Ch 1 introduction to metrology, linear and angular measurement

MECHANICAL MEASUREMENT & METROLOGY
(3141901)
CH-1: INTRODUCTION TO METROLOGY, LINEAR AND
ANGULAR MEASUREMENT
PREPARED BY:
PROF. SURAJ A. SHUKLA

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 a 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.

INTRODUCTION
• Thus, in 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.

NEED FOR INSPECTION
• Inspection means checking of all materials, products or component parts at various stages during
manufacturing. It is the act of comparing materials, products or components with some established standard.
• In the old days, the production was on small scale, different component parts were made and assembled by
the same craftsman. If the parts do not fit properly at the time of assembly, he used to make the necessary
adjustments in either of the mating parts so that each assembly functions properly.
• Therefore, it was not necessary to make similar parts exactly alike or with the same accuracy as there was no
need for accuracy.
• Due to technological development, new production techniques have been developed. The products are being
manufactured on a large scale due to low-cost methods of mass production.
• So, the hand-fit method cannot serve the purpose anymore. The modern industrial mass production system is
based on interchangeable manufacture when the articles are to be produced on a large scale.

NEED FOR INSPECTION
• In mass production, the production of a complete article is broken up into component parts. Thus, the
production of each component part becomes an independent process.
• The different component parts are made in large quantities in different shops. Some parts are purchased from
other factories also and then assembled together in one place.
• Therefore, it becomes essential that any part chosen at random should fit properly with any other mating parts
that too selected at random.
• This Is only possible when the dimension of the component parts are made with close dimensional tolerances.
This is only possible when the parts are inspected at various stages during manufacturing.
• When a large number of identical parts are manufactured on the basis of interchangeability if their
dimensions are actually measured every time a lot of time will be required. Hence, to save the time, gauges
are used, which can tell whether the part manufactured is within the prescribed limits or not.

NEED FOR INSPECTION
• Thus, the need for inspection can be summarized as:
1. To ensure that the part, material or component conforms to the established standard.
2. To meet the interchangeability of manufacture.
3. To maintain customer relationships by ensuring that no faulty product reaches the customers.
4. Provide the means of finding out shortcomings in manufacture. The results of inspection are not only
recorded but forwarded to the manufacturing department for taking necessary steps, so as to produce
acceptable parts and reduce scrap.
5. It also helps to purchase a good quality of raw materials, tools, equipment which governs the quality of the
finished products.
6. It also helps to coordinate the functions of quality control, production, purchasing and other departments of
the organization.
7. To take a decision on the defective parts i.e., to judge the possibility of making some of these parts
acceptable after minor repairs.

OBJECTIVES OF METROLOGY
• While the basic objective of a measurement is to provide the required accuracy at minimum cost, metrology
would have further objective in a modern engineering plant with different shops like tool room, machine shop,
press shop, plastic shop, pressure die casting shop, electroplating and painting shop, and assembly shop; as also
research, development and engineering department. In such an engineering organization, further objectives
would be as follows:
 A thorough evaluation of newly developed products, to ensure that components designed is within the process
and measuring instrument capabilities available in the plant.
 To determine the process capabilities and ensure that these are better than the relevant component tolerance.
 To determine the measuring instrument capabilities and ensure that these are adequate for their respective
measurements.
 To minimize the cost of inspection by effective and efficient use of available facilities and to reduce the cost
of rejects and rework through the application of statistical quality control techniques.

OBJECTIVES OF METROLOGY
 Standardization of measuring methods. This is achieved by laying down inspection methods for any product at
the right time when production technology is prepared.
 Maintenance of the accuracy of the measurement. This is achieved by periodical calibration of the metrological
instruments used in the plant.
 Arbitration and solution of problems arising on the shop floor regarding methods of measurement.
 Preparation of designs for all gauges and special inspection fixtures.

MEASUREMENT METHODS
• Measurement is a process of comparison of the physical quantity with a reference standard. Depending upon
the requirement and based upon the standards employed, there are two basic methods of measurement:
 Direct measurements: the value of the physical matter (measurand) is determined by comparing it directly
with reference standards. The physical quantities like mass, length and time are measured by direct
comparison. Direct measurements are not to be preferred because they involve human factors, are less accurate
and also less sensitive. Further, the direct methods may not always be possible, feasible and practicable.
 Indirect measurements: the value of the physical parameter (measured) is more generally determined by
indirect comparison with secondary standards through calibration. The measurand is converted into an
analogous signal which is subsequently processed and fed to the end device that presents the result of a
measurement. The indirect technique saves primary or secondary standards from frequent and direct handling.
• The accuracy of each approach is apparently traceable to the primary standard via secondary standard and the
calibration.

MEASUREMENT METHODS
 Primary, secondary and tertiary measurements:
• The complexity of an instrument system depends upon the measurement being made and upon the accuracy
level to which the measurement is needed.
• Based upon the complexity of the measurement system, the measurements are generally grouped into three
categories namely the primary, secondary and tertiary measurements.
• In the primary mode, the sought value of a physical parameter is determined by comparing it directly with
reference standards.
• The requisite information is obtainable through senses of sight and touch. Examples are:
1. Matching of two lengths when determining the length of an object with a ruler.
2. Matching of two colours when judging the temperature of red hot steel.
3. Estimating the temperature difference between the contents of containers by inserting fingers.
4. Use of beam balance to measure (actually compare) masses.
5. Measurement of time by counting the number of strokes of a clock.

MEASUREMENT METHODS
• The primary measurements provide subjective information only. That is, the observer can only indicate that the
contents of one container are hotter than the contents of the other; one rod is longer than the other rod; one
object contains more or less mass than the other.
• In many technological activities, it is often difficult to make direct observation of the quantity being measured.
The human senses are not equipped to make a direct comparison of all the quantities with equal facility.
Further, frequent measurements are extremely time-consuming and tedious if taken directly.
• Accordingly, we use indirect methods in which the measurand is converted into some effect which is directly
measurable. The indirect methods make comparisons with a standard through the use of a calibrated system
i.e., an empirical relation is established between the measurement actually made and the results that are desired.
• The indirect measurements involving one translation are called secondary measurements and those involving
two conversions are called tertiary measurements.

MEASUREMENT METHODS
• The conversion of pressure into displacement by means of bellow (fig. a) and the conversion of force into
displacement by means of springs (fig. b) are simple examples of secondary measurements.
• When a pressure above that of the atmosphere is applied to the open end of the bellows, these expand and the
resulting displacement is a measure of applied pressure:
(a) (b)
Fig. 1.1: Secondary measurement: (a) bellow converting pressure into
displacement (b) spring converting force into displacement

MEASUREMENT METHODS
δ = k1· P ……….(1.1)
Where, P is the variable pressure (input), δ is the bellow’s displacement (output) and k1 is the constant of
proportionality. The displacement varies linearly with applied pressure provided that the range of pressure
variation is small.
• Likewise, a spring stretches when a vertical force is applied at its free end. Different forces give rise to
different displacements and so a measure of the spring deflection gives a unique indication of the force.
δ = k2· F ……….(1.2)
Where, F is the applied force (input), δ is the spring deflection (output) and k2 is the constant of proportionality.
The identity prescribed by equation 1.2 is written as
δ = F / S ……….(1.2 a)
Where S represents the spring stiffness; it is defined as that force which is necessary for unit spring deflection.

MEASUREMENT METHODS
Fig. 1.2: Tertiary measurement: measurement of
pressure by a bourdon tube gauge
• The measurement of static pressure by a bourdon tube pressure gauge is a typical example of tertiary
measurement.
• When the static pressure (input signal) is applied to the bourdon tube, its free end deflects. The deflection
constitutes the secondary signal is very small and needs to be made larger for display and reading.

MEASUREMENT METHODS
Fig. 1.3: Tertiary measurement: measurement of
angular speed by an electric tachometer
• In the voltmeter, the voltage moves a pointer on a scale, i.e. voltage is translated into a length change. The
tertiary signal of length change is a measure of the speed of the shaft and is transmitted to the observer.
• Whereas the input to a measuring system is known as measurand, the output is called measurement.
• For example, in a bourdon tube gauge, the applied pressure (input to the measurement system) is the
measurand. The output from the system is the movement of the pointer against a calibrated scale, and this
pointer movement becomes the measurement.
• Likewise in an electric tachometer, the angular speed is measured and the movement of the pointer (length
change) is the measurement.

MEASUREMENT METHODS
 Contact and non-contact type measurements:
• Measurements may also be described as (i) contact type where the sensing element of the measuring device
has contact with the medium whose characteristics are being measured and (ii) non-contact type where the
sensor does not communicate physically with the medium.
• The optical, radioactive and some of the electrical/electronic measurements belong to this category.

PRECISION & ACCURACY
 Precision:
• The terms precision and accuracy are used in connection with the performance of the instrument. Precision
is the repeatability of the measuring process. It refers to the group of measurements for the same
characteristics taken under identical conditions.
• It indicates to what extent the identically performed measurements agree with each other. If the instrument
is not precise, it will give different (widely varying) results for the same dimension when measured again
and again.
• The set of observations will scatter about the mean. The scatter of these measurements is designated as 0,
the standard deviation. It is used as an index of precision. The less the scattering, more precise is the
instrument. Thus, the lower, the value of 0, the more precise is the instrument.
 Accuracy:
• Accuracy is the degree to which the measured value of the quality characteristic agrees with the true value.
The difference between the true value and the measured value is known as an error of measurement.
• It is practically difficult to measure exactly the true value and therefore a set of observations is made whose
mean value is taken as the true value of the quality measured.

PRECISION & ACCURACY
 The difference between Precision and Accuracy:
Fig. 1.4: Difference between precision & accuracy
• Accuracy is very often confused with precision though much different. The distinction between precision
and accuracy will become clear by the following example. Several measurements are made on a component
by different types of instruments and the results are plotted.
• In any set of measurements, the individual measurements are scattered about the mean, and the precision
signifies how well the various measurements performed by the same instrument on the same quality
characteristic agree with each other.

TYPES OF ERROR
Errors may originate in a variety of ways and the following sources need examination:
 Instrument errors:
• There are many factors in the design and construction of instruments that limit the accuracy attainable.
Instruments and standards possess inherent accuracies and certain additional inaccuracies develop with use and
time. Examples are:
1. Improper selection and poor maintenance of the instrument.
2. Faults of construction resulting from finite width of knife edges; lost motion due to necessary clearance in gear
teeth and bearings; excessive friction at the mating parts, etc.
3. Mechanical friction and wear, backlash, yielding of supports, pen or pointer drag and hysteresis of elastic
members due to aging.
4. Unavoidable physical phenomenon due to friction, capillary attraction and imperfect rarefaction.
5. Assembly errors resulting from the incorrect fitting of the scale zero with respect to the actual zero position of
the pointer, non-uniform division of the scale and bent or disorder pointers.
• The assembly errors do not alter with time and can be easily discovered and corrected. Uncertainty in
measurement due to friction at the mating parts and the pen and pointer drag is frequently reduced by gentle
tapping of the instruments; a vigorous tapping would, however, lead to delicate bearings being injured and thus
increasing friction all the more.

TYPES OF ERROR
 Environmental errors:
• The instrument location and the environment errors are introduced by using an instrument in conditions different for
which it has been designed, assembled and calibrated. The different conditions of use may be temperature, pressure,
humidity and altitude, etc.; the effect of temperature being predominant.
• A change in the temperature may alter the elastic constant of spring, may change the dimensions of a measuring
element or linkage in the system, may alter the resistance values and flux densities of magnetic elements.
• Consider a mercury-in-glass thermometer being used for the measurement of air temperature. The instrument will be
located wrongly if during measurements, the sun happens to be shining on the thermometer bulb.
• Similarly, the bulb would indicate an effect of heat radiation if the thermometer is placed too close to a window.
Likewise, high air pressure would tend to compress the walls of the bulb and force the mercury to rise within the
capillary and this give a spurious temperature reading.
• Environmental errors alter with time in an unpredictable manner. The following methods have been suggested to
eliminate or atleast reduce the environmental errors:
1. Use the instrument under the conditions for which it was originally assembled and calibrated. This may involve
control of temperature, pressure and humidity conditions.
2. Measure deviations in the local conditions from the calibrated ones and then apply suitable corrections to the
instrument readings.
3. Automatic compensation for the departures from the calibrated conditions by using sophisticated devices.

TYPES OF ERROR
 Translation and signal transmission errors:
• The instrument may not sense or translate the measured effect with complete fidelity. The error also includes the
non-capability of the instrument to follow rapid changes in the measured quantity due to inertia and hysteresis
effects.
• The transmission errors creep in when the transmitted signal is rendered faulty due to its distortion by
resonance, attenuation, loss leakage, or of being absorbed or otherwise consumed within the communication
channel.
• The error may also result from unwanted disturbances such as noise, line pick-up, hum, ripple, etc. The errors
are remedied by calibration and by monitoring the signal at one or more points along its transmission path.

TYPES OF ERROR
 Observation errors:
• There goes a saying ‘instruments are better than the people using them’. Even when an instrument has been
properly selected, carefully installed and faithfully calibrated, shortcomings in the measurement occur due to
certain failings on the part of the observer. The observation errors may be due to:
1. Parallax i.e., apparent displacement when the line of vision is not normal to the scale.
2. Inaccurate estimates of average reading, lack of ability to interpolate properly between graduations.
3. Incorrect conversion of units in between consecutive readings and non-simultaneous observation of
independent quantities.
4. Personal bias, i.e., a tendency to read high or low, or anticipate a signal and read too soon. Wrong scale
reading, and wrong recording of data.
• The poor mistakes resulting from the inexperience and carelessness of the observer are obviously remedied with
careful training and by taking independent readings of each item by two or more observers.

TYPES OF ERROR
 Operational errors:
• A pre-requisite to precise and meticulous measurements is that the instruments should be properly used. Quite
often, errors are caused by poor operational techniques. Examples are:
1. A differential type of flowmeter will read inaccurately if it is placed immediately after a valve or a bend.
2. A thermometer will not read accurately if the sensitive portion is insufficiently immersed or is radiating heat to
a colder portion of the installation.
3. A pressure gauge will correctly indicate pressure only when it is exposed to pressure which is to be measured.
4. A steam calorimeter will not give indication of the dryness fraction of steam unless the sample drawn correctly
represents the condition of steam.

TYPES OF ERROR
 System interaction errors:
• The act of measurement may affect the condition of the measurand and thus lead to uncertainties in
measurements. Examples are:
1. The introduction of a thermometer alters the thermal capacity of the system and provides an extra path for heat
leakage.
2. A ruler pressed against a body results in a differential deformation of the body relative to the ruler.
3. An obstruction type flowmeter may partially block or disturb the flow conditions. Consequently, the flow rate
shown by the meter may not be the same as before the meter installation.
4. Reading shown by a hand tachometer would vary with the pressure with which it is pressed against the shaft.
5. A milliammeter would introduce additional resistance in the circuit and thereby alter the flowing current by a
significant amount.

TYPES OF ERROR
• The job of an instrument designer is to see that the alteration due to system interference is minimal. Many of the
most precise, expensive and elaborate measuring instruments owe their cost and complexity solely to the means
adopted to eliminate or at least reduce interaction between the instrument and the physical state being measured.
• The errors discussed above may be grouped into random errors as distinguished from systematic errors. Random
errors are accidental, small and independent, and are mainly due to inconstant factors such as spring hysteresis,
stickiness, friction, noise and threshold limitations.
• The magnitude and direction of these errors cannot be predicted from a knowledge of the measurement system;
however these errors are assumed to follow the laws of probabilities. Systematic errors are repeated consistently
with the repetition of the experiment and are caused by such effects as sensitivity shifts, zero off-set and known
non-linearity.
• Systematic errors cannot be determined by direct and repetitive observations of the measurand made each time
with the same technique. The only way to locate these errors is to have repeated measurements under different
conditions or with different equipment and where possible by an entirely different method.

TYPES OF ERROR
Systematic Errors Random Errors
These errors are repetitive in nature and are of
constant and similar form.
These are non-consistent. The sources giving rise to
such errors are random.
These errors result from improper conditions or
procedures that are consistent in action.
Such errors are inherent in the measuring system or
measuring instruments.
Except for personal errors, all other systematic
errors can be controlled in magnitude and sense.
Specific causes, magnitudes and sense of these
errors cannot be determined from the knowledge of
measuring system or condition
If properly analysed, these can be determined and
reduced or eliminated.
These errors cannot be eliminated, but the results
obtained can be corrected.
These include calibration errors, variation in contact
pressure, variation in atmospheric conditions,
parallax errors, misalignment errors, etc.
These include errors caused due to variation in the
position of setting standard and workpiece, errors
due to displacement of lever joints of instruments,
errors resulting from backlash, friction, etc.

DEVELOPMENT OF MATERIAL STANDARD
• The need of establishing a standard length was raised primarily for determining agricultural land areas and for
the erection of buildings and monuments. The earliest standard of length was established in terms of parts of the
human body. The Egyptian unit was called a cubit. It was equal to the length of the forearm (from the elbow to
the tip of the finger).
• Rapid advancement made in engineering during the nineteenth century was due to improved materials available
and more accurate measuring techniques developed. It was not until 1855 that the first accurate standard was
made in England.
• It was known as the imperial standard yard. This was followed by an International Prototype meter made in
France in the year 1872. These two standards of lengths were made of a material (metal alloys) and hence they
are called material standards in contrast to wavelength standard adopted as length standard later on.

 Imperial Standard Yard:
• The imperial standard yard is made of 1-inch square cross-section bronze bar (82% copper, 13% tin, 5% zinc)
which is 38 inches long. The bar has two ½ inch diameter × ½ inch deep holes. Each hole is fitted with a 1/10th
inch diameter gold plug. The top surface of these plugs lies on the neutral axis of the bronze bar.

 Imperial Standard Yard:
• The purpose of keeping the gold plug lines at the neutral axis has the following advantages:
1. Due to bending of beam, the neutral axis remains unaffected.
2. The plug remains protected from accidental damage.
• The top surface of the gold plugs is highly polished and contains three lines engraved transversely and two lines
longitudinally.
• The yard is defined as the distance between two central transverse lines on the plugs when,
1. The temperature of the bar is constant at 62˚ F.
2. The bar is supported on rollers in a specified manner to prevent flexure.

 International Standard Meter (Prototype):
• This standard was established originally by the International Bureau of Weights and Measures in the year 1875.
The prototype meter is made of platinum-iridium alloy (90% platinum and 10% iridium) having a cross-section
as shown in the figure below.

• The metric standard when in use is supported at two points which are 58.9 cm apart as calculated by Airy’s
formula, according to which the best distance between the supporting points is given by
b = L / {√(n2 – 1)}
where, L = total length of bar (assumed uniform)
b = distance between points
n = number of points
• For prototype meter,
b = 102 / {√(22 – 1)} = 58.9 cm
• This reference was designated as International Prototype Meter M in 1899. It is preserved by BIPM at Sevres in
France. The BIPM is controlled by the International Committee of Weights and Measures.

 Disadvantages of Material Standard:
1. The material standards are influenced by the effects of variation of environmental conditions like temperature,
pressure, humidity and aging, etc. and it thus changes the length.
2. These standards are required to be preserved or stored under security to prevent their damage or destruction.
3. The replica of these standards was not available for use somewhere else.
4. These are not easily reproducible.
5. The conversion factor was to be used for changing over to metric working.
6. Considerable difficulty is experienced while comparing and verifying the size of gauges.

 Wavelength Standard:
• The major drawback with the metallic standards meter and yard is that their length changes slightly with time.
Secondly, considerable difficulty is experienced while comparing and verifying the sizes of gauges by using
material standards.
• This may lead to errors of unacceptable order of magnitude. It, therefore, became necessary to have a standard
length which will be inaccurate and invariable. Jacques Babinet, a French philosopher, suggested that
wavelength of monochromatic light can be used as a natural and invariable unit of length.
• In 1907, the International Angstrom (A) unit was defined in terms of the wavelength of red cadmium in dry air
at 15˚ C (6438.4696 A = 1 wavelength of red cadmium). Seventh General Conference of Weights and Measures
approved in 1927, the definition of the standard of length relative to the meter in terms of the wavelength of the
red cadmium as an alternative to International Prototype meter.
• Orange radiation of isotope krypton-86 was chosen for a new definition of length in 1960, by the Eleventh
General Conference of Weights and Measures. The committee decided to recommend that Krypton-86 was the
most suitable element and that it should be used in a hot-cathode discharge lamp maintained at a temperature of
63° Kelvin.

 Wavelength Standard:
• According to this standard meter was defined as equal to 1650763.73 wavelengths of the red-orange radiation of
Krypton isotope 86 gases.
• The standard as now defined can be reproduced to an accuracy of about 1 part in 109. The meter and yard were
redefined in terms of the wavelength of orange Kr-86 radiation as,
1 meter = 1650763.73 wavelengths, and
1 yard = 0.9144 meter
= 0.9144 x 1650763.73 wavelengths
= 1509458.3 wavelengths.

 Meter (as of today):
• Although the Krypton-86 standard served well, technologically increasing demands more accurate standards. It
was through that a definition based on the speed of light would be technically feasible and practically
advantageous. Seventeenth General Conference of Weights and Measure. I agreed to a fundamental change in
the definition of the meter on 20th October 1983.
• Accordingly, a meter is defined as the length of the path traveled by light in a vacuum in 1/299792458 seconds.
This can be realized in practice through the use of an iodine-stabilized helium-neon laser.
• The reproducibility is 3 parts in 1011, which may be compared to measuring the earth's mean circumference to an
accuracy of about 1 mm. With this new definition of the meter, one standard yard will be the length of the path
traveled by lightly traveled in 0.9144 × 1/299792458 sec. I. e., in 3 x 10-9 sec.

 Meter (as of today):
• The advantages of wavelength standard are:
1. It is not a material standard and hence it is not influenced by the effects of variation of environmental conditions
like temperature, pressure, humidity, and aging.
2. It need not be preserved or stored under security and thus there is no fear of being destroyed as in the case of
meter and yard.
3. It is not subjected to destruction by wear and tear.
4. It gives a unit of length which can be produced consistently at all times in all the circumstances, at all the places.
In other words, it is easily reproducible and thus identical standards are available with all.
5. This standard is easily available to all standardizing laboratories and industries.
6. There is no problem with transferring this standard to other standards meter and yard.
7. It can be used for making comparative measurements of very high accuracy. The error of reproduction is only of
the order of 3 parts in 1011.

 Subdivision of standards:
• The international standard yard and the international prototype meter cannot be used for general purposes. For
practical measurement, there is a hierarchy of working standards. Thus depending upon their importance of
accuracy required, for the work the standards are subdivided into four grades:
1. Primary standards
2. Secondary standards
3. Tertiary standards
4. Working standards

 Primary standards:
• For a precise definition of the unit, there shall be one, and only one material standard, which is to be preserved
under most careful conditions. It is called the primary standard. International yard and International meter are
examples of primary standards. A primary standard is used only at rare intervals (say after 10 to 20 years) solely
for comparison with secondary standards. It has no direct application to a measuring problem encountered in
engineering.
 Secondary standards:
• Secondary standards are made as nearly as possible exactly similar to primary standards as regards design,
material, and length. They are compared with primary standards after long intervals and the records of deviation
are noted. These standards are kept at a number of places for safe custody. They are used for occasional
comparison with tertiary standards whenever required.
 Tertiary standards:
• The primary and secondary standards are applicable only as ultimate control. Tertiary standards are the first
standard to be used for reference purposes in laboratories and workshops. They are made as a true copy of the
secondary standards. They are used for comparison at intervals with working standards.

 Working standards:
• Working standards are used more frequently in laboratories and workshops. They are usually made of low grade
of material as compared to primary, secondary and tertiary standards, for the sake of economy. They are derived
from fundamental standards. Both line and end working standards are used. Line standards are made from an H-
cross-sectional form.
• Most of the precision measurement involves the distance between two surfaces and not with the length between
two lines. End standards are suitable for this purpose. For shorter lengths, up to 125 mm slip gauges are used
and for longer lengths end bars of the circular cross-section is used. The distance between the end faces of slip
gauges or end bars is controlled to ensure a high degree of accuracy.
• Sometimes the standards are also classified as:
1. Reference standards- used for reference purposes.
2. Calibration standards - Used for calibration of inspection and working standards.
3. Inspection standards - Used by inspectors.
4. Working standards - Used by operators, during working

LINE AND END MEASUREMENTS
• A length may be measured as the distance between two lines or as the distance between two parallel faces. So, the
instruments for direct measurement of linear dimensions fall into two categories:
1. Line Standards
2. End Standards
 Line Standards:
• When the length is measured as the distance between centers of two engraved lines, it is called line standard. Both
material standards yard and meter are line standards. The most common example of line measurements is the rule with
divisions shown as lines marked on it.
 Characteristics:
1. Scales can be accurately engraved but the engraved lines themselves possess thickness and it is not possible to take
measurements with high accuracy.
2. A scale is quick and easy to use over a wide range.
3. The scale markings are not subjected to wear. However, the leading ends are subjected to wear and this may lead to
undersize measurements.
4. A scale does not possess a "built-in" datum. Therefore it is not possible to align the scale with the axis of
measurement.
5. Scales are subjected to parallax error.

 End Standards:
• When a length is expressed as the distance between two flat parallel faces, it is known as end standard.
Examples: Measurement by slip gauges, end bars, ends of micrometer anvils, vernier calipers, etc. The end faces
are hardened, lapped flat and parallel to a very high degree of accuracy.
 Characteristics:
1. These standards are highly accurate and used for measurement of close tolerances in precision engineering as
well as in standard laboratories, tool rooms, inspection departments, etc.
2. They require more time for measurements and measure only one dimension at a time.
3. They are subjected to wear on their measuring faces.
4. Group of slips can be "wrung" together to build up a given size; faulty wringing and careless use may lead to
inaccurate results.
5. End standards have built-in datum since their measuring faces are f l at and parallel and can be positively
locked on the datum surface.
6. They are not subjected to parallax effect as their use depends on feel.

Sr. No. Characteristic Line Standard End Standard
1. Principle Length is expressed as the distance between two lines Length is expressed as the distance between two
flat parallel faces
2. Accuracy Limited to ± 0.2mm for high accuracy, scales have to
be used in conjunction with magnifying glass or
microscope.
Highly accurate for measurement of close
tolerances up to ± 0.001 mm.
3. Ease & time of
measurement
Measurement is quick and easy The use of end standards requires skill and is
time-consuming.
4. Effect of wear Scale markings are not subject to wear. However,
significant wear may occur on leading ends. Thus it
may be difficult to assume zero of scale as a datum.
These are subjected to wear on their measuring
surfaces.
5. Alignment It cannot be easily aligned with the axis of
measurement.
Can be easily aligned with the axis of
measurement.
6. Manufacture & cost Simple to manufacture at a low cost. The manufacturing process is complex and the
cost is high.
7. Parallax effect They are subjected to parallax error They are not subjected to parallax error
8. Examples Scale (yard, meter etc.) Slip gauges, end bars, V-caliper, micrometers etc.

LINEAR MEASUREMENT
• Linear measurement means the measurement of perpendicular distance between two points or surfaces. The
linear measurement applies to the measurement of length, heights, diameters, thicknesses, radius, etc.
• The linear measurement instrument is designed either for line measurements or end measurements. The line
measuring instruments consists of a series of accurately spaced painted or marked lines on them.
• For example, the scale is a line measuring instrument, the dimension to be measured is aligned with the
graduations of the scale. The end measuring instruments measure the distance between two end surfaces. The
micrometer and slip gauges are an example of end measurement instruments.
 Classification of Linear Measuring Instruments:
 Classification based on methods of measurement:
1. Direct Measuring Instruments
2. Indirect Measuring Instruments
 Classification based on the accuracy that can be obtained:
1. Non-precision type instruments
2. Precision type instruments
Graduated Instruments
Non-graduated Instruments

ENGINEER’S STEEL RULE OR SCALE
• The steel rule or scale is the simplest line measuring instrument. The common machinist's scale is made of
hardened steel or stainless steel and is accurately graduated in mm or inch division as shown in the figure below.
• It works on the basic measuring technique of comparing on Unknown length to the one previously calibrated.
The scales are manufactured in different sizes and styles. The scale is available in 150 mm, 300 mm, 600 mm
and 1000 mm lengths.
• The least count of scale or smallest division on the scale is generally 1/2 mm on millimeter scales and 1/100 inch
on inch scales. Dimensions smaller than the least count may be measured by a visual estimate of the distance.

CALIPERS
• In some cases, the dimensions of a component cannot be measured by the only scale. In these cases, the calipers
use with scale for transferring the length (measured) to the scale.
• The caliper consists of two legs which hinged at top and ends of legs span the part to be inspected, as shown in
the figure below. The legs of the caliper are made from carbon and alloy steels.
• In modem precision measurement calipers are not employed where high accuracy is required, but in skilled
hands, they will remain extremely useful.

CALIPERS
• Classification of calipers:
1. Based on the design aspect:
a. Finn joint calipers
b. Spring type calipers
2. Based on their use:
a. Outside calipers
b. Inside calipers
c. Transfer calipers
d. Odd leg calipers
• Firm joint calipers work on the friction created at the junction of legs. The legs may become loose after certain
use, but can be adjusted easily. This type of calipers is used for mass production measurements.

CALIPERS
• The spring caliper is a modification of a firm joint caliper in which the two legs carry a curved spring at the top, fitted
in the notches.
• The tendency of the spring is to force the legs apart and the distance between them can be adjusted by applying the
pressure against the spring pressure by tightening the nut. The spring calipers are more accurate and permit an accurate
sense of touching in measuring.
• Outside calipers: It is used for measuring diameters, thicknesses, and other outside dimensions by transforming the
readings to the scale, vernier caliper or micrometer.
• Inside calipers: It is used for measuring hole diameters, the distance between shoulders, etc.
• Transfer calipers: It is used to measure recessed areas from which the legs of · caliper cannot be removed. An
auxiliary mm is provided to preserve the original setting after the legs are collapsed.
• Odd leg calipers: It is used for finding centers of circular jobs, marking a line parallel to a true edge and many other
types of marking operations.

VERNIER CALIPER
• Vernier caliper is one of the common instruments in which the small distance (measured) is magnified by
auxiliary (vernier) scale. The vernier caliper works base on the vernier principle. Vernier principle: When two
scales (main and auxiliary scales) or division slightly different in size are used, the difference between them can
be utilized to enhance the accuracy of the measurement.
 Construction:
• It consists of two-scale as one is fixed, called main scale and other movable, called vernier scale as shown in the
figure below. The main scales are calibrated on an L-shaped frame and integral with a fixed jaw.
• The vernier scale is calibrated on a sliding jaw which slides over the main scale. The vernier caliper parts are
made of good quality steel and measuring tips or face are hardened to reduce wear.

VERNIER CALIPER
 Construction:
• For a precise setting of the movable jaw, an adjustment screw is provided with a movable jaw. The vernier is
also facilitated to lock the sliding scale with the fixed main scale.
 Working:
• Generally, when two jaws touch each other, zero lines on the main scale coincides with zero on a vernier scale.
If it is not so, there is zero error that must be accounted for in the final reading. Hence before using an
instrument, it should be check for zero error. The work to be measured is kept between the jaws for measuring
the outside dimensions as shown in the figure above. The fine adjustment can be done by an adjustment screw.
After the fine adjustment, the movable jaw is made fixed on the main scale frame by clamping screw. Then
vernier caliper is taken from workpiece for taking the readings from the main as well as the vernier scale. To
obtain the reading the number of divisions on the main scale is first read off. The vernier scale is then examined
to determine which of its division coincides or most coincident with a division on the main scale.

VERNIER CALIPER
 Working:
• It is observed, zero marks of vernier scale lie between 13 and 14 division marks of the main scale. It means that
the diameter to be measured is more than 13 and less than 14. Also, the 21st vernier division coincides exactly
with the main scale division.
The diameter of cylinder =Main scale reading + (No. of vernier division coinciding with the main scale x least count)
= 13 mm + (21 x 0.02)
= 13 mm + 0.42
= 13.42 mm

VERNIER CALIPER
 Types of vernier calipers:
• According to Indian Standard (IS): 3651-1974, three types of vernier calipers have been specified to measure
external and internal dimensions up to 2000 mm with the least count (accuracy) of 0.02, 0.05 and0.1 mm. These
are available in ranges of: 0-125 mm, 0-200 mm, 0-300 mm, 0-500 mm, 0-750 mm, 0-1000 mm, 750- 1500mm
and 1500-2000 mm. As per IS, the types of vernier calipers:
• Type-A: This type of vernier has a jaw on both sides for external and internal measurements and a blade for
depth measurements as shown in the figure above.
• Type-B: This type of vernier has a single pair of the jaw, one side of jaws for external and another side of jaws
for internal measurements as shown in the figure above.
• Type-C: This type of venire has a jaw on both sides, one side jaws for external and internal measurements. Other
side jaws are used for marking operations as shown in the figure.
A-type B-type C-type

VERNIER CALIPER
 Precautions to be taken in use of vernier caliper:
• No play should be there between sliding and fixed jaws. If play exists then the accuracy of the vernier caliper will
be lost.
• Normally the tips of measuring jaws are worn and that must be taken into account.
• Use the stationary jaw on the reference point and obtain a measured point by sliding the movable jaw.
• The vernier caliper must always be properly balanced in hand and held lightly the sliding jaw through adjusting
the screw. Do not push the moving jaw under pressure, use adjusting screw for fine adjustment.
• In case of measuring an outside diameter, be sure that the caliper bar and the plane of caliper jaws are truly
perpendicular to the work piece's longitudinal centerline.
 Errors in vernier caliper:
• Errors due to play between the sliding jaw and fixed scale bar.
• Zero error due to wear and wrapping of jaws.
• Errors due to incorrect observation of scale readings.
• Errors clue to excessive force on moving jaw.
• Errors are also introduced if the line of measurement does not coincide with the line of the scale.

VERNIER HEIGHT GAUGE
• The vernier height gauge is shown in the figure below is another common vernier principle-based instrument
used for accurate measurements and marking of vertical heights above a surface plate datum.
• It can also be used to measure differences in heights by taking the vernier scale readings at each height and
determining the difference by subtraction. It can be used for a number of applications in the tool room and
inspection department.

 Construction:
• The vernier height gauge is similar to a vernier caliper except that the fixed jaw, in this case, is replaced by a
fixed base that rests on a surface plate or table when taking measurements. The base is massive and robust in
construction to ensure rigidity and stability.
• A vertical graduated column is supported on a massive base. The sliding jaw is attached to the sliding vernier
head. The sliding vernier head is facilitated with clamping and fine adjustment screws.
• The sliding jaw carries a removable clamp that can carry a measuring jaw or a scriber. The upper and lower
surfaces of the measuring jaw are parallel to the base so that it can be used for measurements over or under a
surface. The scriber when attached, venire is used for inspection of parts and for layout work.
• The scriber can be used for scribing lines at a specified distance above the surface. The scriber may in some cases
be replaced by a dial indicator. This provides an easy and exact reading of slider movement by dial gauges which
is larger and clear. All parts of the gauge are made of good quality steel or stainless steel.

 Precautions to be taken in use of vernier height gauge:
• The height gauge should be kept in its case when not in use.
• It should be tested for straightness, squareness, and parallelism of working faces of the beam, measuring jaw and
scriber.
• When using a gauge, care must be taken to ensure that the base is clean and free from burrs.
• The springing of measuring jaw should be always avoided.
• For taking a final reading, the sliding jaw should be locked to the vertical column by locking the screw.

VERNIER DEPTH GAUGE
• Fine adjustment screw Vernier scales a vernier depth gauge as shown in the figure below, used for measuring
depths of holes, slots, recesses, and distances from a plane surface to a projection.
 Construction:
• It consists of a vernier scale and the main scale. The vernier scale is graduated to the main body of the depth
gauge. The main scale is graduated on the long blade on which sliding head of vernier scale slides.
• The gauge also having a fine adjustment and locking screws. While using the depth gauge, the base is held firmly
on the reference surface. Before using a gauge, first of all, make sure that the reference surface on which the
depth gauge base is rested is satisfactorily true, flat and square. Then lower the blade into the hole until it contacts
the bottom surface of the hole. The final adjustment depending upon the sense of contact feel is made by the fine
adjustment screw.

VERNIER DEPTH GAUGE
 Construction:
• The sliding head locked on the blade (main scale) by tightening the locking screw. The instrument is removed
from the hole and reading taken from the main scale and vernier scale the same way as vernier caliper.
• The depth gauge sliding head and long blade are made from good quality steel or stainless steel. It is carefully
made so that the blade is perpendicular to the base in both directions. The end of the beam is square and flat, like
the end of a steel rule and the base is flat and true, free from curves or waviness.

MICROMETERS
• A micrometer is another useful device for magnifying small measurement. In micrometer, the accurate screw and
nut are used for measurement. The micrometers having good accuracy (about 0.01 mm), hence is used for most
engineering precision work.
 Principle:
• Micrometers works on the principle of screw and nut. The screw is attached to a concentric cylinder or thimble
the circumference of which is divided into a number of equal parts. We know that when a screw is turned through
a nut by one revolution, its axial movement is equal to the pitch of the thread of a screw.
• If I am pitch or lead of screw-in mm, each rotation of screw advances it in relation to the internal threads a
distance equal to I mm. If the circumference of the concentric cylinder is divided into n equal divisions,
movement (rotation) of a cylinder through one division indicates 1/n rotation of the screw or 1/n mm axial
advance.
• In millimeter micrometer instruments the screw has a pitch (lead) of 0.5 mm and thimble has 50 divisions so that
the least count of the micrometer is equal to 0.5/50 =mm. By reducing the pitch of the screw thread or by
increasing the number of divisions on the thimble, the axial advance value per one circumferential division can be
reduced and the accuracy of measurement can be increased.

MICROMETERS
 Construction:
• Fig. 1.21 shows an outside micrometer is used to measure the outside diameter with accuracy 0.01 mm. It
consists of (i) U-shaped frame, (ii) Anvil, (iii) Spindle, (iv) Thimble, (v) Barrel or sleeve, (vi) Rachet and (vii)
Locknut.
• The U-shape frame made of steel, cast iron or light alloy and holds all the components of a micrometer. The gap
between the two ends of the U-shape frame permits a maximum diameter or length of a job to be measured.
• The one end of the spindle is attached to the thimble and the other end constitutes the movable anvil. The screw
threads made on the spindle with a specified pitch. The screw-threaded spindle passes the barrel which acts as a
nut to engage screw threads.
• The fixed anvil is fixed on the left side of the U-shape frame. The barrel is accurately divided and clearly marked
in a 0.5 mm division along its length which serves as the main scale. The thimble can be moved over the barrel
when it rotates with a screw thread spindle during the axial advance of the spindle. The thimble has 50 equal
divisions around its circumference.

MICROMETERS
 Construction:
• Each division having a value of 0.5mm/50 = 0.01 mm. The job to be measured is located between the fixed anvil
and the end of the spindle. When anvil and spindle ends are brought together the instrument reads zero. The
ratchet is provided at the end of the thimble.
• It is used to assure accurate measurement, and to prevent too much pressure being applied to the micrometer.
When the spindle reaches near the work surface to be measured the operator uses the rachet screw to tighten the
thimble.
• The rachet automatically slips when the correct (uniform) pressure is applied and prevents the application of too
much pressure. A lock nut is provided on the micrometer spindle to lock it when the micrometer is at its correct
reading.

MICROMETERS
 Procedure for measuring dimension with the help of micrometer:
• Select a micrometer with a desired range of measurement.
• Check the micrometer for zero error. It can be check by contacting the faces of anvil and spindle. The zero on the
thimble should coincide with zero on the reference line on the barrel (main scale), as shown in the figure. If this
does not happen, then zero error is present in the micrometer which must be accounted for in final readings.
• Hold workpiece which dimension to be measured between anvil and spindle as shown in the figure below. Then
make a final adjustment by rachet and lock it with the help of lock nut.

MICROMETERS
 Procedure for measuring dimension with the help of micrometer:
• Now, take the reading of the main scale, suppose main scale reading is 13 mm as shown in Fig. 1.24. Take the
thimble reading which coincides with the reference line on the barrel. The 35th division line is coincident with
the reference line.
Total reading = Main scale reading + (L.C. x reading on thimble)
= 13.5 + 0.01 X 35
= 13.850 mm

MICROMETERS
 Sources of errors in micrometers:
• The faces of anvil and spindle may not be truly flat.
• Lack of parallelism and squareness of anvil or spindle at some or all parts of the scale.
• The setting of zero reading may be inaccurate.
• Inaccurate readings have shown by fractional divisions on the thimble.
• Wear on the faces of anvil & spindle, and wear in the threads of the spindle.
• Error due to too much pressure on the thimble or not using the ratchet.

MICROMETERS
 Precautions to be taken while using a micrometer:
• The micrometer is available in various sizes and ranges, and the corresponding micrometer should be selected
depending upon the size of the workpiece.
• Micrometer should be cleaned of any dust and spindle should move freely.
• Check and set the zero reading before measuring.
• The workpiece whose dimension is to be measured must be held in the left hand and micrometer in the right hand.
• Make sure that the dimension to be measured in parallel to the axis of the spindle and the anvil.
• Always use the rachet for final adjustment and locknut for taking readings.
• In case of measurement of diameter make sure that the anvil and spindle faces touch the maximum dimension
only.

MICROMETERS
 Types of Micrometers:
There is a number of different micrometers available for specific application and accuracy.
1. Outside micrometer
2. Inside micrometer
3. Vernier micrometer
4. Depth micrometer
5. Bench micrometer
6. Digital micrometer
7. Differential screw micrometer
8. Micrometer with dial gauge
9. Screw thread micrometer

MICROMETERS
 Inside Micrometer:
• The inside micrometer is used to measure the internal dimensions of the workpiece. Figure below shows the
inside micrometer, the construction is similar to the outside micrometer. However, the inside micrometer has no
U-shape frame and spindle. The measuring tips are constituted by the jaws whose faces are hardened and ground
to a radius.
• One one of the jaw is held stationary at the end and the second one moves by the rotation of the thimble. The
locking arrangement is provided with a fixed jaw. Figure below shows another inside micrometer is used for a
larger internal dimension. It consists of two anvils, sleeve, thimble, rachet, stop and extension rods.

MICROMETERS
 Inside Micrometer:
• The range of this micrometer is 50 mm to 210 mm. however, the range can be increased by anyone extension rod
provided with it. This micrometer has no frame and spindle. The measuring points are at Extreme ends provided
with anvils. The axial movement of endpoints is taken place by thimble rotation about the barrel axis.
• A series of extension rods are provided in order to obtain a wide measuring range. Before taking the
measurement, the approximate internal dimension of a workpiece (whose dimension is to be measured by inside
micrometer) is measured by a scale.
• The extension rod is then selected to the nearest one and inserted in a micrometer head. Then, the micrometer is
checked for zero error with the help of a standard-sized specimen whose internal dimension is known. The
micrometer is then adjusted at a dimension slightly smaller than the internal (bore) diameter of the workpiece.
• The micrometer head is then held finely against the bore as shown in the figure above and other contact surface is
adjusted by moving the thimble till the correct feel is sensed. The micrometer is then removed and reading is
taken. The lengths of extension rod and collar are added to the micrometer reading.

MICROMETERS
 Vernier Micrometer:
• In order to increase accuracy, the vernier principle also is applied to an outside micrometer. This type of
micrometer can be read by 0.001 mm length.
• The vernier micrometer as shown in the figure consists of three scales as follows:
1. The main scale is graduated on the barrel with two sets of division marks. The set below the reference line reads
in mm and set above the line reads in 1/2 mm.
2. A thimble scale is graduated on the thimble with 50 equal divisions. Each small division of thimble represents
1/50 of a minimum division of the main scale. The main scale minimum division value is 1/2 mm.
3. Vernier scale is marked on the barrel. There are 10 divisions on the barrel and this is equivalent to 9 divisions on
the thimble. Hence one division on a vernier scale is equal to 9/10 that of thimble. But one division on the
thimble is equal to 0.01 mm. Therefore, one division on a vernier scale is equal to 0.009 mm.

MICROMETERS
Least count of vernier micrometer:
L.C. = Value of smallest division on thimble- Value of smallest division on the vernier scale.
= 0.01 - 0.009
= 0.001 mm
Hence accuracy of the vernier micrometer is 0.001 mm.
Reading the vernier micrometer:

MICROMETERS
Reading the vernier micrometer:
Main scale reading= 11.5 mm Thimble reading
= No. of thimble division coinciding with reference line x L.C. of a thimble
= 12 x 0.01
= 0.12 mm
The 4th vernier scale line is coincident with the divisions of a thimble Hence, vernier reading
=No. of vernier division coinciding with thimble scale x L.C. of vernier
= 6 x 0.001
= 0.006 mm
Total reading= 11.5 + 0.12 + 0.006
= 11.626 mm
If vernier line coincident with the reference line is 0, then no vernier reading added to the final reading.

MICROMETERS
 Depth Micrometer:
• Depth micrometer (micrometer depth gauge) is used to measure the depth of holes, slots and recessed areas.
• It consists of a base (measuring face) which is fixed on the barrel and measuring spindle which is attached with
thimble as shown in the figure below. The axial movement of the spindle takes place by rotation of thimble.
• The measurement is made between the end face of the spindle and the measuring face of the base. As spindle
moves away from the base, the measurement increases due to scales on the barrel are reversed from the normal.

MICROMETERS
 Depth Micrometer:
• The scale indicates zero when spindle flush with the face and maximum when the spindle is fully extended from
the base Figure above shows the use of depth micrometer.
• The main scale reading is 17. The 14thdivision line of the thimble match with the reference line. Hence, thimble
reading is
Total reading= 17 + 0.14 = 17.14 mm
• The depth micrometer is available in ranges 0-25 mm or 0-50 mm. The range can be increased up to 0-90 mm by
using extension rods in steps of 25 mm. The extension rod can easily be inserted by removing the spindle cap.

MICROMETERS
 Differential Screw Micrometer:
• Differential screw micrometer uses differential screw principle and hence the accuracy of -this micrometer is increased
compared to an ordinary micrometer.
• In this micrometer, the screw has two types of pitches as shown in the figure, one smaller and other larger, instead of
one uniform pitch as in ordinary micrometer.
• Both the screws are right-handed and the screws are so arranged that the rotation of thimble, one screw. Moves forward
and other move backward. The anvil is not attached to the thimble, but it slides inside the barrel.
• The smaller screw nut is fixed in the anvil while larger screw nut fixed with a barrel, hence screw rotates with the
thimble. In the case of a metric micrometer, the normally employed pitch for the screws is 0.4 mm and 0.5 mm.
• Therefore, one revolution of the thimble, the measuring anvil will advance by an amount equal to 0.5-0.4 = 0.1 mm.
The thimble circumference is graduated in 100 equal divisions. Hence anvil moves in an axial direction by mm
corresponding one division of thimble this micrometer has a smaller range due to small total axial movement
(differential axial movement) of the spindle.

MICROMETERS
 Digital Micrometer:
• The mechanical measuring device as micrometer and vernier are suitable for making measurements that are
accurate within 0.001 mm. This device is inexpensive, lightweight, compact and relatively rugged.
• But when greater accuracy of measurement is desired, these mechanical devices are inadequate. In the case of
digital or electronic instruments, measuring instruments having an electronic digital readout has become common
in the industrial measuring instrument in order to get superior precision and ease of reading provided by the
electronic digital readout.
• A digital micrometer consists of the frame, anvil, spindle, locknut, barrel, thimble, ratchet, LCD display and
ON/OFF ZERO key as shown in the figure below. 1t has incorporated a digital readout into the structure of the
micrometer's body.

MICROMETERS
 Digital Micrometer:
• The digital readout is integrated with a rotary encoder that is capable of reading the axial displacement of a
spindle which rotates as a thimble is rotated.
• The digital micrometers are available in a large number of different sizes, normally 0-25 mm, 25-50 mm, 50- 75
mm, and 75-100 mm. They are used to measure length, diameter or thickness.

BORE GAUGES
 Dial Bore Gauge:
• The bore gauges are used to measure the small bores. There are different types of bore gauges are used to
measure the small diameter of the bore. However, the hemispherical bore gauge and dial bore gauge are the most
common for industrial use.
• The dial or vernier bore gauge measures a bore directly. This gauge work on the proven principle of two
diametrically opposed measuring points, one fixed and other moving.
• The gauge consists of one fixed measuring head and one movable measuring head as shown in the figure below.
The measuring body is connected with the dial indicator body by tube. The pushrod is provided inside the tube in
order to transmit the movement of movable measuring head to dial indicator.

BORE GAUGES
 Dial Bore Gauge:
• Hence the horizontal movement of the rod is transmitted into a vertical direction and dial indicator which gives
an indication of the variation of size.
• The accuracy of this bore gauge is 0.001 mm. normally, this gauge used to measure the dimensional variation
inside an injection molding or an extruder barrel. Dial bore gauges allow rapid and accurate checking of a bore
for size, ovality, taper and wear within a deep bore.

BORE GAUGES
 Hemispherical Bore Gauge:
• This gauge consists of spring steel arms having hemispherical ends as shown in the figure.
• Inside the arm, a wedge-shaped member attached to the spindle can be moved endwise by rotating the screw
head. Due to up and down the wedge member with a spindle, the hemispheric ends expand or contract as per the
size of the bore.
• Then the gauge is taken out and the reading noted down by measuring over the hemispheres with a micrometer.
These bore gauges are available in four sizes to measure from 3 mm to 12 mm diameter of the bore.

BORE GAUGES
 Telescopic Gauge:
• A telescopic gauge is an indirect measuring device and used for measuring the internal diameter of holes, slots,
and grooves, etc. Telescopic gauge as shown in the figure below consists of a handle, two telescopic rods, and a
locking screw.
• One end of the handle is connected with a tube in which the telescopic rods slide. The telescopic rods having
spherical contacts.
• These telescopic rods are forced apart by an internal spring. For taking the measurement, the telescopic rods are
compressed against spring and inserted into the hole whose diameter to be measured, then extended to touch the
walls of the hole.

BORE GAUGES
 Telescopic Gauge:
• They are then locked in position by means of a locking screw. The telescopic gauge is then taken out from the
hole and the size of the extended rods can be measured with a micrometer or vernier caliper to determine the
diameter of the hole.
• The telescopic gauge typically used to check or measure the diameter of the cylinder in case of the internal
combustion engine in which the cylinder's piston would extend and retract.

SLIP GAUGES
• Slip gauges are also known as gauge blocks. These may be used as reference standards for transferring the
dimension of the unit of length from the primary standard to gauge blocks of lower accuracy and for the
verification and graduation of measuring apparatus.
• They are universally accepted end standard of length in the industry. A slip gauge is a rectangular block as shown
in the figure below made up of high grade hardened steel with two opposite faces separated by a defined distance.
• The slip gauge having a cross-section (w x l) of about 9 mm x 30 mm for sizes up to 10 mm and 9 mm x 35 mm
for larger sizes. These blocks are hardened to resist wear and carefully stabilized so that they are independent of
any subsequent variation in size or shape.
• They are then stabilized by heating and cooling successively in stages so that hardening stresses are removed.
After being hardened they are carefully finished by high grade lapping to a high degree of finish, flatness, and
accuracy.
• The opposite faces are of such a high degree of surface finish so that when the blocks are pressed together with a
slight twist by hand, they will wring together. They will remain firmly attached to each other.

SLIP GAUGES
• The slip gauges are classified according to their accuracy as:
1. AA: For master slip gauges,
2. A: For reference purpose
3. B: For working slip gauges.
• Indian standard specifications for slip gauges (IS 2984-1966) specify grades as follows:
1. Reference grade: These slip gauges are used as standards by manufacturers of slip gauges.
2. Calibration grade: These slip gauges are used where the highest level of accuracy is required in normal
engineering practice. These gauges are used with a comparator to calibrate the other slip gauges.
3. Grade-00: These slip gauges are placed in the standard room and used for the highest precision work as
checking other lower grade slip gauges (Grade I and II).
4. Grade-0: These slip gauges are used for inspection of jobs in the quality control department where high
precision is required.
5. Grade l: These slip gauges are used for general-purpose manufacturing gauges in applications like tool, gauges
and component production.
6. Grade II: These slip gauges are used for rough setting purposes and checking of components having wide
tolerances. These are also known as workshop grade. Slip gauges are generally available in sets. The exact
number of the piece in each set may vary from manufacturer to manufacturer. The following two sets (45 or 87
pieces) of slip gauges are in general uses as follows. The slip gauges themselves are subjected to wear with use
and must be checked periodically against standard gauge blocks or more precise measuring standards.

SLIP GAUGES
Manufacture of Slip Gauges:
The following operations are carried out to obtain the required qualities in slip gauges during manufacture.
Step -1: The approximate size of slip gauges is made by preliminary operations.
Step -2: The blocks are hardened and wear-resistant by a special heat-treatment process.
Step -3: For stabilization of the whole life of blocks, the seasoning process is carried out.
Step -4: The approximate required dimension is done by a final grinding process.
Step -5: Lapping operation is carried out to get the exact size of slip gauges.
Step -6: Comparison is made with grandmaster sets.
Slip gauges accessories:
• The slip gauges can be used for any purpose without the help of any accessories, however, the application of slip
gauges can be increased by providing accessories to the slip gauges. The following various accessories are used with
slip gauges:
1. Measuring jaw: It is available in two designs specially made for internal and external features.
2. Scriber and Centre point: It is mainly formed for marking purposes.
3. Holder and base: Holder is nothing but a holding device used to hold a combination of slip gauges. The base is
designed for mounting the holder rigidly on its top surface. It is made of robust construction and designed such that it
remains stable when used with the longest size holder.

SLIP GAUGES
Material for gauge blocks:
• The material used for gauge blocks must have excellent wear resistance, size stability and ability to take the
extremely fine surface finish.
• Tool steel, chrome-plated steel, stainless steel, tungsten carbide, chrome carbide, and Cervit are some of the
materials used for gauges. Of these, tungsten carbide, chrome carbide, and Cervit are the most interesting cases.
• Depending upon the material used the slip gauges may be heat treated to obtain size stability and required degree
of hardness. The surface is lapped to obtain the desired smoothness and accuracy.
• The carbide block is very hard and therefore does not scratch easily. The finish of the gauging surfaces is as good
as steel, and the lengths appear to be at least as stable as steel, perhaps even more stable.
• Tungsten carbide has a very low expansion coefficient and because of the high density, the blocks are heavy.
Chrome carbide has an intermediate thermal expansion coefficient and is roughly the same density as steel.
• Carbide blocks have become very popular as master blocks because of their durability and because in a controlled
laboratory environment the thermal expansion difference between carbide and steel is easily manageable.
• Cervit is a glassy ceramic that was designed to have nearly zero thermal expansion coefficient. The drawbacks
are that the material is softer than steel, making scratches a danger, and by nature the ceramic is brittle.

SLIP GAUGES
Wringing of slip gauges:
• If two slip gauge blocks are wrung together to each other as shown in the figure below, and considerable pull is
required to break the wring.
• This phenomenon of wringing occurs due to molecular adhesion between a liquid film (not more than 6 to 7
microns thick) and the mating surfaces.
• This wringing process is used to build up to desired dimensions over a range of sizes in specific increments. The
success of the wringing operation depends upon the surface finish and flatness of the blocks used and the absence
of dirt, grease, burrs, and scratches.
• When the slip gauges are correctly wrung together, the error in the total length is negligible.

SLIP GAUGES
Application of slip gauges:
1. They are used to check the accuracy of vernier, micrometers and other measuring devices.
2. They are used to set the comparator to a specific dimension.
3. They are used for direct precise measurement where the accuracy of the workpiece is important.
4. They are frequently used with a sine bar to measure the angle of the workpiece.
5. They can be used to check the gap between parallel locations.
Calibration of slip gauges:
• The slip gauges are liable to show signs of wear after an appreciable period of use due to handling in the
laboratory or inspection room. Hence they should be checked or recalibrated at regular intervals.
• Workshop and inspection grade gauges are calibrated by direct comparison against calibration grade gauges with
the help of a comparator. A variety of comparators are available such as mechanical, optical and pneumatic
comparators.
• Eden Rolt millionth comparator and Brook level comparator have been specially designed for slip gauges.
Various forms of interferometers and optical flat are applicable to measuring gauge block flatness.
• Interferometers are optical instruments used for measuring flatness and determining the length of the slip gauges
by direct reference to the wavelength of light. The parallelism between the faces of a gauge block can be
measured in two ways; with interferometry or with an electro-mechanical gauge block comparator.

LIMIT GAUGES
• Gauges are inspection tools that serve to check the dimensions of the manufactured parts. Limit gauges ensure the
size of the component lies within the specified limits. They are non-recording and do not determine the size of the
part.
• Gauges are generally classified as:
1. Standard gauges are made to the nominal size of the part to be tested and have the measuring member equal in
size to the mean permissible dimension of the part to be checked.
2. Limit Gauges are also called 'GO' and 'NO GO' gauges. These are made to the limit sizes of the work to be
measured. One of the sides or ends of the gauge is made to correspond to the maximum and the other end to the
minimum permissible size. The function of limit gauges is to determine whether the actual dimensions of the
work are within outside the specified limits.
• A GO-NO GO gauge is a measuring tool that does not return the size in the conventional sense but instead returns
a state.
• The state is either acceptable (the part is within tolerance and may be used) or it is unacceptable (and must be
rejected).
• They are well suited for use in the production area of the' factory as they require little skill or interpretation to use
effectively and have few, if any, moving parts to be damaged in the often hostile production environment.

LIMIT GAUGES
Why are Limit Gauges necessary?
• In the manufacturing firm, the components are manufactured as per the specified tolerance limits, upper limit and
lower limit. The dimension of each component should be within this upper and lower limit.
• If the dimensions are outside these limits, the components will be rejected. If we use any measuring instruments
to check these dimensions, the process will consume more time. Also, in mass production, we are not interested
in knowing the amount of error in dimensions.
• It is just enough whether the size of the component is within the prescribed limits or not. For this purpose, limit
gauges are used. A limit gauge is not a measuring gauge, this gives the information about the products which may
be either within the prescribed limit or not.
• By using the limit gauges report, the control charts of P and C charts are drawn to control the invariance of the
products. This procedure is mostly performed by the quality control department of each and every industry. The
limit gauge is mainly used for checking for cylindrical holes of identical components with a large number in mass
production.

LIMIT GAUGES
The basic concept of Gauge design (Taylor’s Principle):
• According to Taylor, 'GO' and 'NOGO' gauges should be designed to check maximum and minimum material
limits. The terms minimum metal condition and maximum metal condition are used to describe the tolerance state
of a workpiece.
• The GO gauge is made near the maximum metal condition. The GO gauge must be able to slip inside/over the
feature without obstruction. For example plug gauge (for checking hole size), as shown in the figure below
having exactly the GO limit.
• Diameter and a length equal to the engagement length of the fit to be made for checking the GO limit of the
workpiece and this gauge must perfectly assemble with the workpiece to be inspected.
• The NO GO gauge is made near the minimum metal condition. NO, GO gauge which contacts the workpiece
surface only in two diametrically opposite points and at those points, it should have exactly NO GO limit
diameter.

LIMIT GAUGES
Types of Limit Gauges:
 According to their purpose:
 Workshop gauges: Working gauges are those used at the bench or machine in gauging the work as it is made.
 Inspection gauges: These gauges are used by the inspection personnel to inspect manufactured parts when finished.
 Reference or Master gauges: These are used only for checking the size or condition of other gauges.
 According to the form of tested surfaces:
 Plug gauges: They check the dimensions of a hole.
 Ring gauges: They check the dimensions of a shaft.
 Snap gauges: They also check the dimensions of a shaft. Snap gauges can be used for both cylindrical as well as non-
cylindrical work as compared toting gauges which are conveniently used only for cylindrical work.
 According to their design:
 Single limit & double limit gauges
 Single-ended and double-ended gauges
 Fixed & adjustable gauges

LIMIT GAUGES
 Plug gauges:
• Plug gauges are used for checking holes and consist of two cylindrical wear-resistant plugs. The plug made to the
lower limit of the hole is known as 'GO' end and this will enter any hole which is not smaller than the lower limit
allowed.
• The plug made to the upper limit of the hole is known as 'NO GO' end and this will not enter any hole which is
smaller than the upper limit allowed. The plugs are arranged on either end of a common handle.
• The ends are hardened and accurately finished by grinding. One end is the GO end and the other end is NO GO
end. If the size of the hole is within the limits, the GO end should go inside the hole and NO GO end should not
go.
• If the GO end does not go, the hole is undersized and also if NO GO end goes, the hole is oversized. Hence, the
components are rejected in both cases.
• The GO end and NO GO end are arranged on both the ends of the plug as shown in the figure below. This type
has the advantage of easy handling and is called double-ended plug gauges.

LIMIT GAUGES
 Plug gauges:
• In the case of a progressive type of plug gauges as shown in the figure below, both the GO end and NO GO end
are arranged on the same side of the plug.
• We can use the plug gauge ends progressively one after the other while checking the hole. It saves time.
Generally, the GO end is made longer than the NO GO end in plug gauges.
• As shown in the figure below, taper plug gauges are used to check tapered holes. It has two check lines, one is a
GO line and another is a NO GO line.
• During the checking of work, NO GO line remains outside the hole and GO line remains inside the hole. They
are various types of taper plug gauges are available as taper plug gauge- plain, taper plug gauge- tanged, taper
ring gauge- plain and taper ring gauge- tanged.

LIMIT GAUGES
 Ring gauges:
• Ring gauges are used for checking the diameter of shafts. They are used in a similar manner to that of GO and
NO GO plug gauge. A ring gauge consists of a piece of metal in which a hole of the required size is bored as
shown in the figure below.
• The hole or bore is accurately finished by grinding and lapping after taking the hardening process. The hole of
GO ring gauge is made to the upper limit size of the shaft and NO GO for the lower limit. The periphery of the
ring is knurled to give more grips while handling the gauges.
• Nominally, the GO ring gauge and NO GO ring gauge are separately used to check the shaft. Generally, NO GO
made with a red mark or a small groove cut on its periphery in order to identify NO GO gauge.

LIMIT GAUGES
 Snap gauges:
• Snap gauges are used for checking external dimensions. They are also called as gap gauges. A snap gauge usually
consists of a plate or frame with a parallel faced gap of the required dimension.
• Snap gauges can be used for both cylindrical as well as non-cylindrical work as compared to ring gauges which
are conveniently used only for cylindrical work.
• A double-ended snap gauge as shown in the figure below is having two ends in the form of anvils. The GO anvil
is made to lower limit and NO GO anvil is made to an upper limit of the shaft. This snap gauge is also known as
solid snap gauges.
• If both GO and NO GO anvils are formed at the same end as shown in the figure below, then it is called
progressive snap gauge. It is mainly used for checking large diameters up to 100 mm. The GO anvil should be at
the front and NO GO anvil at the rear.

LIMIT GAUGES
 Snap gauges:
• So, the diameter of the shaft is checked progressively by these two ends. This type of gauge is made of
horseshoe-shaped frame with an I section to reduce the weight of the snap gauges. This snap gauge is also called
a caliper gauge.
• An adjustable snap gauges as shown in the figure below consists of one fixed anvil and two small adjustable
anvils. The distance between the two anvils is adjusted by adjusting the adjustable anvils by means of set screws.
• This adjustment can be made with the help of slip gauges for specified limits of size. They are used for checking
large-size shafts.

ANGULAR MEASUREMENTS
Introduction:
• The angle is defined as the opening between two lines which meet at a point. If one line is moved around a point
in an arc, a complete circle can be formed and it is from this circle that units of angular measurement are derived.
• If a circle is divided into 360 parts, each part is called a degree (˚). Therefore angle is such a thing which be just
generated very easily requiring no absolute standard, and it is the precision with which circle can be divided to
get the correct measure of an angle.
• Each degree is divided into 60 minutes (') and each minute into 60 seconds ("). This method of defining angular
units is called a sexagesimal system, which is used for engineering purposes.
• The unit of angle derived from theoretical considerations is the radian, defined as the angle subtended at the
center of a circle by an arc length equal to the radius of the circle. Thus the angle subtended by the complete
circumference will be 2π radians.

PROTRACTORS
• The following types of protractors are generally used for angular measurements:
1. Vernier bevel protractor
2. Optical bevel protractor
 Vernier bevel protractor:
• The angle between two faces of a component can be simply measured by means of a protractor. Vernier bevel
protractor is probably the simplest instrument for measuring the angle between two faces of component. It
consists of (i) main body, (ii) base plate stock, (iii) adjustable blade, (iv) circular plate containing vernier scale,
(v) acute angle attachment.

PROTRACTORS
• The figures above show a simple vernier bevel protractor and vernier bevel protractor with acute angle
attachment. The acute angle attachment enables very small angles to be measured.
• The base plate is attached to the main body, and an adjustable blade is attached to a circular plate containing a
vernier scale. The main scale graduated in degrees is provided on the main body. The adjustable blade is capable
of rotating freely about the center of the main scale engraved on the body of the instrument.
• The base of the base plate is made flat so that it could be laid flat upon the work for any type of angle to be
measured.
• The blade can be moved along throughout its length and can also be reversed. It is about 150 or 300 mm long, 13
mm wide and 2 mm thick.
• The ends of the blades are ground off at 45° and 60° for working incomers and to act directly as meter gauges.
The blades and stock should be hardened and tempered to reduce wear.

PROTRACTORS
• The principle of the vernier bevel protractor is shown in the figure below. A vernier scale is provided with the
main scale. The main scale on the protractor is divided into degrees from 0° to 90° each way.
• The vernier scale is divided up so that 12 of its divisions occupy the same space as 23° on the main scale as
shown in figure, so vernier division = 23°/12 = 1°55’0”.
• Since two divisions on the main scale equal2 degrees of arc, the difference between two divisions on the main
scale equals 2 degrees of arc, the difference between two divisions on the main scale and one division on the
vernier scale is (2° - 1°55'0") = 5' or 5 minutes of arc.
• Thus the reading of the vernier bevel protractor equals: The largest ‘whole’ degree on the main scale+ the reading
on the vernier scale in line with the main scale division.

PROTRACTORS
• The reading in the figure give above is:
= Main scale reading, 51° + Vernier 45 mark in line with the main scale
= 51°45'

PROTRACTORS
 Optical bevel protractor:
• The recent development of the bevel protractor is an optical bevel protractor. In this device, a glass circle divided
at 10 minutes intervals throughout the circle is fitted inside the body. A small microscope is fitted through which
the circle graduations can be viewed.
• The adjustable blade is clamped to a rotating member which carries its microscope. With the aid of a microscope,
it is possible to read by estimation to about 2 min.
• The scale is graduated as a full circle marked 0 to 90°-0 to 90°. The zero position corresponds to the condition
when the blade is parallel to the stock. Provision is also made for adjusting the focus of the system to
accommodate nominal variation in eyesight.
• The scale and vernier are so arranged that they are always in focus in the optical system. Figure below shows the
optical bevel protractor.

SINE BARS
• Sine bar is a precision angle measuring instrument used along with slip gauges. It is used to measure the angles
very accurately and or to locate the work to a given angle.
 Construction:
• Sine bars are made from high carbon, high chromium, corrosion-resistant steel, suitably hardened, precision
ground and stabilized.
• Two cylinders of equal diameters are attached at the ends. The axes of these two cylinders are mutually parallel to
each other and also parallel to and at an exact distance from the upper surface of the sine bar.
• The center to center distance between the rollers or plugs is available for fixed distance i.e. L= 100 mm, 200 mm,
250 mm, 300 mm. The diameter of the plugs or roller must be of the same size and the center distance between
them is accurate.
• The important condition for the sine bar is that the surface of the sine bar must be parallel to the center lines of
the roller.

SINE BARS
 Construction:
• Some holes are drilled in the body of the sine bar to reduce the weight and to facilitate handling. Figure above
shows the nomenclature for sine bars as recommended by IS: 5359-1969.
 Working Principle:
• The principle of operation of the sine bar relies upon the application of trigonometry. One roller of the bar is
placed on the surface plate and the combination of slip gauges is inserted under the second roller for setting a
given angle.
• If ‘h’ is the height of the combination of slip gauges and 'L' the distance between the centers of the rollers. Then,
sin θ = (h / L) or θ = sin-1 (h / L)
• Thus the angle to be measured or to be set is determined by the indirect method as a function of sine, for this
reason, the device is called a 'sine bar'.

SINE BARS
 Accuracy requirements of a sine bar:
1. The rollers must be of equal diameter and true geometric cylinders.
2. The distance between the roller axes must be precise and known, and these axes must be mutually parallel.
3. The upper surface of the bar must be flat and parallel with the roller axes, and equidistant from each other.
 Use of sine bar:
 Locating any work to a given angle:
• As we have discussed in the working principle of the sine bar,
sin θ = (h / L), where h = height of slip gauge combination
L = distance between the centers of the rollers
θ = angle to be set
• Thus, knowing θ, ‘h’ can be found out and any work could be set at this angle; as the top face of the sine bar is
inclined at angle θ to the surface plate.
• For better results, both the rollers could also be placed on slip gauges of height h1 and h2 respectively.

SINE BARS
 Checking or measuring unknown angles:
 When the component is of small size:
• Figure below shows how the sine bar is used to check small components that may be mounted upon it. The dial
gauge is mounted upon a suitable stand then set at one end of the work and moved along the upper surface of the
component.
• If there is a variation in a parallelism of the upper surface of the component and the surface plate, it is indicated
by the dial gauge. The combination of the slip gauges is so adjusted that the upper surface of the component is
truly parallel with the surface plate.

SINE BARS
 When the component is of small size:
• The angle of the component is then calculated by the relation,
θ = sin-1 (h / L)
 When the component is of large size:
• When the component is too large to be mounted on the sine-bar, the sine-bar can often be mounted on the
component as shown in the figure below.
• The height over the rollers can then be measured by a vernier height gauge; using a dial test gauge mounted on
the anvil of height gauge to ensure constant measuring pressure.

SINE BARS
• This is achieved by adjusting the height gauge until the dial gauge shows the same zero reading each time. The
difference between the two height gauge readings being the rise of the sine-bar as shown and
sin θ = (R1 – R2) / L
• Another arrangement of determining an angle of large size part is shown in the figure below.
• The component is placed over a surface plate and the sine bar is set up at an approximate angle on the component
so that its surface is nearly parallel to the surface plate.

SINE BARS
• A dial gauge is moved along the top surface of the sine bar to note the variation in parallelism. If' h' is the height
of the combination of the slip gauges and 'dh' the variation in parallelism over distance ‘L’.
• It is impractical to use a sine bar for angle above 45°, as beyond this angle the errors due to the center distance of
rollers, and gauge blocks, being in error, are much magnified.
 Sources of Error:
1. Error in the measurement of center distance of two precision rollers.
2. Error inequality of size of rollers and cylindrical accuracy in the form of the rollers.
3. Error in a geometrical condition of measurement like the flatness of the upper surface of the bar, the parallelism
of roller axes with each other, a parallelism between the gauging surface and plane of roller axes, etc.
4. Error in slip gauge combination used for angle setting.

SINE BARS
 Advantages:
1. It is a precise and accurate angle measuring device.
2. It is simple in design and construction.
3. It is easily available.
 Disadvantages:
1. It is fairly reliable at angles less than 15° but becomes increasingly inaccurate as the angle increases. It is
impractical to use a sine bar for an angle above 45°.
2. It is difficult to handle and position the slip gauges.
3. The sine bar is physically clumsy to hold in position.
4. The application is limited for a fixed center distance between two rollers.
5. Slight errors of the sine bar cause larger angular errors.

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 the testing of conical work, centered at each end as shown in the figure below.
• These are extremely useful since the alignment accuracy of the centers ensures that the correct line of
measurement is made along the workpiece.
• The centers can also be adjusted depending on the length of the conical workpiece, to behold between centers.
The procedure for its setting is the same as that for the sin bar. Figure below shows sine table, which is the most
convenient and accurate design for heavy work-piece.

SINE CENTRE
• It consists of a self-contained sine bar, hinged at one roller and mounted on its datum surface.
• The work is held axially between centers, the angle of inclination will be half the included angle of the work. The
necessary adjustment is made in the slip gauge height and the angle is calculated as
θ = sin-1 (h / L)

ANGLE GAUGES
• The first set of combinations of angle gauges was developed by Dr. Tomlinson of N.P.L in 1941. The slip gauges
are built up to give a linear dimension, the same way as the angle gauges can be built up to give a required angle.
• These gauges enable any angle to be set to the nearest 3'' These are pieces of hardened and stabilized steel. The
measuring faces are lapped and polished to a high degree of accuracy and flatness.
• These gauges are about 76 mm long and 16 mm wide and are available in two sets. One set consists of 12 pieces
and a square block, in three series of values of angle viz,
1°, 3°, 9°,27°, and 41°
1', 3', 9' and 27', and
6'', 18'', and 30”
• Another set contains 13 pieces and a square block.
1°, 3°, 9°,27°, and 41°
1', 3', 9' and 27', and
3'', 6’’, 18'' and 30''

ANGLE GAUGES
• All these angle gauges in combination can be added or subtracted as shown in the figure below, thus, making a
large number of combinations is possible.
• Each angle gauge is accurate to within one second and is marked with engraved V which indicates the direction
of the inclined angle.
• Angle gauges have been widely used in engineering industries for the quick measurement of angles between two
surfaces. Frequent use of these gauges is to check whether the components are within its off-angle tolerance.
• Where the angle to be measured between the two surfaces exceeds 90°, the use of precision square becomes
essential. The reflective properties of their lapped surfaces make them particularly suitable for use with
collimating type of instruments.
 Limitations:
• The block formed by the wringing (combination) of a number of these gauges become bulky and cannot always
be conveniently applied to work, so they are more suitable for reference along with other angle measuring
devices.
• Errors are easily compounded when they are wrung in combination.

SPIRIT LEVEL
• A spirit level, as shown in the figure, is generally thought of as a device used for static leveling of machinery and
other equipment but a calibrated spirit level is a very useful instrument for measuring small angle relative to a
horizontal datum with high precision.
• The spirit level essentially consists of a simple glass tube, the bore of which is ground to a large radius. If a liquid
almost fills the tube, the bubble in the liquid will always be at the highest position in the tube. If the tube is tilted
through a certain angle, the bubble will move •along the radius of the tube through a distance proportional to the
angle of the tilt.
• If the movement of the bubble is measured with the help of a scale provided on the glass tube, the angle of the tilt
can be measured accurately.

Ch 1 introduction to metrology, linear and angular measurement

Ch 1 introduction to metrology, linear and angular measurement

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Ch 1 introduction to metrology, linear and angular measurement

Similar to Ch 1 introduction to metrology, linear and angular measurement (20)

Recently uploaded

Recently uploaded (20)

Ch 1 introduction to metrology, linear and angular measurement