caliper and
(b) Pins for Balls and a Micrometer
(Source : American Gear Manufacturers Association)
41
Laboratory-IV
12.5 OBSERVATIONS AND CALCULATIONS
Zero error horizontal vernier slide =
Zero error of vertical vernier slide =
No. of teeth on the spur gear
Pitch circle diameter D =
Module m = D/T mm
Addendum = One module = m
Dedendum = Addendum + Clearance
= m + 0.157 m
= 1.157 m (1.25 m)
Clearance = 0.157 m (m is module of teeth)
Circular Pitch P = π m
Tooth thickness of gear tooth = t
Standard value of tooth thickness
(Chordal) t′ = D sin (90/T)
% age error =
12.6 PRECAUTIONS AND CARE OF INSTRUMENTS
(a)
Gear surface should be cleaned properly before setting the instruments.
(b)
Zero error of the instruments should be taken into account.
(c)
Repeat the experiment by setting the instrument on different teeth.
12.7 SOURCES OF ERROR
42
(a)
The adjusting of jaws of gear tooth caliper may not be proper.
(b)
Zero error may be there.
(c)
Jaws may be worn out.
EXPERIMENT NO. 13 :MEASUREMENT OF BORE
WITH CYLINDER DIAL
GAUGE FOR SIZE, TAPER
AND OVALTY
Measurement and
Metrology Lab
Structure
13.1 Introduction
Objectives
13.2 Materials Required
13.3 Devices and Accessories Required
13.4 Experiment Sequence
13.5 Procedure
13.6 Precautions
13.1 INTRODUCTION
The cylinder dial gauge has to have three contact points along the cylinder walls, such
that spindle contact is at 90o to the centre line of the bore and the reading taken is correct.
To ensure this position, the dial gauge is provided with a slider plate. In case dial gauge
is not positioned correctly, this slider plate will go out of contact and will serve as a
warning to the dial gauge user to position the dial gauge correctly in the bore.
The cylinder bores, which are measured, are used in I.C Engines, hence we have to be
very careful while taking reading for taper and ovalty especially.
Objectives
After performing this experiment, you should be able to
•
familiarise with the use of different accessories of the gauge,
•
know its dial reading + and – pre loading and zeroing of the dial,
•
measure the size of the bore, its taper and ovalty, and
•
decide suitability of the bore as per given specifications.
13.2 MATERIALS REQUIRED
(a)
Cylinder dial gauge, and
(b)
Cylinder bore.
13.3 DEVICES AND ACCESSORIES REQUIRED
(a)
A piece of muslin cloth or like.
(b)
A piece of paper and pencil.
43
Laboratory-IV
Figure 13.1 : Ball-type Plug Gauge
Figure 13.2 : A Simple Method of Bore Measurement
13.4 EXPERIMENT SEQUENCE
(a)
Look at the cylinder bore and roughly estimate its diameter.
(b)
With the help of dial gauge distance pieces, measure the bore approximately
(the size of the distance pieces is stamped on them).
(c)
Fit a correct size spindle (size known at step (b) above) with the dial gauge.
(d)
See for general working of the dial gauge by pressing its spindle gently and
seeing the needle.
(e)
See that dial needle goes both sides + and –.
(f)
Rotate dial, so as to ascertain that it can be brought to ‘0’ position, before
actual measurement of the bore is taken.
(g)
With a piece of cloth, clean dial gauge spindle tips and the cylinder bore.
13.5 PROCEDURE
44
(a)
Hold dial gauge vertical and put it into the cylinder such that spindle and
slider plate touch the cylinder walls.
(b)
Slightly move the gauge vertically to and fro and note for mean positions of
the dial needle and the contact of slider plate and spindle.
(c)
In this position rotate the dial and fix its ‘0’ position.
(d)
The portion of the bore at which the dial gauge is ‘0’ is the ridge portion,
where piston has never worked; as such the size of the bore is the original
size, standard size or zero size. Take out the dial gauge, and put in its,
distance piece holder and fix only those distance pieces, such that needle
reads ‘0’. Now this size indicated by distance pieces is the size of the bore.
(e)
Measure taper of the bore by taking one reading at the top of the bore, below
ridge portion.
(f)
Put the gauge further down in the bore and take another reading.
(g)
The difference between the readings at (e) and (f) has a direct bearing on the
taper of the bore.
(h)
For measuring ovalty of the bore, put dial gauge in the bore, just above its
middle point on non-thrust side and take the reading.
(i)
Put dial gauge as at (h) at ‘0’ but on thrust side of the bore and take a
reading. The difference between the readings at (g) and (i) is the ovalty of
the bore.
Measurement and
Metrology Lab
13.6 PRECAUTIONS
(a)
Dial gauge tips and bore should be cleaned before reading is taken.
(b)
Make sure that slider plate always remains in contact with cylinder wall.
(c)
Do not tilt the dial gauge.
45
Laboratory-IV
EXPERIMENT NO. 14 : MEASUREMENT OF ANGLE
WITH SINE BAR AND
HEIGHT GAUGE
Structure
14.1 Introduction
Objectives
14.2 Instruments Used
14.3 Working Principle
14.4 Procedure
14.5 Sources of Error
14.6 Precautions
14.1 INTRODUCTION
The sine bar is one of the most widely used instruments for precision measurement of
angles. It consists of a rectangular section bar of suitable grade steel having accurately
ground pins of equal diameter, one at each end and lying on a line parallel to the axis of
the bar. The distance between the centers of these pins is arranged to be a standard, either
5″, 10″ or 15″ or 125 mm, 200 mm, 500 mm etc.
The sine bar is based on the principle that in a right angled triangle the length of
hypotenuse is kept constant. The sine of different angles can be obtained simply by
varying the length of the perpendicular as shown in Figure 14.1.
sin θ =
h
l
A sine bar is made up of a hardened steel beam having a flat upper surface. The bar is
mounted on two cylindrical rollers. These rollers are located in cylindrical grooves
specially provided for the purpose. The axes of the two rollers are parallel to each other.
They are also parallel to the upper flat surface at an equal distance from its. In this
experiment, you will be introduced to the measurement of angles with sine bar.
Objectives
After performing this experiment, you should be able to
•
develop skill to use sine bar for measuring the external taper angles
accurately (by using a single trigonometrical parameter, i.e. sine of an
angle), and
•
develop skill for setting the job and instruments and observing the readings
correctly.
14.2 INSTRUMENTS USED
A tapered surface of workpiece having good surface finish.
Devices and Accessories Required
46
(a)
Sine bar,
(b)
Surface plate,
(c)
Height gauge,
(d)
Angle plate, and
(e)
Measurement and
Metrology Lab
Square blocks.
14.3 WORKING PRINCIPLE
It is based on trigonometric function sin = side opposite angle/hypotenuse.
Top Flat
Surface
h
Steel Beam
d
L
Rolle
Figure 14.1 : Sine Bar
Sine Bar
L
h
θ
Gauge
Blocks
h
Figure 14.2 : Use of Sine Bar for Angle Measurement
14.4 PROCEDURE
(a)
Clean the surface plate.
(b)
Clean the sine bar.
(c)
Clean the workpiece, and ensure that there are no damages and burrs on the
surfaces of workpiece.
(d)
If there are any burrs remove them by means of oilstone.
(e)
Place the workpiece on surface plate with taper surface facing the surface
plate.
(f)
Place the sine bar on tapered surface of workpiece with the rollers of sine
bar in upward direction.
(g)
Clean the base of height gauge properly.
(h)
Mount the dial indicator on the height gauge.
(i)
Set the dial indicator on the highest point of one of the sine bar roller and
put some pressure on dial indicator.
(j)
Note the reading of dial indicator and height gauge scale.
(k)
Set the dial indicator on second roller of sine bar.
(l)
Bring the same reading on dial indicator by adjusting the height gauge.
(m)
Note the reading of height gauge at the highest point of both the rollers of
sine bar.
(n)
Calculate the difference of two height gauge readings, which will give the
height (h) of one roller with respect to other.
(o)
The centre distance between the two rollers is known for a standard sine bar.
47
Laboratory-IV
(p)
Divide the height in step (n) by centre distance between two rollers. This
h
will give the sine of taper angle sin θ = .
l
(q)
Using sine tables the value of taper angle can be calculated.
14.5 SOURCES OF ERROR
(a)
Improper cleaning of instruments or workpiece.
(b)
Damaged instruments and damaged workpiece surface.
(c)
Improper setting of instrument.
(d)
Initial error in measuring instrument.
(e)
Wrong observation of height gauge measuring head.
(f)
Uneven pressure at two points of reading may lead to error.
14.6 PRECAUTIONS
(a)
All the instruments should be cleaned properly.
(b)
Any burrs and damage on workpiece surfaces should be rectified.
(c)
Zero error in any instrument likely to be checked and if so correct it.
(d)
In case of circular workpiece sine bar should be clamped firmly with the
angle plate.
EXPERIMENT NO. 15 :CHECK THE ANGLES OF
TEMPLATE GAUGE FOR
48
LATHE TOOL/DRILL BIT
ANGLES MADE IN FITTING
SHOP
Measurement and
Metrology Lab
Structure
15.1 Introduction
Objectives
15.2 Instruments Used and Specifications
15.3 Procedure
15.4 Conclusion
15.5 Evaluation
15.6 Sources of Error
15.1 INTRODUCTION
Tool angles are specified for machining of jobs. Tool angles depend on job material,
operation, cutting tool material and volume of material removed/minute. The tool after
grinding and regrinding is checked by a template, having angle grooves of standard
profiles for accuracy of grinding. The tool angles are cut as V grooves in a sheet metal of
12-16 gauge steel as a fitting job and the angles are marked by punch marks.
These templates are projected on a screen and the profile is compared with an accurately
drawn profile on a transparency (or on a sheet on which the profile is projected).
Thus, a template can be checked for accuracy so that it can be used in machine shop for
checking the tool angles after grinding.
In this experiment, you will be introduced to the measurement for checking the angles of
template gauge for lathe tool/drill bit angles made in fitting shop.
Objectives
After performing this experiment, you should be able to
•
develop skill in finding accuracy of angles of template by comparison
through magnification.
15.2 INSTRUMENTS USED AND SPECIFICATIONS
Optical/Profile projector magnification 10 – 100.
Screen 300 × 300 mm or overhead Projector vernier bevel protractor.
Work/Jobs piece – Template gauge – lathe tool, angle gauge and drill angle gauge.
Least Count/minimum reading of vernier bevel protractor 0o–5′.
15.3 PROCEDURE
(a)
Place the template in position.
(b)
Switch on the projector.
(c)
Adjust the position of template to a convenient position.
(d)
Focus the shadow on the screen.
(e)
Make sure that the shadow is not distorted.
(f)
Make the outlines with pencil taking due care.
49
Laboratory-IV
(g)
Remove the sheet and measure angles using vernier bevel protractor and
check by using trigonometric functions.
Reading Taken
Drill point angle depends on material to be drilled.
MS/CI
118o
Aluminum 140o
15.4 CONCLUSION
It is necessary for any template to be checked for accuracy, and the inaccuracies in
grinding tool will result in an inefficient operation in production.
15.5 EVALUATION
How accurate is the comparison of angle on drawing sheet with projected image of
template.
15.6 SOURCES OF ERROR
50
(a)
V-grooves not having straight sides.
(b)
Error in measurement on transparency.
(c)
Screen of projector not aligned to reference screen.
(d)
Distortion of image on screen.
(e)
Error in marking on the drawing sheet.
(f)
Image not sharp due to the thickness of template.
EXPERIMENT NO. 16 :MEASUREMENT OF WORN
OUT IC ENGINE PISTONS
Measurement and
Metrology Lab
Structure
16.1 Introduction
Objectives
16.2 Instruments Used and Specifications
16.3 Devices and Accessories Required
16.4 Procedure
16.1 INTRODUCTION
Piston in automobile engines are to seal the gases on top of cylinder and partition the
cylinder in two portions for different functions in various strokes. It means that it has to
work like a plug with a minimum running clearance between it and the cylinder, so that
the expansion due to heat generated during firing stroke of the engine is accommodated
in the clearance. Normally this clearance between piston and cylinder is 0.075 mm or
0.003″ for aluminum alloy pistons and cast iron pistons. It means that the piston has to be
of the same size as that of cylinder. During the process of engine overhaul, we have to
ascertain whether same old piston can work in the cylinder, that is why the worn out
piston is to be measured for its serviceability. The simplest method of measuring a piston
is with the help of an ottometer. The ottometer measures pistons, rings and gudgeon pins
within a shortest possible time without much adjustment in it. Minimum reading in this
gauge is 50 mm and it can be zeroed with a nut provided.
In this experiment, you will be introduced to the measurement of worn out pistons.
Objectives
After performing this experiment, you should be able to
•
measure a worn out piston with the help of ottometer.
16.2 INSTRUMENTS USED AND SPECIFICATIONS
Worn out pistons with standard specifications.
16.3 DEVICES AND ACCESSORIES REQUIRED
(a)
(b)
Ottometer,
Feeler gauge, 0.15 mm
Minimum reading, 50 mm.
16.4 PROCEDURE
(a)
(b)
(c)
(d)
(e)
(f)
Place the ottometer in a suitable place and see that its knobs and measuring
band is working. Also see that its scale has been perfectly zeroed.
Place worn out piston in the space within the measuring band.
Rotate band knob, such that measuring band tightens around piston.
Lock the band knob.
Peep through magnifying glass window and note the reading. This is the size
of the piston. Compare with the specification given.
Insert 0.15 mm feeler gauge in the top rings land with a new ring. It should
not go.
51
Laboratory-IV
EXPERIMENT NO. 17 :MEASUREMENT OF
CLEARANCE BETWEEN
BORE AND SHAFT WITH
THE HELP OF
PLASTIGAUGE AND FLAT
GAUGES
Structure
17.1 Introduction
Objectives
17.2 Instruments Used and Specifications
17.3 Devices and Accessories Required
17.4 Working Principle
17.5 Procedure
17.6 Precautions and Care of Instruments
17.1 INTRODUCTION
In this experiment, you will be introduced to the measurement of clearance between bore
and shaft with the help of plastigauge and flat gauges.
Objectives
After performing this experiment, you should be able to
•
measure clearance between two mating surfaces (crank shaft and main
bearing), and
•
know precise use of plastigauge and flat gauge.
17.2 INSTRUMENTS USED AND SPECIFICATIONS
(a)
A packet of plastigauge.
(b)
Flat gauges in the sizes of 0.001″, 0.002″, 0.003″ and 0.005″ or 0.01 mm,
0.02 mm and 0.03 mm.
(c)
A piece of cloth.
17.3 DEVICES AND ACCESSORIES REQUIRED
A shaft or a crankshaft of automobile engine fitted into bores or main bearing of
automobile engine.
17.4 WORKING PRINCIPLE
When the fit between shaft and hole is tight-fit, the shaft will not rotate easily but if it is
loose fit so that, it will rotate easily. The working of these gauges depend upon this
principle.
52
17.5 PROCEDURE
Measurement and
Metrology Lab
Flat Gauge
(a)
Wipe and clean both the surfaces of crankshaft and main bearing.
(b)
If the specified clearance between crankshaft and main bearing is 0.002″
take a flat gauge of 0.002″.
(c)
Put this flat gauge between the crankshaft and main bearing.
(d)
Tighten the nuts of the bearing one after the other slowly and gradually, till
these are tightened to the specified torque.
(e)
Try to rotate crankshaft either side.
(f)
If the crankshaft rotates with a slight drag and a normal manual force, the
clearance is correct to 0.002″. If it does not rotate at all, the clearance is less
than two thousandth of an inch. If it rotates more freely, the clearance is
more than 0.002″.
(g)
If it is required to know the exact clearance try for other sizes of flat gauges
and repeat the process as mentioned in (d), (e) and (f) above.
Plastigauge
(a)
Put a suitable plastigauge in between crankshaft and main bearing.
(b)
The size of the plastigauge should be little less say 2 to 3 mm than the
bearing width.
(c)
Tighten bearing nuts one after the other slowly and gradually till specified
torque is reached in the nuts.
(d)
Now loosen the nuts, take out pressed plastigauge.
(e)
Measure the thickness of plastigauge on the markings given on plastigauge
packet.
(f)
If the thickness coincides with the clearance specified, it is correct, if less or
more, still the clearance can be known from the width of the plastigauge
where it coincides.
17.6 PRECAUTIONS AND CARE OF INSTRUMENTS
(a)
Do not rotate crankshaft when using a plastigauge for measurement.
(b)
If the thickness of plastigauge is not regular throughout its length, crank pin
is tapered.
(c)
When using flat gauge, do not turn crankshaft more than 2 rotations on
either side, otherwise the shim strip will embed.
53
Laboratory-IV
EXPERIMENT NO. 18 :ALIGNMENT TESTS OF
LATHE
Structure
18.1 Introduction
Objectives
18.2 Instruments Used and Specifications
18.3 Procedure
18.1 INTRODUCTION
For metrology purposes, the term alignment refers to two axes merging in each other or
one axis extending beyond the other.
Two lines of axes are said to be in alignment when their distance apart at several points
over a given length is measured and this distance does not exceed a given standard
tolerance.
The dimensions of a gauge, its surface finish, geometry and accurate production of
components/parts depend upon the inherent quality and accuracy of the machine tools
used for its manufacture. Therefore for maintaining the accuracy of the components
within prescribed limits, the machines should be properly aligned as the quality of
workpieces depend upon :
(a)
Stiffness and rigidity of the machine tool and its component parts.
(b)
The alignment of various machine parts in relation to each other. This is
very important because the geometry of various shapes is based on the
relative motions between various machine parts and hence on alignment of
various parts.
(c)
The quality and accuracy of the control devices and driving mechanism.
In most cases the machining of a given geometric surface is achieved through a
combination of work tool movements and the accuracy of the surfaces generated depends
on the accuracy of the mating elements present in the machine tool. The various tests
applied to any machine tool could be grouped below :
54
(a)
Tests for the level of installation of machine in horizontal and vertical
planes.
(b)
Tests for flatness of machine bed and for straightness and parallelism of bed
ways or bearing surfaces.
(c)
Tests for perpendicularity of guide ways to other guide ways or bearing
surfaces, which support motion in cross direction.
(d)
Tests for true running of the main spindle and its axial movements.
(e)
Tests for parallelism of spindle axis to guideways or bearing surfaces.
(f)
Tests for the line of movement of various members, e.g. saddle and table
cross slides etc. along their ways.
(g)
Practical tests in which some test pieces are machined and their accuracy
and finish is checked.
Measurement and
Metrology Lab
Objectives
After performing this experiment, you should be able to
•
develop skill for performing alignment tests on various machine tools,
•
impart an up-to-date knowledge of need of alignment in machine tools,
•
explain the relationship of controlled movement of any component with
respect to some other component, and
•
understand the effects of misalignment of any component on the
performance of the machine.
18.2 INSTRUMENTS USED AND SPECIFICATIONS
A lathe in good working condition with all standard accessories, i.e. live and dead
centres, sleeve etc.
(a)
Dial indicator,
(b)
Dial stand with magnetic base,
(c)
Flexible dial stand,
(d)
Parallel blocks,
(e)
Straight edge,
(f)
Straight bar,
(g)
Standard test mandrel,
(h)
Straight spirit level,
(i)
Box type spirit level,
(j)
Alignment microscope,
(k)
Taut wire,
(l)
Set of spanners,
(m)
Mandrel and centre draw bar.
Figure 18.1 : Trucing Up of Work in Lathe
55
Laboratory-IV
18.3 PROCEDURE
(a)
Clean all surfaces perfectly on which alignment tests are to be performed.
(b)
Level the bed of lathe for longitudinal as well as cross directions.
(c)
Follow the test chart for performing different alignment tests.
Figure 18.2 : The Test for Parallelism of Spindle with Bed, using a
Mandrel Inserted in the Centre Hole
Figure 18.3 : Testing for Capability of a Lathe to Turn Parallel; an Accurate Mandrel being Placed
between Centres and a Dial Indicator Run Along by the Slide Rest
Figure 18.4 : Indicator Held in Slide Rest to Ascertain Truth of Faceplate
56
EXPERIMENT NO. 19 :STUDY AND USE OF
COMPARATORS
Measurement and
Metrology Lab
Structure
19.1 Introduction
Objectives
19.2
19.3
19.4
19.5
19.6
19.7
Instruments Used and Specifications
Working Principle
Procedure
Conclusion
Precautions
Sources of Error
19.1 INTRODUCTION
In various production and other situations for assembly, matching of parts etc., it is not
necessary to know the exact absolute dimensions of a job. If it is known what deviation
of measurement is there from a standard, we may decide whether the sample is
acceptable for selective assembly or interchangeable assembly.
The comparator is a device, which takes a dimension of standard job as reference
dimension, and gives a reading through a pointer on a scale, which is the variation in
such dimension of the job.
Objectives
After performing this experiment, you should be able to
•
use comparators and develop skill in using them.
19.2 INSTRUMENTS USED AND SPECIFICATIONS
Mechanical comparator-Sigma Comparator 0-150 mm range for pointer, scale 0.25 mm
from centre, div. of scale 10, permissible error 10, magnification 3000.
Slip Gauge Set
Work pieces-Any 10 jobs of size within the range of comparator and master jobs.
19.3 WORKING PRINCIPLE
Figure 19.1 gives the constructional details of sigma mechanical type comparator. A
vertical beam is mounted on flat steel spring A connected to fixed member which in turn
is screwed to a back plate. The assembly provides a frictionless movement with a
restraint from the springs. The shank B at the base of the vertical beam is arranged to take
a measuring contact, selected from available range. The stop C is provided to restrict
movement at the lower extremity of the scale. Mounted on the fixed member is the
hinged assembly D carrying the forked arms E. This assembly incorporates a hardened
fulcrum (provided with means for adjustment of controlling the ratio of transmitted
motion) operative on the face of a jeweled insert on the flexible portion of the assembly.
The metal ribbon F, attached to the forked arms passes round the spindle G causing it to
rotate in especially designed miniature ball bearings. Damping action to the movement is
effected by a metal disc, mounted on the spindle, rotating in a magnetic field between a
permanent magnet and a steel plate. The indicating pointer H is secured to boss on the
disc. The trigger J (opposite K) is used to protect the measuring contact. At the upper end
of the vertical beam, an adjusting screw is provided for final zero setting of the scale. A
new-patented feature is shown at K. This is a magnetic counter balance, which serves to
neutralize the positive ‘rate’ of spring reaching on the measuring tip. In this way a
constant pressure over the whole scale range is achieved. The instrument is available with
57
Laboratory-IV
vertical capacities of 6″, 12″ and 24″ and magnification of 500, 1000, 1500, 3000 and
5000. The scales are graduated both in English and Metric systems. The least count is of
the order of 10 to 100 thousandth of an inch.
A
E
F
D
H
G
C
J
K
A
B
Figure 19.1 : Sigma Comparator
A worktable on the base of this comparator stand is used to keep the job on. Special
attachments are used for typical jobs like screw thread effective/outside diameter.
Figure 19.2 gives the pictorial view of dial indicator type of mechanical comparator. It
consists of a sensitive dial indicator mounted on a horizontal arm on a stand. The arm is
capable of coarse and fine adjustment movements in the vertical direction for initial
setting of the instrument. The base is heavy so that stability and rigidity of the instrument
is ensured. Different attachments are available depending upon the type of job.
Output
Displacement
x
Scale
Reeds
R2
Reeds R1
Movable
Member
A
B
Fixed
Member
x (Input Displacement)
Component
Figure 19.2 : Mechanical (Reed) Comparator
58
19.4 PROCEDURE
(a)
Clean the comparator with flannel cloth or chamoise leather.
(b)
Wipe the standard job clean of dust etc.
(c)
After lifting anvil by pressing the trigger, mount the standard jobs/slip
gauges on the work table.
(d)
Adjust the screw at the top of vertical beam to zero pointer reading.
(e)
Replace the standard job with sample job and record the reading on scale.
(f)
Repeat the comparisons for rest of sample jobs. Classify the jobs into
acceptable/not acceptable and give code number for selective assembly.
Measurement and
Metrology Lab
19.5 CONCLUSION
Instead of making absolute measurement we can easily know whether job is within two
limits to classify the sample and give code symbol for selective assembly or reject it.
19.6 PRECAUTIONS
(a)
Cleanliness of measuring instrument and job.
(b)
Zero error (w.r.t. std. job).
(c)
Friction in mechanism not permitting anvil in contact with job.
(d)
Calibrations of the comparator.
19.7 SOURCES OF ERROR
(a)
Foreign particles between anvil and job.
(b)
Zero adjustment out.
(c)
Error in master.
(d)
Wornout components due to friction in mechanism.
(e)
Anvil not exerting correct pressure on jobs.
59
Laboratory-IV
EXPERIMENT NO. 20 : STUDY AND USE OF TOOL
ROOM MICROSCOPE
Structure
20.1 Introduction
Objectives
20.2 Instruments Used, Specifications and Materials
20.3 Brief Description of Instrument
20.4 Procedure
20.5 Precautions
20.1 INTRODUCTION
Engineering microscopes designed to satisfy various measuring needs of toolmaker’s are
known as toolmaker’s microscopes. A plain toolmaker’s microscope is primarily
intended for a particular application. On the other hand, universal toolmaker’s
microscope is adaptable to an uncommonly wide range of measuring tasks. A
toolmaker’s microscope is designed for measurements of parts of complex forms, e.g.
profile of external threads, tools, templates and gauges. It can also be used for measuring
centre-to-centre distance of holes in any planes, as well as the co-ordinate of the outline
of a complex template gauges.
Objectives
After performing this experiment, you should be able to
•
appreciate the importance of precision measurement,
•
know how precise measurements can be taken with this instrument,
•
explain the field of application/working of this instrument, and
•
understand the principle of working of tool room microscope.
20.2 INSTRUMENTS USED, SPECIFICATIONS AND
MATERIALS
(a)
A rectangular MS piece with two marked points.
(b)
A threaded bolt with standard thread form.
(c)
Tool room microscope, light connections, magnification 10 x and 20 x.
20.3 BRIEF DESCRIPTION OF INSTRUMENT
It consists of optical head, which can be adjusted vertically along the ways of the vertical
column and can be clamped in any position. The working table is secured on a heavy
hollow base. The table has a compound slide to give longitudinal and lateral movements
actuated by accurate micrometer screws having thimble scales and vernier. At the back of
the base is a light source, which provides a horizontal beam of light reflected upwards by
90o towards the table. This beam of light passes through a transparent glass plate on
which flat parts to be checked are placed. A shadow image of the outline of the contour
passes the objective of the optical head and is projected by a combination of three prisms
to a ground glass screen. Observations are made through the eyepiece of the optical head.
Figure 20.1 gives the views of a tool room microscope.
60
Vertical
Column
Eyepiece
Measurement and
Metrology Lab
Optical Head
Table
Cross Slide
Micrometer
Front Slide
Micrometer
Figure 20.1 : Tool Room Microscope
Cross lines are engraved on the glass screen, which can be rotated through 360o, and
these lines make the measurements. The angle of rotation of screen can be read on the
optical head. The eyepiece field of view contains an illuminated circular scale with a
division value of one minute. Adjusting optical head tube performs focussing.
20.4 PROCEDURE
(a)
The relative positions of two or more points on a workpiece are determined
by measuring the travel of the work table necessary to transfer a second
point to the position previously occupied by the first and so on.
(b)
Angles are measured by successively setting fiducially situated line in the
focal plane of the eyepiece along with arm of the image of the angle, or
through points indicating the angle and noting from a protractor scale the
angle through which the fiducial line has turned.
(c)
The thread forms can be compared with the outline on a glass template
situated at the focal plane of microscope eyepiece. Measurement of
discrepancies can be made from the projected thread form and template.
(d)
Comparison of the enlarged projected image with a tracing drawn on exact
number of times full size and affixed to the projection screen.
20.5 PRECAUTIONS
(a)
To avoid backlash error the table screws must be moved in one direction
only while measuring.
(b)
Fiducial line must be set parallel with the axis of movement of table, before
measurements.
61
Laboratory-IV
FORMAT OF THE COVER PAGE
TITLE (COVER) PAGE
BMEL-004 : Lab. Exp. Report (Experiment #
………………………. )
On
“
Section No.
“
Date :
/
By
(1)
Name :
(2)
Name :
(3)
Name :
Date :
62
/
LABORATORY REPORT FORMAT
Measurement and
Metrology Lab
BMEL-004 : METROLOGY AND INSTRUMENTATION
Abstract
A brief description of the overall idea of the experiment and the most important
results.
Objectives
Briefly state the objectives of the experiment in your own words.
Experimental Procedure
Explain the experimental procedure, step-by-step, in your own words, listing the
test equipment, instruments, tools, materials, cutting parameters, etc. used.
Test Results
Present the test results using graphs and/or tables to explain them. Follow the
general/standard conventions for figures and tables. The original data sheets,
computation sheets and other appropriate materials are to be included as
appendices.
Discussion
Discuss the best results (referring to specific figures and tables). Be sure to discuss
the results in comparison with existing theories, other references, etc. Also discuss
probable sources of experimental error and how (if possible) they can be
eliminated.
Conclusions
A brief summary of the experiment, test results and conclusions drawn from the
experiment. Also suggestions/recommendations for improving the design and
execution of the experiment may be included.
References
List all references used for the preparation of the report.
63
Laboratory-IV
FURTHER READINGS
Thomas G. Beckwith and John H. Lien Lard, Mechanical Measurement, 2nd Edition,
John Willey and inc. Co., Singapore.
Holman J. P., Experiment Methods for Engineer. 10th Edition, Tata McGraw Hill, New
Delhi.
Raghuwashi B. S., Workshop Technology, 15th Edition, Dhanphat Rai and Co., New
Delhi.
Hazra and Choudhary, Workshop Technology, Volume I, Media Promoters and
Publication Pvt. Ltd. Mumbai.
Jain R. K., Engineering Metrology, Khanna Publishers, New Delhi.
Kapoor A. C., Workshop Practical Manual, Dhanpat Rai and Co., New Delhi.
Shawne A. K., Mechanical Measurement and Instrumentation, Dhanpat Rai and Co. (P)
Ltd.
Krar Steve F, Technology of Machine Tools, McGraw-Hill International.
Francis T. Farago, Mark A. Kartis, Handbook of Dimensional Measurement, Industrial
Press Inc.
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Measurement and
Metrology Lab
LABORATORY-IV
In the field of engineering and technology, Laboratories play a very important role to
understand the complex natural phenomena and very often are the only source of
scientific knowledge in solving complex practical problems. For clear and better
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Laboratory-IV
understanding of the theory, the laboratory practice occupies very important status in the
engineering curriculum. With the advancement in instrumentation, the laboratory practice
has become more sophisticated and specialized. Thus, Laboratory forms an integral part
of the basic courses. A proper training in the science of measurement and use of
measuring instruments is essential for students of engineering and technology.
Laboratory experiments create a physical contact with the various types of behaviour of
nature and help to understand its working.
This block on Laboratory-IV consists of twenty experiments. All these experiments are
based on the topic of Metrology and Instrumentation. This block has been designed to
give a complete understanding of experimental methods of Metrology and
Instrumentation.
Description of each experiment includes the objectives, theory, a brief description of the
experimental setup, procedure for conducting the experiment and the tables for
observations and computations.
General guidelines are included for the benefit of the learners. They are advised to refer
to the relevant text before performing the experiments and to make the best use of the
time allocated for the laboratory.
Engineering metrology is defined as the measurement of dimensions : length, thickness,
diameter, taper, angle, flatness, profiles and others. As an example, consider the part
shown in figure below.
l1
r
α
l3
l2
The dimensions that are measured are marked as l1, l2, l3 (length), α (angle) and
r (radius).
The newer trend in measurement is to measure dimensions “on line”, during
manufacturing or in process. An important feature of metrology in process of
manufacturing is to check dimensional tolerances, i.e. permissible variation in
dimensions of part. Tolerances play important role in assembly, interchangeability of
parts and functioning of machines and products. They also have visible impact on
economy or manufacturing costs. The smaller tolerances lead to higher manufacturing
costs. The linear dimensions are crudely measured by ruler scale which carries lines (or
divisions) at certain distance apart. But various instruments have now been developed
which increase the accuracy, sensitivity (resolution) and precision of measurement.
Sensitivity or resolution is defined as the smallest difference in dimensions that the
instrument can detect or measure.
Precision is defined as the degree to which the repeated results are obtained on the same
dimensions by the instrument. The instrument parts may be affected by such variables as
temperature whereby the precision may be affected.
Accuracy is the difference between the measured and actual value of a dimension. The
smaller this difference, higher is the accuracy. Accuracy and sensitivity are not to be
confused.
METROLOGY AND INSTRUMENTATION
LABORATORY
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The aim of this laboratory is to make the students understand the importance of precision
measurements and to familiarize them with the art of measurement. In view of its
industrial relevance, Metrology and Instrumentation laboratory has special importance in
engineering programme. In this laboratory, exposure to high precision measuring
instruments is provided, to make them familiar with principles, operation and application
of measuring techniques.
Measurement and
Metrology Lab
The manual gives basic description of laboratory exercises and experiments in the areas
of Metrology and Instrumentation for BMEL-004 – Metrology and Instrumentation. The
exercises provide an opportunity for hands-on experience and experimentation in the
important areas of mechanical measurement and metrology.
It is highly recommended that you read over the description of the exercise or experiment
and the related material in your blocks of BME-014, i.e. Metrology and Instrumentation,
before coming to the lab sessions. This will enable you to make more effective use of the
time available and generate more reliable data for your reports.
We hope that you enjoy the experience and take the fullest advantage of it.
The laboratory is equipped with following equipments :
•
Profile projector
•
Floating carriage diameter measuring machine
•
Tool maker’s microscope
•
Slip and angle gauges
•
Complete range of hand held precision measuring instruments
•
Electronic and pneumatic gauges
This block introduces you to the Laboratory-IV, which deals with the experiments on
Metrology and Instrumentation. In total, twenty experiments are prescribed. Students are
expected to perform minimum 10 experiments out of the suggested list.
LIST OF PRACTICAL EXPERIMENTS
Experiment 1
Measurement with scale and vernier calipers.
Experiment 2
Measurement with micrometers – external and internal.
Experiment 3
Measurement with height and depth gauge.
Experiment 4
Measurement with dial indicator using surface plate and accessories
for (a) flatness, (b) concentricity of ground jobs.
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Laboratory-IV
Experiment 5
Measurement with combination set.
Experiment 6
Measurement of angles with bevel protractor.
Experiment 7
Study and use of slip gauges.
Experiment 8
Measurement of thread characteristics.
Experiment 9
Marking and measuring exercise with all measuring devices.
Experiment 10
Study of inspection gauges such as plug, snap and thread gauges.
Experiment 11
Measurement of tapers – external, internal.
Experiment 12
Measurement of spur gear characteristics.
Experiment 13
Measurement of bore with cylinder dial gauge for size, taper and
ovalty.
Experiment 14
Measurement of angle with sine bar and height gauge.
Experiment 15
Check angles of template gauge made in the fitting shop
(for lathe tool angle and drill bit angle).
Experiment 16
Measurement of worn out IC Engine piston.
Experiment 17
Measurement of clearance between bore and shaft with the help of
plastigauge and flat gauges.
Experiment 18
Alignment tests of lathe.
Experiment 19
Study and use of comparators.
Experiment 20
Study and use of tool room microscope.
Note : Students are expected to perform minimum 10 experiments out of the above
suggested list.
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