Metrology (1).pptx

Engineering Metrology
Prof. Jeevan J Salunke
Mechanical Engineering Department
Deogiri Institute Of Engineering and
Management Studies, Aurangabad (M.S)

Program Outcomes (Pos)
• Graduate Attributes
• The Graduate Attributes are the knowledge skills and attitudes
which the students have at the time of graduation. These Graduate
Attributes identified by National Board of Accreditation (NBA) are
as follows:
• 1. Engineering knowledge: Apply the knowledge of mathematics,
science, engineering fundamentals and an engineering
specialization to the solution of complex engineering problems.
• 2. Problem analysis: Identify, formulate, research literature, and
analyze complex engineering problems reaching substantiated
conclusions using first principles of mathematics, natural sciences
and engineering sciences.

• 3. Design/development of solutions: Design solutions
for complex engineering problems and design system
components or processes that meet the specified
needs with appropriate consideration for the public
health and safety, and the cultural, societal, and
environmental considerations.
• 4. Conduct investigations of complex problems: Use
research-based knowledge and research methods
including design of experiments, analysis and
interpretation of data, and synthesis of the information
to provide valid conclusions.

• 5. Modern tool usage: Create, select, and apply
appropriate techniques, resources, and modern
engineering and IT tools including prediction and
modeling to complex engineering activities with
an understanding of the limitations.
• 6. The engineer and society: Apply reasoning
informed by the contextual knowledge to assess
societal, health, safety, legal and cultural issues
and the consequent responsibilities relevant to
the professional engineering practice.

Program Outcomes (POs)
• 7. Environment and sustainability:
Understand the impact of the professional
engineering solutions in societal and
environmental contexts, and demonstrate the
knowledge of, and need for sustainable
development.
• 8. Ethics: Apply ethical principles and commit
to professional ethics and responsibilities and
norms of the engineering practice.

• 9. Individual and team work: Function effectively
as an individual, and as a member or leader in
diverse teams, and in multidisciplinary settings.
• 10. Communication: Communicate effectively on
complex engineering activities with the
engineering community and with society at large,
such as, being able to comprehend and write
effective reports and design documentation,
make effective presentations, and give and
receive clear instructions.

• 11. Project management and finance:
Demonstrate knowledge and understanding of
the engineering and management principles and
apply these to one’s own work, as a member and
leader in a team, to manage projects and in
multidisciplinary environments.
• 12. Life-long learning: Recognize the need for,
and have the preparation and ability to engage in
independent and life-long learning in the
broadest context of technological change.

Metrology
• Definition: It is the science of measurements. It is
also about the correctness and accuracy of the
measurement.
• Metrology is mainly concerned with-
• 1. establishing the units of measurements,
introducing these units in the form of standards
and ensuring the uniformity of measurements.
• 2. developing methods of measurements
• 3. analyzing the accuracy of methods of
measurements

Metrology
4. researching into the causes of measuring
errors and eliminating these.
• It is also concerned with industrial inspection,
design, manufacturing and testing of gauges
of all kinds.

Legal Metrology
• Legal metrology is that part of metrology
which treats units of measurements, methods
of measurements and the measuring
instruments in relation to the statutory,
technical and legal requirements.
• It assures security and appropriate accuracy of
measurements.

Legal Metrology
• Legal metrology is directed by a national
organization, viz. National Service of Legal
Metrology whose object is to resolve problems of
legal metrology In a particular country.
• Its functions are to ensure the conservation of
national standards and to guarantee their
accuracy by comparison with international
standards; and also to impart proper accuracy to
the secondary standards of the country by
comparison with international standards.

Legal Metrology
• The activities of the service of Legal Metrology
are:
• 1. control (testing, verification,
standardization) of measuring instruments.
• 2. testing of prototypes/models/ of measuring
instruments
• 3. examination of measuring instruments to
verify its conformity to the statutory
requirements, etc.

Legal Metrology
• Legal metrology has application in:
• i) Commercial transactions (Ex: Grocery shops,
Petrol pumps, Cloth shops, Weigh bridges)
• ii) Industrial measurements (Ex: Vernier
caliper, Micrometer, vernier height gauge, All
types of measuring instruments and gauges.)
• iii) Measurements needed for ensuring public
health and human safety

Deterministic Metrology
• This is a new philosophy in which part
measurement is replaced by process
measurement. In deterministic metrology, full
advantage is taken of the deterministic nature
of production machines ( machines under
automatic control are totally deterministic in
performance) and all of the manufacturing
sub systems are optimized to maintain
deterministic performance within acceptable
quality levels.

Deterministic Metrology
• In this science, the system processes are
monitored by temperature, pressure, flow
force, vibration, acoustic “finger printing”
sensors, these sensors being fast and non-
intrusive. The new techniques such as 3D
error compensation by CNC systems and
expert systems are applied, leading to fully
adaptive control.

Standardization
• For overall higher economy, efficiency and
productivity in a factory and country, it is
essential that diversity be minimized and
interchangeability among parts encouraged.
All this is possible with standardization.
Standardization is done at various levels. Viz.
International, National, Association, Company.

Standardizing Organizations
• Realizing the role of standardization in the
development of industry, organizations to handle
the complexities of standardization have been
evolved in each of the chief industrial countries.
• In India, Bureau Of Indian Standards (BIS) is
responsible for evolving standards on
metrological instruments etc. There are several
sectional committees, each dealing with various
main branches of industry, in BIS.

• The detailed work of drawing up specifications
is done by more specialized technical
committees who prepare a draft based on
practice in other countries and the needs of
the country.
• This draft is circulated to relevant industries,
government and service departments,
research and teaching organizations.

• Comments are invited both from producer and
user to consider all aspects; meetings held to
discuss the matters in depth and final standards
issued. The technical committees also keep on
revising the existing standards from time to time.
• For engineering matters, the foremost standards
organization at international level is International
Organization for Standardization (ISO). The
national standards organization of individual
countries are the members of I.S.O.

• The I.S.O recommendations are used as basis for
national and company standards.
• National Physics Laboratory (NPL) provides the
basic backbone of organizational structure for
metrology in India. NPL is the custodian of
national measurement standards for physical
measurement in the country. NPL has the
responsibility of physical measurements based on
the International System (SI units) under the
subordinate legislation of Weights and Measures
Act 1956.

• NPL also has the statutory obligation to
establish, maintain and update the national
standards of measurement and calibration
facilities for different parameters. NPL
maintains seven SI base units ,viz., meter,
kilogram, second, kelvin, ampere, candela,
mole (mol) and the SI supplementary units
radian (rad) and steradians (sr).

• Following are the various standardizing
organizations-
• 1. International Organization of Weights and
Measures.
• 2. General Conference Of Weights & Measures
• 3. International Committee of Weights and
Measures.
• 4. International Organization Of Legal
Metrology

International System Of Units (SI)
• It is the system established in 1960 and
abbreviated as SI (System International) in all
languages. This SI, like traditional metric system is
based on decimal arithmetic.
• For each physical quantity, units of different sizes
are formed by multiplying or dividing a single
base value by powers of 10. Obviously this offers
great advantage because the changes can be
made very simply by adding zeros or shifting
decimal point.

• This system is superior to other systems and
also more convenient as it is coherent,
rational and comprehensive.
• The SI system is a coherent system, in the
sense that the product or quotient of any two
unit quantities in the system is the unit of the
resultant quantity.
• It is rational system since it has absorbed in
itself the rationalized MKSA system.

• It is also comprehensive because its base units
cover all disciplines.
• The seven base SI units established by the
General Conference Of weights and Measures
are given under-

Base SI Units
Sr.
No.
Physical Quantity Name of unit Unit Symbol Base of definition
1. Length Metre M Wavelength of red light
in Krypton 86
2. Time Second S Cycles of radiation of
cesium
3 Mass Kilogram Kg. Platinum cylinder
prototype
4 Temperature Kelvin K Absolute zero and
water
5 Electric Current Ampere A Force between two
conducting wires.
6 Luminous Intensity Candela Cd Intensity of an area of
platinum
7 Quantity of
substance
Mole Mol Amount of atoms in
Carbon 12

Sr.
No.
Physical Quantity Name of Unit Unit Symbol
1. Force Newton N=Kg-m/s
2. Work, Energy, Joule J= n-m
3. Power Watt W= J/s
4. Electric Charge Coulomb C= A.s
5. Electric Potential Volt V= W/A
6. Electric Capacitance Farad F= C/v
7. Electric Resistance Ohm Ω = V/A
8. Magnetic Flux Weber Wb = V.S
9. Magnetic Flux
Density
Tesla T = Wb/m
10. Inductance Henry H = V.S/ A
11. Luminous Flux Lumen Lm = c.d.sr
12. Illumination Lux Lx = lm/m
13. Frequency Hertz Hz= Cycles
14. Pressure Pascal Pa= N/m
15. Elect. Conductance Siemen S = A/V

Measuring Means
• The means of measurements could be classified
as follows-
• A) Standards: (Reference masters or setting
standards) These are used to reproduce one or
several definite values of a given quantity.
• B) Fixed Gauges: These are used to check the
dimensions, form position of product features.
• C) Measuring Instruments: These are used to
determine the values of the measured quantity.

Physical Measurement
• It is the act of deriving quantitative
information about a physical object or action
by comparison with a reference.
• It will be noted from this definition that there
are three important elements of a
measurement viz.
• 1. Measurand: i.e the physical quantity or
property like length, angle, temperature,
pressure etc. being measured.

Physical Measurement
• 2. Comparison or Comparator i.e the means
of comparing mesurand with some reference
to render a judgment.
• 3. Reference i.e the physical quantity or
property to which quantitative comparisons
are made.

Methods Of Measurement
• Any method of measurement should be
defined in such a detail and followed by such a
standard practice that there is little scope for
uncertainty. The nature of the procedure in
some of the most common measurements is
described below. Actual measurements may
employ one or more combinations of the
following-

• 1. Direct method: In this method, the value of a
quantity is obtained directly by comparing the
unknown with the standard. It involves no
mathematical calculations to arrive at the result. Ex:
Length measurement by means of a graduated scale.
• 2. Indirect method: In this method, several
parameters (to which the quantity to measured is
linked with) are measured directly and then the
value is determined by mathematical relationship.
Ex: Measurement of speed on the basis of distance
and time.

• 3. Fundamental or Absolute method: It is
based on the measurement of the base
quantities used to define the quantity. Ex:
Measurement of pressure with the aid of U-
tube manometer.
• 4. Comparison method: This method involves
comparison with either a known value of the
same quantity or another quantity which is
function of the quantity to be measured.

• Ex: Measurement of pressure by Bourdon tube
gauge.
• 5. Substitution method: In this method the
quantity to be measured is measured by direct
comparison on an indicating device by replacing
the measuring quantity with some other known
quantity which produces same effect on the
indicating device. Ex: Determination of
temperature with a Beckmann thermometer.

• 6. Transposition method: This is method of
measurement by direct comparison in which
the value of the quantity to be measured is
first balanced by an initial known value A of
the same quantity, next the value of the
quantity to be measured is put in the place of
that known value and is balanced again by a
second known value B.

• When balance indicating device gives the same
indication in both cases, the value of the quantity
to be measured is √AB. Ex: Determination of
mass by means of a balance and known weights.
• 7. Differential method: This method involves
measuring the difference between the given
quantity and a known master of near about the
same value. Ex: Determination of length by a
comparator.

• 8. Coincidence method: In this differential
method of measurement the very small
difference between the given quantity and the
reference is determined by the observation of the
coincidence of scale marks. Ex: Measurement of
length by Vernier caliper.
• 9. Null method: In this method the quantity to be
measured is compared with a known source and
the difference between these two is made zero.

• Ex: Measurement of an electrical resistance by
means of Wheatstone bridge and null indicator.
• 10. Interpolation method: In this method, the
given quantity is compared with two or more
known values of near about same value ensuring
at least one smaller and one bigger than the
quantity to be measured and the reading
interpolated. Ex: Linear interpolations between
scale marks on a scale.

• 11. Deflection method: In this method the
value of the quantity is directly indicated by
deflection of a pointer on a calibrated scale.
• Ex: Measurement of mass by spring balance.
• 12. Extrapolation method: In this method the
given quantity is compared with two or more
known values and extrapolating the values.

• 13. Complementary method: This is the
method of measurement by comparison in
which the value of the quantity to be
measured is combined with a known value of
the same quantity so adjusted that the sum of
these two values is equal to predetermined
comparison value. Ex: Determination of
volume of a solid by liquid displacement.

• 14. Composite method: It involves the
comparison of the actual contour of a
component to be checked with its contours in
maximum and minimum tolerable limits. This
method provide for the checking of the
cumulative errors of the interconnected
elements of the component which are
controlled through a combined tolerance.

• 15. Element method: In this method, the several
related dimensions are gauged individually i.e
each component element is checked separately.
• 16. Contact and Contactless method: In contact
method, the measuring tip of the instrument
actually touches the surface to be measured.
• In contactless method, no contact is required. Ex:
toolmaker’s microscope and projection
comparator.

Errors
• ERROR: Error is the difference between the mean
of set of readings on same component and the
true value. Less is the error more accurate is the
instrument.
• Sources of error: Measurement error is the
difference between the indicated and actual
values of the measurement.
• The error could be expressed either as an
absolute error or on a relative scale, most
commonly as a percentage of full scale.

Sources of Errors
• Each component of the measuring system has
sources of errors that can contribute to
measurement error.
• Instrument or indication errors may be caused
by defects in manufacture of adjustment of an
instrument, imperfection in design etc. The
error of measurement is the combined effect
of component errors due to various causes.

Sources of Errors
• There may be errors due to method of
location, environmental errors, errors due to
the properties of object of measurement, viz.
form deviation, surface roughness, rigidity,
change in size due to ageing etc., observation
errors.

Static Errors
• STATIC ERRORS: These result from the physical
nature of the various components of the
measuring system as that system responds to
a fixed measurand input. Static errors result
from the intrinsic imperfections or limitations
in the hardware and apparatus compared to
ideal instruments.

Static Errors
• a) Reading Errors: Reading errors describe
such factors as parallax, interpolation, optical
resolution, (readability or output resolution).
Reading errors apply exclusively to the
readout device.
• b) Environmental Errors: Environmental errors
result from effect of surrounding temperature,
pressure and humidity on measuring system.

Static Errors
• External influences like magnetic or electric fields,
nuclear radiation, vibration or shock, periodic or
random motion etc. also lead to errors.
• C) Characteristic Error: It is defined as the
deviation of the output of the measuring system
under constant environmental conditions from
the theoretically predicted performance or from
nominal performance specifications.

Loading Errors
• Loading errors: Loading errors result from the
change in the measurand itself when it is
being measured, i.e the measuring system or
instrument is connected for measurement.
Instrument loading error is thus the difference
between the value of the measurand before
and after the measurement.
• Ex: the deformation of soft component under
contact pressure of measuring instrument.

Dynamic Errors
• Dynamic Errors: Dynamic error is caused by
time variations in the measurand and results
from the inability of a measuring system to
respond faithfully to a time varying
measurand. Usually the dynamic response is
limited by inertia, damping, friction or other
physical constraints in the sensing or readout
or display system.

Systematic Errors
• Systematic or Controllable Errors: Systematic
errors are experimental mistakes. These are
controllable in both their magnitude and
sense. These can be determined and reduced,
if attempts are made to analyze them.
However they cannot be revealed by repeated
observations.

Systematic Errors
• These errors either have a constant value or a
value changing according to a definite law.
These can be due to-
• 1. Calibration Errors: The actual length of
standards such as slip gauges and engraved
scales will vary from nominal values by small
amount. Sometimes the instruments inertia,
hysterisis effect do not let the instrument
translate with complete fidelity.

Systematic Errors
• Often signal transmission errors such as drop in
voltage along the wires between the transducer and
the electric meter occur. For high order accuracy
these variations have positive significance and to
minimize such variations calibration curves must be
used.
• 2. Ambient Conditions: Variations in the ambient
conditions from international agreed standard value
of 20° C, barometric pressure 760 mm of mercury
and 10 mm of mercury vapor pressure, can give rise
to errors in the measured size of the component.

Systematic Errors
• 3. Stylus Pressure: Error induced due to stylus
pressure is also appreciable. Whenever any
component is measured under a definite
stylus pressure both the deformation of the
work piece surface and deflection of the work
piece shape will occur.
• 4. Avoidable Errors: These errors include the
errors due to the parallax and the effect of
misalignment of the work piece center.

Systematic Errors
• Instrument location errors such as placing a
thermometer in sunlight when attempting to
measure air temperature also belong to this
category.
• 5. Experimental arrangement being different
from that assumed in theory.
• 6. Incorrect theory i.e the presence of effects
not taken into account.

Static Characteristics
• Sensitivity : It is the quotient of the increase
in observed variable (indicated by pointer and
scale) and the corresponding increase in the
measured quantity.
• Sensitivity refers to minimum change in value
that the instrument can reliably indicate.
• Sensitivity refers to the ability of a measuring
device to detect small differences in a quantity
being measured.

• More the sensitive an instrument is, more
susceptible it will be to extraneous influences,
particularly vibration.
• Accuracy: Accuracy is the agreement of the result
of a measurement with the true value of the
measured quantity.
• Precision: It is defined as the repeatability of a
measuring process. Precision is concerned with a
process or a set of measurements and not a
single measurement.

• Precision tells us how well the various
measurements performed by same
instrument on the same component agree
with each other.
• Magnification: The human limitations or
incapability to read instruments places limit
on sensitiveness of instruments.
• Magnification (amplification) of the signal
from measuring instrument can make it better.

• The magnification is possible on mechanical,
pneumatic, optical, electrical, electronic
principles or combinations of these.
• Repeatability: It is defined as the ability of a
measuring system to reproduce output
readings when the same measured value is
applied to it consecutively under the same
conditions, and in same direction.

Repeatability and Reproducibility

• Reproducibility: The amount of variation in a
measurement system assigned to differences
in employees, measurement tools and
equipment, techniques, setup or other
physical factors.

• Readability: Readability refers to the
susceptibility of a measuring device to having
its indications converted to a meaningful
number.

Standards Of Measurements
• Two standard systems for linear measurement
used throughout the world are-
• English (Yard)
• Metric (Metre)
• Various standards for linear measurement are-
• I) Line Standard: According to this standard, yard
or metre is defined as the distance between
scribed lines on a bar of metal under certain
conditions of temperature and support.

• Yard: The imperial standard Yard is a bronze bar
of one inch square cross-section and 38 inches
long. A round recess, one inch away from two
ends is cut at both ends up to central plane of the
bar. A gold plug 1/10 ₺ diameter having three
lines engraved transversely and two lines
longitudinally is inserted into these holes so that
the lines are in neutral plane.
• Yard is then defined as the distance between the
two central transverse lines of the plug at 62⁰ F
(16.67⁰ C )

• Metre: This is the distance between the
centre portions of two lines engraved on the
polished surface of a bar of platinum-iridium
alloy (90% platinum and 10% iridium).
• It is inoxidizable and can have good polish
required for ruling good quality of lines. The
bar is kept at 0⁰C and under normal
atmospheric pressure.

Standards Of Measurement
• It is supported by two rollers of at least 1 cm
diameter symmetrically situated in the same
horizontal plane at a distance of 751 mm, so
as to give minimum deflection.
• Metre: It has a shape of winged section having
a web whose surface lines are on the neutral
axis. The section chosen gives maximum
rigidity and economy of costly material.

• Also the neutral axis lies at the top of the web
and, therefore, whole of it can be graduated.
Overall width and depth are 16 mm each. This
reference is designated as International
Prototype Metre-M in 1899. This standard is
kept at BIPM (French: Bureau international des
poids et mesures, English: International Bureau
Of Weights and Measures) at Serves, Paris.

• Fig.

• End Standard: For all practical measurements
in workshop, we employ end standards e.g
slip gauges, gap gauges, end of micrometer
anvils etc. Thus the importance of end
standards (which are actually used in general
measurement applications) arose.
• Length bars and slip gauges were then made
which were equal in length to the legal line
standard.

• The only difficulty realized with end standard was
that of forming two accurately parallel surfaces at
the end of a bar and to heat treat the ends so
that they remained stable.
• End bars or Length bars: These are used for the
measurement of larger sizes of work. These
consist of carbon steel round bar about 20 mm in
diameter and made in sizes varying from 10 mm
to 1200 mm. These are hardened only at ends up
to 800 HV and supported at ‘Airy’ points so that
end surfaces are parallel to each other.

• For bars above 150 mm size, the airy points
are indicated by pairs of circumferential lines
inscribed around the bars.
• Such bars are used for standardizing the
normally used one inch bars in combination.
These are , therefore, generally not found in
majority of engineering works but in
standardizing laboratories etc.

Standards Of measurements
• Sub-division of Standards: The imperial standard
yard and metre defined earlier are just like the
master standards and can’t be used for ordinary
purposes. Thus depending upon the importance
of standard , standards are sub-divided into four
grades-
• 1) Primary Standards(Reference): It is one and
only one material standard preserved under most
careful conditions. These are used after 10 to 20
years solely for comparison with primary
standards.

• 2) Secondary Standards(Calibration): These are
close copies of primary standards as regards both
design, material and length. These are made, as
far as possible, exactly similar to primary
standards. These are used for comparison with
tertiary standards whenever desired.
• 3. Tertiary Standards (Inspection): Tertiary
standards are reference standards employed by
National Physics Laboratory (NPL).

• These are also made as true copy of secondary
standards and are kept as reference for
comparison with working standards.
• 4) Working Standards: These are similar in
design to 1,2 & 3 but being less in cost are
made of lower grade materials. These are of
general application in metrology laboratories.

Wavelength Standard
• According to this standard metre is defined as
1650763* Wavelength of the radiation
corresponding to the transition between the
level 2p₁₀- 5d₅ of the Krypton86 atom in
vacuum.

Measurement & Calibration System
• All measuring equipments and measuring
standards should have records in regard to-
• 1. the description and unique identification
• 2. the date on which each calibration is
performed.
• 3. the results of calibration
• 4. the planned calibration interval
• 5. the designated permissible limits of error.

Measurement & Calibration System
• 6. the reference to calibration procedures.
• 7. Statement of cumulative effect of
uncertainties on the data obtained in
calibration
• 8. details of any maintenance (servicing,
adjustment, repairs etc. ) or modifications that
could affect the calibration status
• 9. any limitations in use

Traceability
• This is the concept of establishing a valid
calibration of a measuring instrument or
measurement standard by step-by-step
comparison with better standards up to an
accepted or specified standard. In general, the
concept of traceability implies eventual
reference to an appropriate national or
international standard.

Calibration
• Calibration is a set of operations that
establish, under specified conditions, the
relationship between values of quantities
indicated by a measuring instrument or values
represented by a material measure and the
corresponding values realized by standards.

Slip Gauges
• Slip gauges are also called as Johannsen
gauges as Johannsen originated them. These
are rectangular blocks of steel having a cross
section of 30*10 mm.
• These are first hardened to resist wear and
carefully stabilized so that they are
independent of any subsequent variation in
size or shape.

Slip Gauges
• After being hardened, blocks are carefully
finished on the measuring faces to such a fine
degree of finish, flatness and accuracy that any
two faces when perfectly clean may be ‘wrung’
together.
• These are classified according to their guaranteed
accuracy:
• 1. AA for master slip gauges( Accuracy + 2
microns/mtr.) Flatness and parallelism- 75
microns

Slip Gauges
• 2. A for reference purpose (Accuracy + 4
microns/mtr.) Flatness and parallelism- 125
microns
• 3. B for working slip gauges (Accuracy + 8
microns/mtr.) Flatness and parallelism-250
microns.
• Basic forms of slip gauges: Rectangular,
square, with centre hole and square without
centre hole.

Slip Gauges
• Wringing: It is defined as the property of
measuring faces of a gauge block of adhering by
sliding or pressing the gauge against the
measuring faces of other gauge blocks or the
reference faces of datum surfaces, without the
use of any extraneous means.
• The adhesion is partly caused by molecular
attraction and partly by atmospheric pressure.
The gap between the two wrung flat pieces is
0.00635 microns

Slip Gauges
• Manufacturing of slip gauges: Following is the
sequence of operations for the manufacturing of
slip gauges-
• 1. Making the approximate size by preliminary
operations.
• 2. A special form of heat treatment to make the
blocks hard and wear resistant.
• 3. Stabilizing is generally carried out by heating in
sand and cooling the gauges in stages
successively after rough grinding ( The
temperatures are 40°, 70°, 130° and 200° C).

Slip Gauges
• 4. A final grinding process to reduce the blocks
to the approximate required dimension.
• 5. A final lapping operation to reduce the
blocks to exact size and impart a beautiful
finish to the surface (at 20° C and 50%
humidity).
• 6. Comparison of finished gauges with grand
master sets.

Slip Gauges
• Lapping: The method utilizes special type of
magnetic chuck on which eight similar steel
blanks are mounted and spot ground on each
face.
• A preliminary lapping operation is carried out
on this chuck, by which all the blanks become
parallel to about 0.0002 mm and within about
0.002 mm of size.

Slip Gauges
• Care and Use of slip gauges:
• 1. All the surfaces are protected against climatic
conditions by being covered with a high grade
lanotin preparation, or petroleum jelly.
• 2. The joint between the lid and the case is made
with fillet and groove, to prevent the ingress of
dust.
• 3. The slip gauges are kept in a suitable case in
which there is a separate compartment for each
gauge.

Slip Gauges
• 4. The gauges should be used only in air
conditioned rooms free from dust and
maintained at constant temperature.
• 5. Care should be taken to protect the gauges
from getting magnetized, otherwise they will
attract metallic dust.
• 6. When the gauges are not in use they should
be kept only in their case which should be
kept closed.

Slip Gauges
• 7. Gauge blocks should be handled using a
piece of chamois leather or perspex tongs.
• 8. In case of new gauges, first the protective
coating applied to it should be removed with
petrol and finally gauges be wiped with a
clean soft linen cloth. The wiping should be
preferably be done every time before using
the gauges.

Slip Gauges
• 9. The handling should be as minimum as possible to
avoid transfer of heat from body to the gauge .
Handling would also corrode high finish of gauges due
to the natural acid in the skin.
• 10. If handling is unavoidable, the hands should be
washed and then coated with a film of pure petroleum
jelly.
• 11. Actually both the work to be tested and the gauges
wrung together should be allowed to settle down to
the prevailing temperature of the room before doing
any test.

Limits Fits and Gauges
• Tolerance: It can be defined as the magnitude of
permissible variation (deviation) of a dimension
or other measured or control criterion from the
specified value.
• The primary purpose of tolerances is to permit
variation in dimensions without degradation of
the performance beyond the limits established by
the specification of the design.
• The tolerance is compromise between accuracy
required for proper functioning and the ability to
economically produce this accuracy.

Limits, Fits and Gauges
• Functional Dimensions are those which have
to be machined and fit with other mating
components.
• Non-functional Dimensions are those which
need not be machined to high degree of
accuracy. They have no effect on the quality
performance of the component or assembly.

• Tolerances are specified due to following
reasons-
• 1. Variations in the properties of the material
being machined introduce errors.
• 2. The production machines themselves have
some inherent inaccuracies built into them
and have the limitations to produce perfect
parts.

• 3. It is impossible for an operator to make
perfect settings. In setting up the machine i.e
in adjusting the tools and work piece on the
machine some errors are likely to creep in.

• Different ways of expressing tolerances:
• Unilateral: In unilateral tolerances, the total
tolerance as related to a basic dimension is in
one direction only. This system is used in
drilling.
• Bilateral: In case of bilateral tolerances, the
total tolerance is specified on both sides (plus
and minus) of the basic dimension.

• Specifying Tolerances for given assembly: The
type of assembly i.e fit between two mating
components is decided based on functional
requirements.
• Based on it, tolerances on shafts and holes are
decided using two approaches-
• I) Complete Interchangeability: In this approach,
no risk is taken about even a single non
conforming assembly. If the fit between a shaft
and hole is a clearance type, then in this
approach-

• Tolerance on shaft= Tolerance on hole= half the
maximum clearance – half the minimum clearance
• 2) Statistical approach: This approach bases the
permissible tolerances on the normal distribution
curve, considering that only 0.3% components would
lie beyond + 3σ limits.
• Hence this approach allows wider tolerances compared
to complete interchangeability approach. It permits
cheaper production methods but can be used when
components are produced in bulk.

• Tolerance Accumulation: If a part comprises
of several steps, each step having some
tolerance over its length, then overall
tolerance on complete length will be sum of
the tolerances on individual length.

• Compound Tolerances: Compound tolerances
are those which are derived by considering
the effect of tolerances on more than one
dimension.

• Interchangeability: An interchangeable part is
one which can be substituted for similar part
manufactured to the same drawing.
• Any one component selected at random should
assemble correctly with any other mating
component, that too selected at random.
• When a system of this kind is ensured it is known
as interchangeability. Interchangeability ensures
increased output with reduced production cost.

• The required fit in an assembly can be
obtained in two ways-
• 1) Universal or Full Interchangeability: Full
interchangeability means that any component
will match with any other mating component
without classifying manufactured components
in sub group or without carrying out any
minor alterations for mating purposes.

• 2) Selective Assembly: In selective assembly
the components produced by a machine are
classified into several groups according to size.
This is done for both hole and shaft and then
the corresponding groups will match properly.
Ex: Piston and cylinder of I.C engine.

• Limits of size: There are three considerations
in deciding the limits necessary for a particular
dimension-
• a) functional requirement (function of the
component, what it is required to do)
• b) interchangeability (ease of replacement in
the event of failure)
• c) economics (minimization of production
time and cost)

• Indian Standard ( IS 919-1963): We follow this
standard for system of limits and fits.
• The system comprises suitable combination of
18 grades of fundamental tolerances (IT01, IT0
IT1,IT2, IT3,IT4, IT5, IT6, IT7,IT8, IT9, IT10,
IT11, IT12, IT13, IT14, IT15, IT16) and

Limit, Fits and Gauges
• 28 types of fundamental deviations indicated
by letter symbols for both holes and shafts.
• ( A to ZC for holes and a to zc for shafts) in
diameter steps up to 500 mm.
• For Holes: A,B,C,CD,D,E,EF,F,FG,G,H,JS, J,
K,M,N, P, R, S,T,U,V,X,Y,Z,ZA,ZB, and ZC
• For Shafts: a, b, c, cd, d, e,ef, f, fg, g, h, js, j, k,
m, n, p, r, s, t, u, v, x, y, z, za, zb, and zc

• HOLE: A term used by convention to designate
all internal features of a part including those
which are not cylindrical.
• SHAFT: A term used by convention to
designate all external features of a part
including those which are not cylindrical.

• Basic Size: It is the size of a part in relation to
which all limits of variations are determined.
• Zero Line: This is a line which represents the
basic size so that the deviation from the basic
size is zero.
• Actual Size: This is the measured size.
• Limits: These are two extreme permissible
sizes for any dimension (high and low).

• Allowances: An intentional difference
between the hole dimension and shaft
dimension for any type of fit is called the
allowance.
• Thus allowance is positive for clearance fit and
negative for interference fit.

Clearance Fit
• Fit: When two parts are to be assembled, the
relation resulting from the difference between
their sizes before assembly is called fit.
• 1. Clearance Fit: In this type of fit, the largest
permitted shaft diameter is smaller than the
diameter of the smallest hole, so that the
shaft can rotate or slide through with different
degrees of freedom according to the purpose
of the mating members.

Interference Fit
• 2. Interference Fit: In this type of fit, the
minimum permitted diameter of the shaft is
larger than the maximum allowable diameter
of the hole. In this case, the shaft and the hole
members are intended to attached
permanently and used as a solid component.

Transition Fit
• 3. Transition Fit: In a fit of this type the
diameter of the largest allowable hole is
greater than that of the smallest shaft, but the
smallest hole is smaller than the largest shaft,
so that small positive or negative clearance
between the shaft and hole members are
employable.
• Ex: Spigot in mating holes, coupling rings and
recesses.

• Minimum Clearance: In a clearance fit, it
refers to the difference between the minimum
size of hole and the maximum size of shaft.
• Maximum Clearance: In the case of clearance
or transition fit, it refers to the difference
between the maximum size of hole and the
minimum size of shaft.

• Minimum Interference: It is the difference
between the maximum size of hole and the
minimum size of shaft in an interference fit
prior to assembly.
• Maximum Interference: In an interference fit
or a transition fit it is the difference between
the minimum size of hole and the maximum
size of shaft prior to assembly.

• Deviation: It is defined as the algebraic
difference between a size (actual, maximum
etc.) and the corresponding basic size.
• Upper Deviation: It is the algebraic difference
between maximum limit of size (of either hole
or shaft) and the corresponding basic size. It is
designated by letters ‘ES’ for hole and ‘es’ for
shaft.

• Lower Deviation: It is algebraic difference
between minimum limit of size (of either hole
or shaft) and the corresponding basic size. It is
designated by ‘EI’ for a hole and ‘ei’ for a
shaft.

• Fundamental Deviation: It is that one of the
two deviations which is conventionally chosen
to define the position of the tolerance zone in
relation to the zero line. This may be upper or
lower deviation which is closest to the zero
line. It fixes the position of zero line.

• Basic Hole: It is a hole whose fundamental
deviation (lower deviation) is zero or whose
minimum limit of size is equal to its basic size.
Ex: Hole ‘H’ in IS 919: 1963
• Basic Shaft: It is a shaft whose fundamental
deviation (upper deviation) is zero or whose
maximum limit of size is equal to its basic size.
Ex: Shaft ‘h’ in IS 919:1963

• For Shafts ‘a’ to ‘h’ the deviation is below the
zero line and for shafts ‘j’ to ‘zc’ it is above the
zero line.
• For Holes ‘A’ to ‘G’ lower deviation is above
the zero line and for ‘J’ to ‘ZC’ it is below the
zero line.

Sr.
No.
For Shaft For Hole
1. Lower Deviation ei= es-IT EI= ES-IT
2. Upper Deviation es= ei+IT ES= EI + IT
Where IT is the
grade of Tolerance

Tolerance Grades
• IT 01 = 0.3 + 0.008 microns
• IT 0 = 0.5 + 0.012 microns
• IT 1 = 0.8 + 0.020 microns
Where,
i=0.45* Cube root of D + 0.001 D microns
IT 5 IT 6 IT 7 IT 8 IT 9 IT 10 IT 11 IT 12 IT13 IT14 IT 15 IT 16
7i 10i 16i 25i 40i 64i 100i 160i 250i 400i 640i 1000i

Tolerance Grades
• The tolerance grade decides the accuracy of
manufacturing.
• The seven finest grades (IT01 TO IT5) cover
sizes up to 500 mm and the eleven coarsest
grades up to 3150 mm.

Tolerance Grade Class of work
IT 01, IT 0, IT 1 Gauge blocks
IT2 High quality gauges, Plug Gauges
IT3 Good quality gauges, gap gauges
IT4 Gauges precise fit produced by lapping
IT5 Ball bearings, Machine lapping, Fine boring and grinding
IT6 Grinding fine boring
IT7 High quality turning, broaching, boring
IT8 Centre lathe turning & boring, reaming
IT9 Capstan or automatic lathes, boring machine
IT10 Milling, Slotting, Planing, Rolling, Extrusion
IT11 Drilling, Rough turning and Boring
IT12 Light press work, Tube drawing
IT13 Press work, Tube rolling
IT14 Stamping
IT15 Sand Casting Flame cutting

Diameter Steps
• Where D= Diameter in mm.
• D= √D1*D2 where D1 and D2 are lower and
upper diameter (of the diameter step) in mm.
• The various diameter steps specified by IS 919
: 1963 are-
• 1-3, 3-6,6-10,10-14, 14-18, 18-24, 24-30, 30-
40, 40-50, 50-65, 65-80, 80-100, 100-120, 120-
140, 140-160, 160-180, 180-200, 200-250,
250-315, 315-400, and 400-500 mm.

Hole Basis System and
Shaft Basis System

Gauges
• Plain Guages: Gauges are inspection tools of
rigid design, without a scale, which serve to
check the dimensions of manufactured parts.
Gauges do not indicate the actual value of the
inspected dimension on the work. They can
only be used for determining as to whether
the inspected parts are made within the
specified limits.
• These are also called as Fixed Gauges.

Gauges
• Advantages of Plain /Fixed Gauges:
• 1. Fixed gauges are essentially free from errors
due to drift and the original adjustment.
• 2. These provide positive dimensional
information.
• 3. These are portable and independent of power
supply.
• 4. These involve no other auxiliary equipment
and set-up.

Gauges
• 5. These can be designed to check
combinations of several dimensions
comprising lengths, diameters and angles.
• 6. These can be designed to inspect
interrelated features for size, location, form,
alignment etc. so as to check the virtual size of
a member.
• 7. These provide uniform reference standards.
• 8. These are not expensive.

Gauges
• Taylor’s Principle: Taylor’s principle states
that-
• 1. the ‘GO’ gauge should check all the possible
elements of dimensions at a time (roundness,
size, location etc.) and should be able to
control the maximum metal limit/condition,
• 2. the ‘NO GO’ gauge should check only one
element at a time, for minimum metal
limit/condition.

Gauges
• The ‘GO’ plug gauge must be of corresponding
section and preferably full length of hole so
that straightness of hole can also be checked.
• The ‘NO GO’ plug gauge is relatively short and
its function is dependent not only on the
diameter but also on the circularity of the
hole.

Gauges
• Maximum Metal Limit/Condition: It
corresponds to condition when a part has
maximum amount of metal i.e corresponding to
high tolerance of shaft (maximum limit) and low
tolerance of hole.
• Minimum Metal Limit/Condition: It corresponds
to condition when a part has minimum amount
metal i.e corresponding to lower tolerance of
shaft (minimum limit) and higher tolerance of
hole( maximum limit).

Gauges
• Wear Allowance: The measuring surfaces of ‘GO’
gauges which constantly rub against the surfaces
of parts in inspection, are consequently subjected
to wear and lose their initial size.
• Thus due to wear, the size of ‘GO’ plug gauge is
reduced, while that of ‘GO’ snap gauge is
increased. Therefore a special allowance of
metal, the wear allowance is added in a direction
opposite to the wear.

Gauges
• For this reason new ‘GO’ plug gauges are
made with two positive deviations and ‘GO’
snap gauges with two negative deviations
from the nominal size.

Gauges
• System for giving tolerances on gauges: In this
system, following principles are followed along
with Taylor’s principle-
• I) Tolerance should be as wide as is consistent
with satisfactory functioning, economical
production and inspection.
• II) No work should be accepted which lies
outside the drawing specified limits.

Gauges
• In this system we give the same tolerance
limits on workshop and inspection gauges and
the same gauges can be used for both
purposes.
• The tolerance zone for the ‘GO’ gauges should
be placed inside the work limits and tolerance
zone for the ‘NO GO’ gauges out side the work
limits.

Gauges
• Provision for wear of ‘GO’ gauges is made by
introduction of a margin between the
tolerance zone for the gauge and the
maximum metal limit of the work. Wear
should not be permitted beyond the
maximum metal limit of the work, when the
limit is of critical importance.
• Wear allowance is 1/10 th of the gauge
tolerance.

Comparators
• A comparator works on relative
measurements i.e to say, it gives only
dimensional differences in relation to a basic
dimension.
• A comparator has to compare the unknown
dimensions of a part with some standard or
master setting which represents the basic size,
and dimensional variations from the master
setting have to be amplified.

Comparators
• Advantages:
• 1. Not much skill is required on the part of
operator in its use.
• 2. Calibration of instrument over full range is not
required as comparison is done with a standard
end length.
• 3. Zero error of instrument also does not lead to
any problem.
• 4. Since range of indication is very small, being
the deviation from set value, a high magnification
resulting into great accuracy is possible.

Comparators
• Characteristics:
• 1. The instrument must be of robust design and
construction so as to withstand the ordinary
usage.
• 2. Readings should be obtained in least possible
time. The system should be free from backlash
and wear effects and the inertia should be
minimum possible.
• 3. Provision must be made for maximum
compensation for temperature effects.

Comparators
• 4. The scale must be linear and must have straight line
characteristic.
• 5. Indicator should be constant in its return to zero.
• 6. Instrument must be sensitive, however it must
withstand a reasonable ill usage without permanent
harm.
• 7. Instrument must have the maximum versatility i.e its
design must be such that it can be used for a wide
range of operations.
• 8. Measuring pressure should be low and constant.

Comparators
• Uses:
• 1. In mass production, where components are to be
checked at a very fast rate.
• 2. As laboratory standards from which working or
inspection gauges are set and co-related.
• 3. For inspecting newly purchased gauges.
• 4. Attached with some machines, these can be used as
working gauges.
• 5. In selective assembly of parts, where parts are
graded in three or more groups depending upon their
tolerances.

Johansson Mikrokator
• The pointer at the centre of the twisted strip
rotates by an amount proportional to the change
in length of strip and hence proportional to the
plunger movement.
• In order to prevent excessive stress on the central
portion, the strip is perforated along the centre
line by perforations.
• It works on the principle of a button spinning on a
loop of string.
• Magnification is X 5000.

Johansson Mikrokator
• Amplification of the instrument is dθ/dl is
directly proportional to l/w²n.
• Where,
• θ- the twist of mid-point of strip w.r.t end
• l- the length of twisted strip measured along
its N.A
• w- width of twisted strip
• N- number of turns

Reed type Mechanical Comparator

Optical Comparator
• In this comparator small displacements of the
measuring plunger are amplified fist by a
mechanical system consisting of pivoted
levers.
• The amplified mechanical movement is
further amplified by a simple optical system
involving the projection of an image.
• Mechanical amplification= l₂/l₁
• Optical amplification= l₄/l₃ * 2

Optical Comparator
• Advantages:
• 1. High degree of measuring precision owing to
high magnification and the reduction of moving
members to minimum.
• 2. These possess better wear resistance qualities
as the only wearing members are the plunger and
its guide and the mirror pivot bearing.
• 3. It has an illuminated scale which enables
readings to be taken very easily.

Zeiss Ultra-Optimeter
• A lamp sends light rays to green filter which
filters all but green light, which is less fatiguing
to the eye. The green light then passes to a
condenser which via an index mark projects it
on to a movable mirror M₁, where it is
reflected to another fixed mirror M₂ and then
back again to the first movable mirror.

Zeiss Ultra-Optimeter
• The second objective lens brings the reflected
beam from the first mirror to a focus at a
transparent graticule containing a precise
scale which is viewed by the eye piece.

Eden-Rolt Millionth Comparator

Electronic Comparator
• The electronic gauging system is designed to
fulfill the increasing demand for equipment
particularly suited to the accuracy and
versatility required by up to date engineering
practice.

Electronic Comparator
• The movement at the probe tip actuates
inductance transducer which is supplied with
an alternating current from the oscillator.
• The transducer converts this movement into
an electrical signal which is then amplified and
fed via an oscillator to the demodulator. The
current in DC form then passes to the meter
and the probe tip movement is displayed as a
linear measurement.

Pneumatic Comparators
• Air gauging has rapidly increased during past time
due to the following important characteristics-
• 1. Very high amplifications are possible. It can be
used to measure diameter, length, squareness,
parallelism, concentricity, taper, center distance
between holes etc.
• 2. As no physical contact is made , there is no loss
of accuracy because of gauge wear. Also very soft
parts which are easily scratched, can be gauged.

• 3. Internal dimensions can be readily measured
not only w.r.t tolerance boundaries but also
geometric form. Ex: While measuring a bore it
can reveal complete story of size, taper,
straightness, camber and bell mouth etc.
• 4. It is independent of operator skill.
• 5. High pressure can be done with cleansing of
the parts which helps to eliminate errors due to
dirt and foreign matter.

• 6. Gauging pressures can be kept sufficiently
low to prevent part deflection.
• 7. Dimensional variations throughout the
length of shaft or cylinder bore can be
explored for out of roundness, taperness,
concentricity, regularity, and similar
conditions.
• 8. The total life cost of the gauging heads is
much less.

• 9. It is accurate, flexible, reliable, universal and
speedy device for inspecting parts in mass
production.
• 10. It is best suited for multiple dimensions
and conditions on a part simultaneously in
least possible time. It can be used for parts
from 0.5 mm to 900 mm diameter having
tolerance of 0.05 mm or less.

• It can be easily used for on line measurement
of parts as they are being machined and take
corrective actions.

Measurement by Light Wave
Interference

Moire Fringes
• Moire is the name given to the patterns formed
by the overlapping of two layers of fine fabrics.
• Moire fringes are observed when the index
grating, instead of being kept parallel to the scale
grating, is rotated slightly in its own plane.
• Under such condition, the lines of the two
gratings intersect and the intersections are clearly
visible as dark moire fringes running
approximately at right angles to the grating lines.

• If the index grating is moved transversely, then
the moire fringes move up or down and the
position of the fringes repeats itself every
time the grating has moved one grating
period.

Angular Measurement
• Sine Bar: The sine bar uses the sine principle.
The sine principle uses the ratio of the length
of two sides of a right angle triangle in
deriving a given angle.
• Features of Sine Bar:
• 1. The two rollers must have equal diameter
and be true cylinders.
• 2. The rollers must be set parallel to each
other and to the upper surface.

Sine Bar
• 3. The precise center distance between the rollers must
be known.
• 4. The upper face must be a high degree of flatness.
• Limitations of Sine Bar:
• 1.The sine bar is physically clumsy to hold in position.
• 2. The body of the sine bars cause large angular errors.
• 3. Slight error of the sine bar cause large angular error.
• 4. Long gauge stacks are not nearly as accurate as
shorter gauge blocks.

Sine Bar
• 5. Temperature variation becomes more critical.
• 6. The size of gauges, instruments or parts that a
sine bar can inspect is limited, since it is not
designed to support large or heavy objects.
• Precautions in use of Sine Bars:
• 1. The sine bar should not be used for angle
greater than 60° because any possible error is
construction is accentuated at this limit.

Sine Bar
• 2. A compound angle should not be formed by
misaligning of work piece with the sine bar.
This can be avoided by attaching the sine bar
and work against an angle plate.
• 3. Accuracy of sine bar should be ensured.
• 4. As far as possible longer sine bar should be
used since many errors are reduced by using
longer sine bars.

Sine Table
• This is the development of the sine bar. The
sine table is the most convenient and accurate
design for heavy work pieces.
• The table is quite rugged one and the weight
of unit and work piece is given fuller and safer
support. The gauging platforms are self
contained and can be highly refined. The table
may be safely swung to any angle from 0° to
90° by pivoting it about its hinged end.

Sine Centre
• Sine Centre is basically a sine bar with block
holding centers which can be adjusted and
rigidly clamped in any position. These are
used for inspection of conical objects (having
male and female centers) between centers.
These are used up to inclination of 60°.

Angle Gauges
• Angle Gauges: In the same way, as slip gauges
are built up to give a linear dimension, the
angle gauges can be build up to give a
required angle.
• Angle gauges are made up of hardened steel
and seasoned carefully to ensure permanence
of angular accuracy. The measuring faces are
lapped and polished to high degree of
accuracy and flatness like slip gauges.

Angle Gauges
• These gauges are about 3” (76.2 mm) long,
5/8” (15.87 mm) wide with their faces lapped
to within 0.0002 mm and angle between two
ends to + 2 seconds.
• There are total 13 gauges in a set-
• First series- 1°, 3°, 9°, 27°, 41°
• Second series- 1’,3’, 9’, 27’
• Third series- 3”, 6”, 18”, & 30”

Autocollimator
• Autocollimator: This is an optical instrument
used for the measurement of small angular
differences. It provides a very sensitive and
accurate approach.
• Autocollimator is essentially an infinity
telescope and a collimator combined into one
instrument.

Autocollimator
• Principle of autocollimator: A cross line “target”
graticule is positioned at the focal plane of a
telescope objective system with the intersection
of the cross line on the optical axis. i.e at the
principal focus.
• When the target graticule is illuminated, rays of
light diverging from the intersection point reach
the objective via a beam splitter and are
projected from the objective as parallel pencils of
light.

Autocollimator
• In this mode the optical system is operating as
a “Collimator”.
• A flat reflector placed in front of the objective
and exactly normal to the optical axis reflects
the parallel pencils of light back along their
original paths.
• They are then brought to focus in the plane of
the target graticule and exactly coincident
with its intersection.

Autocollimator
• A proportion of the returned light passes straight
through the beam splitter and the return image
of the target cross line is therefore visible through
the eye piece. In this mode the optical system is
operating as a telescope focused at infinity.
• If the reflector is tilted through a small angle the
reflected pencils of light will be deflected by
twice the angle of tilt and will be brought to focus
in the plane of the target graticule but linearly
displaced from the actual target cross lines by an
amount 2θxf.

Autocollimator
• Linear displacement of the graticule image in the
plane of the eye piece is therefore directly
proportional to the reflector tilt and can be
measured by an eye piece graticule, optical
micrometer or electronic detector system, scaled
directly in angular units.
• The autocollimator is set permanently at infinity
focus and no device for focusing adjustment for
distance is provided or desirable.

Autocollimator
• It responds only to reflector tilt (not lateral
displacement of the reflector). This is
independent of separation between the reflector
and the collimator, assuming no atmospheric
disturbance and the use of a perfectly flat
reflector.
• Many factors govern the specification of an
autocollimator, in particular its focal length and
its effective aperture. The focal length determines
basic sensitivity and angular measuring range.

Autocollimator
• The longer the focal length the longer is the
linear displacement for a given reflector tilt,
but the maximum reflector tilt which can be
accomodated is consequently reduced.

Angle Dekkor
• Angle Dekkor: This is also a type of an
autocollimator. It contains a small illuminated
scale in the focal plane of the objective lens
(collimating lens). This scale in normal position is
outside the view of the microscope eye piece.
• The illuminated scale is projected as a parallel
beam by the collimating lens which after striking
a reflector below the instrument is refocused by
the lens in the field of view of the eye piece.

Angle Dekkor
• In the field of view of microscope there is another
datum scale fixed across the centre of screen and
the reflected image of the illuminated scale is
received at right angle to this fixed scale and the
two scales, in this position intersect each other.
• Thus the reading on the illuminated scale
measures angular deviations from one axis at 90°
to the optical axis and the reading on the datum
scale measures the deviation about an axis
mutually perpendicular to the other two.

Angle Dekkor
• Uses of Angle Dekkor:
• 1. Measuring angle of a component
• 2. To obtain precise angular setting for
machining operations.
• 3. Checking the sloping angle of a V-block
• 4. To measure the angle of cone or taper
gauge.

Measurement Of Surface Finish
• Due to conditions not being ideal, the surface
produced during various manufacturing
processes, will have some irregularities which
could be classified into four categories-
• 1. First Order: This includes the irregularities
arising out of inaccuracies in the machine tool
itself e.g lack of straightness of guide ways on
which tool post is moving.

• 2. Second Order: Some irregularities are
caused due to vibrations of any kind such as
chatter marks and are included in this
category.
• 3. Third Order: Some irregularities are caused
by machining itself due to characteristics of
the process, which includes the feed marks of
the cutting tool.

• 4. Fourth Order : This includes the irregularities
arising from the rupture of the material during
the separation of the chip.
• First Group includes irregularities of considerable
wavelength of periodic characteristics resulting
from mechanical disturbances in the generating
set up. These errors are termed as macro-
geometrical errors and include irregularities of
first and second order.

• These errors are also referred to as Waviness or
Secondary texture.
• Second Group includes irregularities of small
wavelength caused by the direct action of the
cutting element on the material or by some other
disturbance such as friction, wear or corrosion.
• These errors are termed as micro-geometrical
errors and include irregularities of third and
fourth order. These errors are also referred to as
Roughness or Primary Texture.

• Thus any finished surface could be considered
to be combination of two forms of wavelength
(large wavelength for waviness and smaller
wavelength for roughness) superimposed
upon each other. One of the problems in
measuring surface finish is to separate the
waviness form the roughness.

• Primary Texture (Roughness): It is caused due to
the irregularities in the surface roughness which
result from the inherent action of the production
process. These are deemed to include transverse
feed marks and the irregularities within them.
• Secondary Texture (Waviness): It results from the
factors such as machine or work deflections,
vibrations, chatter, heat treatment or warping
strains.

• Waviness: It is the component of surface
roughness upon which roughness is
superimposed.
• Lay: It is the direction of the predominant
surface pattern, ordinarily determined by the
production method used. The surface
roughness is generally measured across the
direction of lay.

• Flaws: Flaws are irregularities which occur at one
place or at relatively infrequent or widely varying
intervals in a surface (like scratches, cracks etc. )
• Sampling Length (l): It is the length of profile
necessary for the evaluation of the irregularities
to be taken into account. For majority of
engineering work, value of 0.8 mm is generally
considered to be quite satisfactory and upper
limit of 25 mm is commonly accepted.

• Traversing Length: It is the length of the
profile necessary for the evaluation of the
surface roughness parameters. The traversing
length may include one or more sampling
lengths.

• Mean Line: It is the line having the form of the
geometrical profile and dividing the effective
profile so that within the sampling length the
sum of the squares of distances (y₁, y₂, y₃,……yn)
between effective points and mean line is a
minimum.
• Centre Line: It is the line parallel to the general
direction of the profile for which the areas
embraced by the profile above and below the line
are equal. When the waveform is repeatitive, the
mean line and the centre line are equivalent.

• Spacing of the irregularities: It is the mean
distance between the more prominent
irregularities of the effective profile, within
the sampling length.
• Arithmatic Average Roughness (Ra): It is
defined as the average value of the ordinates
(y₁,y₂,y₃…..yn) from the mean line. The
ordinates are summed up without considering
their algebraic sign.

• Average Peak to Valley height (Rz): This is the
average of single peak-to-valley heights from five
adjoining sampling lengths.
• Rt Measurement : It is the maximum peak to
valley height within the assessment length. This
measurement is valuable for analyzing finish to
provide guidance for planning subsequent metal
cutting operations.
• Bearing area: This is the fraction of surface at a
given height above or below the mean line.

• Depth of Surface Smoothness (Rp): It
indicates the amount of material to be
removed from a work piece to obtain 50%
bearing area.
• Leveling Depth (Ru): Distance between mean
line and a parallel line through highest peaks.
• Mean Depth (Rm): Distance between mean
line and a parallel line through the deepest
valley.

Sr.No. Roughness
grade no.
Roughness
value Ra (µm)
Roughness symbol
1. N12 50
2. N11 25
3. N10 12.5
4. N9 6.3
5. N8 3.2
6. N7 1.6
7. N6 0.8
8. N5 0.4
9. N4 0.2
10. N3 0.1
11. N2 0.05
12. N1 0.025

Sr.No Mfg. Process Ra value in
µm
1. Casting Sand casting 5 to 50
2. Permanent mould casting 0.8 to 6.3
3. Die casting 0.8 to 3.2
4. High pressure casting 0.32 to 2
5. Hot working Hot rolling 2.5 to 50
6. Forging 1.6 to 25
7. Extrusion 0.16 to 5
8. Flame cutting, Sawing & Chipping 6.3 to 100
9. Machining Radial cut off, sawing 1 to 6.3
10. Hand/Disc grinding 1.6 to 25
11. Filing 0.25 to 25
12. Planing 1.6 to 50

Sr.
no.
Mfg. Process Ra value in µm
13. Machining Shaping 1.6 to25
14. Drilling 1.6 to 20
15. Turning and Milling 0.32 to 25
16. Boring, Reaming, Broaching, Hobbing 0.4 to 3.2
17. Grinding and
Super finishing
Cylindrical/Surface grinding 0.063 to 5
18. Honing 0.025 to 0.4
19. Lapping 0.012 to 0.16
20. Polishing 0.04 to 0.16
21. Burnishing 0.04 to 0.8
22. Super finishing 0.16 to 0.32

Preferred Values
• Preferred values of Ra- Preferred values of Ra
are selected from 0.025, 0.05, 0.1, 0.2, 0.4,
0.8, 1.6, 3.2, 6.3, 12.5, and 25
• Preferred values of Rz- 0.05, 0.1, 0.2, 0.4, 0.8,
1.6, 3.2, 6.3, 12.5, 25, 50 and 100

• Stylus Probe Instruments: This type of
instruments generally consists of the following
units-
• 1. A Skid or Shoe which drawn slowly over the
surface either by hand or by motor drive. The
skid when moved over the surface, follows its
general contours and provides a datum for the
measurements.

• 2. A Stylus or Probe which moves over the
surface with the skid. The stylus for Ra
measurement on new instrument can have a
radius of 10 microns + 30%. When in use, tip
radius is allowed to vary + 50% ( 5to 10
microns). However for calibration purposes,
stylus should have 10 microns nominal size
radius + 20%.

• The stylus should have cone shaped with a
spherical tip. This records the micro
geometrical form of the surface. Generally it is
desired that if the skid is moving up then the
stylus must also be moving up.
• 3. An amplifying device for magnifying the
stylus movement and an indicator.
• 4. A recording device to produce a trace or
record of the surface profile.

• Usually the vertical movement is magnified
more in comparison to horizontal movement,
thus the record will not give the actual picture
of surface roughness but a distorted trace
obtained.
• 5. A means for analyzing the trace obtained.
The analysis can be done separately or some
automatic device may be incorporated in the
instrument for analysis.

Tomlinson Surface Meter
• The diamond stylus on the surface finish recorder
is held by spring pressure against the surface of a
lapped steel cylinder. The stylus is also attached
to the body of the instrument by a leaf spring and
its height is adjustable to enable the diamond to
be positioned conveniently.
• The lapped cylinder is supported on one side by
the stylus and on the other side by two fixed
rollers.

• The stylus is restrained from all motions except
the vertical one by tensions in coil and leaf spring.
The tensile forces in these two springs also keep
the lapped steel cylinder in position between the
stylus and a pair of fixed rollers.
• A light spring steel arm is attached to the
horizontal lapped steel cylinder and it carries at
its tip a diamond scriber which bears against a
smoked glass.

• When measuring surface finish, body is
traversed across the surface by a screw
rotated by a synchronous motor. Any vertical
movement of the stylus caused by the surface
irregularities, causes the horizontal lapped
steel cylinder to roll.
• By its rolling, the light arm attached to its end
provides a magnified movement on a smoked
glass plate.

• This vertical movement coupled with the
horizontal movement produces a trace on the
glass magnified in vertical direction and there
being no magnification in horizontal direction.
• The smoked glass trace is then, further
projected at x 50 or x100 magnification for
examination.
• This instrument is comparatively cheap one
and gives reliable results.

The Taylor Hobson Talysurf
• It is an electronic instrument working on carrier
modulating principle.
• The measuring head of this instrument consists of
a diamond stylus of about 0.002 mm tip radius
and skid or shoe which is drawn across the
surface by means of motorized drive unit
(gearbox), which provides three motorized
speeds giving respectively X20 and X100
horizontal magnification and a speed suitable for
average reading.

• The arm carrying the stylus forms an armature
which pivots about the center piece of an E-
shaped stamping. On two legs of (outer pole
pieces) the E-shaped stamping there are coils
carrying an A.C current.
• These two coils with other two resistances form
an oscillator. As the armature is provided about
the central leg, any movement of the stylus
causes the air gap to vary and thus the amplitude
of the original A.C current flowing in the coils is
modulated.

• The output of the bridge thus consists of
modulation only. This is further demodulated
so that the current now is directly
proportional to the vertical displacement of
the stylus only.
• The demodulated output is caused to operate
a pen recorder to produce a permanent record
and a meter to give a numerical assessment
directly.

• In recorder of this instrument the marking
medium is an electric discharge through a
specially treated paper which blackens at the
point of the stylus, so this has no distortion
due to drag and the record is strictly
rectilinear one.

Tracer type Profilogram
• The surface to be tested is placed on a working
table. The table can move to and fro by motion
given by motor. The stylus is made to rest on the
surface to be tested, is pivoted with mirror.
• When the surface to be tested moves, the
oscillations of the tracer are transmitted to the
mirror. The beam of light (received from light
source and through the lens and precision slit)
strikes on the oscillating mirror and is reflected

Tracer type Profilogram
• On to the revolving drum, upon which
sensitized film is arranged. The drum is also
rotated from the same lead screw that
traverses the table through bevel gears.
• The trace obtained is very much magnified
one and can be further assessed by various
methods.

Metrology (1).pptx

Recommended

Recommended

More Related Content

Similar to Metrology (1).pptx

Similar to Metrology (1).pptx (20)

Recently uploaded

Recently uploaded (20)

Metrology (1).pptx