K.G Reddy College of Engineering...

K.G Reddy College of Engineering Technology (Chilkur Village, Moinabad Mandal, R.R- District, T.S - 501504)

DEPARTMENT OF MECHANICAL ENGINEERING

ENGINEERING METROLOGY LAB

S.NO NAME OF THE EXPERIMENT PAGE NO

1 USE OF GEAR TEETH VERNIERS CALIPER

AND CHECKING THE CHORDAL ADDENDUM

AND CHORDAL HEIGHT OF SPUR GEAR

1

2 MACHINE TOOL ALIGNMENT TEST ON THE

LATHE

4

3 TOOL MAKERS MICROSCOPE AND ITS

APPLICATION

7

4

ANGLE MEASUREMENT BY BEVEL

PROTRACTOR

8

MEASURING OF TAPER ANGLE BY SINE BAR 9

5 USE OF SPIRIT LEVEL AND OPTICAL FLATS

IN FINDING THE FLATNESS OF SURFACE

PLATE.

10

6 THREAD MEASUREMENT BY TWO/THREE

WIRE METHOD

11



B.Tech. III Year I Sem. L T/P/D C

Course Code: ME507PC 0 0/3/0 2

Objectives:

• To import practical exposure to the metrology equipment

• To conduct experiments and understand the working of the same.

Prerequisites: Theoretical exposure to Metrology and machine tools.

1. Use of gear teeth Vernier calipers for checking the chordal addendum and chordal

height of the spur gear.

2. Machine tool alignment of test on the lathe.

3. Tool makers microscope and its application

4. Angle and taper measurements by bevel protractor and sine bars.

5. Use of spirit level and optical flats in finding the flatness of surface plate.

6. Thread measurement by 2-wire and 3-wire methods.



Introduction

Metrology is a science of measurement. Metrology may be divided depending upon the quantity

under consideration into: metrology of length, metrology of time etc. Depending upon the field

of application it is divided into industrial metrology, medical metrology etc.

Engineering metrology is restricted to the measurement of length, angles and other− quantities

which are expressed in linear or angular terms.

For every kind of quantity measured, there must be a unit to measure it. This will enable− the

quantity to be measured in number of that unit. Further, in order that this unit is followed by all;

there must be a universal standard and the various units for various parameters of importance

must be standardized.

It is also necessary to see whether the result is given with sufficient correctness and− accuracy

for a particular need or not. This will depend on the method of measurement, measuring devices

used etc.

Thus, in a broader sense metrology is not limited to length and angle measurement but− also

concerned with numerous problems theoretical as well as practical related with measurement

such as:

1. Units of measurement and their standards, which is concerned with the establishment,

reproduction, conservation and transfer of units of measurement and their standards.

2. Methods of measurement based on agreed units and standards.

3. Errors of measurement.

4. Measuring instruments and devices.

5. Accuracy of measuring instruments and their care.

6. Industrial inspection and its various techniques.

7. Design, manufacturing and testing of gauges of all kinds.

1

ENGINEERING METROLOGY S.Sathish, Asst Professor

EXP 1:

USE OF GEAR TEETH VERNIERS CALIPER AND CHECKING THE CHORDAL

ADDENDUM AND CHORDAL HEIGHT OF SPUR GEAR

AIM: To determine module, pressure angle and Chordal Tooth thickness of the given gear

specimen.

APPARATUS: Vernier Calipers, Gear Tooth Vernier Calipers.

THEORY:

Gear is a toothed wheel, which is used to transmit the motion and power. Involutes profile gears

are widely used compared to cycloidal profile gears. The performance of a gear depends on the

uniform thickness of teeth, concentricity and pitch. The thickness of a gear tooth varies from the

base to tip. Hence to specify the thickness of the tooth pitch circle will be taken as the reference.

The thickness of a gear tooth is defined as the arc distance measured along the pitch circle from

its intercept with one flank to its intercept with the other flank of the same tooth. As the tooth

thickness is defined as the length of an arc, it is difficult to measure directly. In most of the cases

it is sufficient to measure the chordal thickness i.e. the chord joining the intersection of the tooth

profile with the pitch circle. From the figure tooth thickness is specified as an arc distance AEB

and chordal tooth thickness is ADB. d, is called chordal addendum because it is

slightly greater than the addendum CE.

2


The chordal tooth thickness can be very conveniently measured by a gear tooth vernier (Shown

in fig.). Since the gear tooth thickness varies from the tip to the base circle of the tooth, the

instrument must be capable of measuring the tooth thickness at a specified position on the tooth.

Further this is possible only when there is some arrangement to fix that position where the

measurement is to be taken. The gear tooth vernier has two vernier scales and they are set for the

width ‘w’ of the tooth and the depth‘d’ from the top at which ‘w’ occurs.

PROCEDURE:

(1) Module (m): Count the number of teeth on the given gear specimen and measure its

outer diameter with the help of vernier calipers. Then find out the module by the

following relation.

Addendum circle diameter = m (T+2)

Where m = module

T = no. of teeth

Find the pitch circle diameter Dp by the relation m = Dp/ z

(2) Chordal tooth thickness (w):

First calculate the value of chordal addendum‘d’ by the formula:

Set the vertical scale of the Gear tooth vernier equal to Chordal addendum, then adjust the

horizontal scale in such a way that the tips of two jaws of vernier touch exactly at the

intersections points of pitch circle and two opposite flanks as shown in the figures. The reading

of horizontal scale of the gear tooth vernier is the measured value of chordal tooth thickness.

Theoretically

3


Theoretically w = m T sin (90/ T)

Compare the values of chordal tooth thickness theoretically and practically. Find out the

percentage.

RESULT:

Module of the gear:

Chordal Tooth thickness:

Chordal height of the gear:

4


EXP 2: MACHINE TOOL ALIGNMENT TEST ON THE LATHE

AIM:

To perform machine tool alignment test on the lathe machine.

APPARATUS:

Spirit level, gauge blocks, dial gauge

THEORY:

The surface components produced by machining processes are mostly by generation. As a result,

the quality of surface produced depends upon the accuracy of the various movements of the

machine tool concerned. It therefore becomes important to know the capability of the machine

tool by evaluating the accuracy of the various mechanisms that are directly responsible for

generating the surface. For this purpose a large variety of tests have been designed.

MEASURING INSTRUMENTS USED FOR TESTING:

The accuracy of the machine tools employed should be higher than the accuracy of the

components that it produces. Similarly the quality of the measuring equipment used for machine

tool testing should be commensurate with the quality expected from such testing. A few

commonly used equipments are

• Dial Indicators

• Test mandrels

• Straight edges

• Spirit levels

TEST PROCEDURES:

The major tests that are conducted on machine tool are:

• Testing the quality of the slide ways and the locating surfaces

• Testing the accuracy of the main spindle and its alignment with respect to other parts of the

machine tool.

• Testing the accuracy of the parts produced by the machine tool.

ACCEPTANCE TESTS

Tests that can be conducted on Lathe machine:

1. Quality of slide ways: To test the quality of the slide ways it is necessary to mount the dial

indicator on a good datum surface. Then the plunger is moved along the longitudinal direction

5


of the slide ways which provides an indication of the undulations present on the surface of the

slide ways.

2. Accuracy of the spindle:

These tests are related to the true running of the spindle and the centre located in the spindle

along with the alignment, parallelism and perpendicularity of the spindle with the other axes of

the concerned machine tool.

True running of the centre: The live centre may be loaded into the lathe spindle and a dial

indicator mounted as shown in fig. This test is required only for machines where the work piece

is held between centres. The readings of the dial indicator are taken while rotating the spindle

through full rotation.

True running of the spindle: the taper shank of the test mandrel of about 300 mm length is

mounted into the spindle as shown in fig. The plunger of the dial indicator rests on the

cylindrical surface of the mandrel. The spindle is rotated slowly and the readings of the dial

indicator are noted. The deviation should normally be less than 0.01mm. The test is to be

repeated with the dial indicator positioned close to the spindle bore as well as at the extreme end

of the test mandrel.

Squareness of the face: this test is used to measure the squreness of the shoulder face with

reference to the spindle axis. The plunger of the dial indicator rests on the extreme radial position

of the shoulder face and the reading is taken. It is repeated by slowly rotating the spindle till the

dial indicator comes to a point that is diametrically opposite to the reading taken earlier.

6


3. Alignment tests:

Parallelism and perpendicularity: Parallelism and perpendicularity between two axes or two

surfaces is normally measured in two planes, horizontal and vertical. For this purpose the test

mandrel is mounted in the spindle as shown in fig. with dial indicator mounted on the saddle or

carriage. The plunger of the dial indicator touches the mandrel surface as shown in fig. the saddle

is moved for a specified distance and the dial reading noted. The test is repeated in the horizontal

direction as well.

Parallelism between the outside diameter of the tail stock sleeve and the slide ways as

shown in fig.

Parallelism between the line of centers and the slide ways shown in fig.

RESULT:

7


EXP 3: TOOL MAKERS MICROSCOPE AND ITS APPLICATION

Aim:-

To determine the angle and pitch of given external screw thread

Apparatus:-

Tool maker’s microscope, specimen

Theory:-

The tool maker microscope is designed for measurement of components of difficult forms.

Ex:- profile of external threads, tools , gauge. It can be used for measuring center to center

distance of holes in any plane it consists of optical head which can be adjusted vertically along

inspection the table can be moved in longitudinal direction and lateral direction by micrometer

screws, which are having barrel and thimble at back of base light is arranged which provides on

the optical head. The image of component passes through optical head and observations. The

reading of longitudinal micrometer is noted. The difference gives the pitch of the thread.

Calculations:

Table:

s.no MSR PSR TR MSR PSR TR

Result: - The experiment is conducted on tool makers microscope , the angle, pitch of thread

determined.

Conclusion:-

The pitch of the screw thread =

Angle of external screw thread =

8


EXP 4(A): ANGLE MEASUREMENT BY BEVEL PROTRACTOR

Aim:-

To determine angle of the given specimen using bevel protractor.

Apparatus:-

Bevel protractor, specimen.

Theory:-

It is the simplest for measuring the angle below the two faces of the component

Their consists of protractor which is used to measure the angles

1) Vernier 2) Optical

Vernier bevel protractor:-

It consists of a base plate to the main body and adjustable blade which is attached to the circular

plate. A vernier scale is provided on the main scale the adjustable scale is capable of rotating

freely about the center of the main scale and it can be locked at position by lock nut. It is capable

of measuring 0 to 360 deg. The main scale on the disc is graduated in degrees of arc. The vernier

scale has 12 divisions on each side of centre zero.

Each division on the vernier scale

= 5pow1 of arc which is the least count of vernier scale

The reading of vernier bevel protractor = MSR+(VSR X LC)mm

Optical bevel protractor:-

A recent development of vernier bevel protractor is optical bevel protractor. In this instrument a

glass ole is divided at 10pow1 of arc intervals through out 360deg and this glass ole is fitted

inside the main body. A lens is fitted through which measurements are taken from the glass ole.

With the help of the optical bevel protractor it is possible to read 5pow1 of arc 1.e., LC of this

instrument is 5pow-1

Procedure:-

1. Place the adjustable blade on the component

2. Tight the blade using lock nut

3. Take the main scale reading

4. Take the vernier scale reading from vernier scale which is fixed on the main scale through lens

OBSERVATION TABLE:

S.NO MSR VSC VSR(VSC*L.C) TR(MSR+VSR)

Result:-

The experiment is conducted an optical bevel protractor and angle of given specimen is

determined.

Conclusion:-

The angle of given specimen is………….

9


EXP 4(B): MEASURING OF TAPER ANGLE BY SINE BAR

Aim: To measure the taper angle of a work piece by using sine bar.

Apparatus: Sine bar, Rollers, Slip gauge, Surface Plate, Clamps Lightening work piece, Taper

work pieces.

Principle: Sine bar is based upon laws of trigonometry. To set a given angle one roller of the bar

is placed on the surface plate and the combination of slip gauges is inserted under the second

roller as shown in the figure. If h is the height of the combination of the slip gauges, l is the

distance between roller centers, Then Therefore, θ = sin-1 (h/L) Then the angle can be measured

as a function of sine. Thus, it is called sine bar.

Requirements of a sine bar: The axes of the roller must be parallel to each other and the center

distance L must be known. The size of the bar is specified by this distance. The top surface of the

bar must have a high degree of flatness. The roller must be of identical diameters and round

within a close tolerance. Depending upon the accuracy of the center distance, sine bars are

graded as of A grade or B grade. Sine bars are guaranteed accurately up to 0.02 mm /meter of

length and A grade sine bars are more accurate and guaranteed up to 0.01 mm/meter of length.

Procedure:

1. The sine bar is made to rest on surface plate with rollers contacting the datum.

2. Place the component on sine bar and lock it in position.

3. Lift one end of the roller of sine bar and place a pack of slip gauge, underneath the roller.

Height of the slip gauges (h) should be selected such that the top surface of component is parallel

to the datum plate.

4. Record the final height of the slip gauge combination for achieving parallelism.

5. Calculate inclination θ = sin-1 (h/L)

Limitations:

1. Sine bar is reliable for angles less than 15 degrees, and the angle above 45 degrees.

2. It is physically clumsy to hold in position.

3. Slightly errors of the sine bar cause larger angular errors.

4. Size of the parts which can be impacted by sine bar is limited.

Result: The taper angles of the given work piece as measured by sine bar is ________

10


EXP 5: USE OF SPIRIT LEVELIN FINDING THE FLATNESS OF SURFACE PLATE

Aim:-

To check the flatness of given surface plate

Apparatus:-

Spirit level, surface plate

Theory:-

Generally spirit level is used for leveling the machinery and other instruments. But spirit

levels are also used to measure the angles. It is also called precision level. It consists of

glass tube and of the tube. If the tube is fitted through a small angle if R- radius of tube L

distance of bubble moved when spirit level is fitted to same angle

The angle is calculated as fallows

L=R8,

8=L/R

Procedure:-

1. Keep the spirit level on the surface plate

2. Observe the bubble in the spirit level

3. If bubble is in the middle of spirit level than surface is flat.

4. If bubble is not in the middle of spirit level than surface is not flat

5. Repeat the same procedure at different places of surface plate.

Result:-

The experiment has been conducted on spirit level to check the flatness of given

Surface plate

Conclusion:-

The given surface plate is flat/not flat---------------------

11


EXP 6: THREAD MEASUREMENT BY TWO/THREE WIRE METHOD

Aim: To determine the effective diameter of the given threaded specimen using two/three wire

method.

Apparatus: Set of Wires, Specimen, Digital Micrometer.

Theory:

1. Angle of Thread: This is the angle included between the sides of the thread measured in an

axial plane. It is represented by the letter A. The half angle is represented by the small letter. The

angle of thread is known from the name of the thread. All National form and Unified threads

have a 60 degree angle. Acme and Worm threads have a 29 degree angle, and Whitworth threads

have a 55 degree angle.

2. Pitch: This is the distance from a point on the screw thread to a corresponding point on the

next thread measured parallel to the axis of the thread. It is represented by the letter p.

3. Depth of Thread: This is the distance from the crest or the root of the thread measured

perpendicular to the axis of the screw or nut. It is represented by the letter h.

4. Major Diameter: This is the largest diameter of the screw or nut. It is represented by the

letter D. No formula is needed for the Major diameter as it is used to identify the size of the

screw. For instance a ¼" -20 screw is one having a major diameter of 1/4 inch, and 20 threads

per inch.

5. Pitch Diameter (Effective diameter): The pitch diameter is the diameter where the thread

thickness is equal to the space between the threads. If the flats at the top and bottom of the thread

are the same, the pitch diameter will coincide with the middle of the sloping side of the thread.

The pitch diameter is represented by the letter E.

6. Minor Diameter: This is the smallest diameter of the screw or nut. On the nut it corresponds

to the tap drill size. It is represented by the letter K.

12


7. Lead Angle: This is the angle made by the pitch helix, with a plane perpendicular to the axis.

It is represented by the letter s.

Note: The term LEAD ANGLE is taken from the ASME, Tentative American Standard for

Letter Symbols for Gear Engineering B6.5, 1954, as being preferable to the former term helix

angle. In Worm threads the lead angle is as defined above, and in gears the helix angle is the

angle made by the pitch helix with the AXIS.

8. Best Size Wires: Wires which touch the thread at the pitch diameter are known as "Best Size"

Wires. Such wires are used because the measurements of pitch diameter are least affected by

errors that maybe present in the angle of the thread. The diameter of the measuring wires is

represented by the letter G.

Procedure:

Two Wire Method:

The effective diameter of a screw thread may be ascertained by placing two wires or rods of

identical diameter between the flanks of the thread, and measuring the distance over the outside

of these wires. The effective diameter is then calculated as

E=T+P

Where T= Dimension under the wires

=M—2d

M=dimension over the wires, d= diameter of each wire

13


The wires used are made of hardened steel to sustain the wear and tear in use. Theseare given a

high degree of accuracy and finish by lapping to suit different pitches.Dimension T can also be

determined by placing wires over a standard cylinder of diameter greater than the diameter under

the wires and noting the reading R1 and then taking reading with over the gauge, say R2.

Then T=S—(R1—R2).

P=It is a value which depends upon the diameter of wire and pitch of the thread.

If P= pitch of the thread, then

P= 0.9605p−1.1657d (for Whitworth thread).

P= 0.866p—d (for metric thread).

To give the effective diameter. The expression for the value of P in terms of p (pitch), d

(diameter of wire) and x (thread angle) can be derived as follows:

In Fig. since BC lies on the effective diameter line BC= ½ pitch=½ p

OP= (d cosec x/2)∕2

PA=d (cosecx∕2−1) ∕2

PQ=QC cot x∕2=p∕4 cot x∕2

AQ=PQ−AP= (p cot x∕2)∕4 – d (cosec x∕2 −1)∕2

AQ is half the value of P

.’. P value=2AQ =p∕2 cot x∕2 −d (cosecx∕2−1)

Two wire method can be carried out only on the diameter measuring machine described for

measuring the minor diameter, because alignment is not possible by two wires and can be

provided only by the floating carriage machine. In the case of three wire method, two wire, on

one side help in aligning the micrometer square to the thread while the third placed on the other

side permits taking of readings.

Three Wire Method:

This method of measuring the effective diameter is an accurate method. In this three wires or

rods of known diameter are used; one on one side and two on the other side [Fig. (a) and (b)].

This method ensures the alignment of micrometer anvil faces parallel to the thread axis. The

wires may be either held in hand or hung from a stand so as to ensure freedom to the wires to

adjust themselves under micrometer pressure.

M=distance over wires E=effective diameter r=radius of the wires d=diameter of wires h =height

of the centre or the wire or rod from the effective x=angle of thread.

14


fig. (a) fig. (b)

From fig.(b), AD = AB cosec x∕2 = r cosec x∕2

H = DE cot x∕2 = p∕2 cot x∕2

CD = ½H = p∕4 cot x∕2

H = AD−CD

r = cosec x∕2− p∕4 cot x∕2

Distance over wires=M = E+2h+2r = E+2(r cosec x∕2 – p∕4 cot x∕2)+2r = E+2r (l+cosecx∕2 )− p∕2

cot x∕2 or M = E+d (1+cosec x∕2) − p∕2 cot x∕2 (since 2r = 0 )

i)In case of Whitworth thread:

X = 55°, depth of thread = 0.64 p, so that

E= D—0.64 p and cosec x∕2 = 2.1657

Cot x∕2 = 1.921

M = E+d(1+cosec x∕2) — p∕2 cot x∕2 = D−0.64p+d(1+2.1657)−p∕2(1.921) = D+3.1657d−1.6005p

M = D+3.1657d—1.6p

Where D=outside dia

(ii) In case of metric threads:

Depth of thread=0.6495p

So, E = D-0.6495p.

x = 60°, cosec x∕2 = 2; cot x∕2 = 1.732

M = D−0.6495 p+d (l+2)—p∕2 (1.732)

= D+3d− (0.6495+0.866) p

= D+3d—1.5155p.

Result: The effective diameter of the given thread specimen =

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