Laboratory1 Engineering Measurement

Laboratory 1: Dimensional Measurement
L a b o ra t o ry 1
Engineering Measurement
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Objectives
• Students are required to understand the principles and the use of engineering
measurements by employing different measuring tools and methods in order to suit
the desired applications.
• To understand the meaningful of the measured values in engineering applications.
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1. Literature Review
1.3 The significance of engineering measurement
Historically, measurement was invented by human in order to facilitate their life in the
society; for example, measuring of their body sizes for costume tailoring, weighing of food and
commercialdizes as well as locating places or telling distance for commuting, etc. The linear
measurement was first invented by the Egyptian called the Egyptian Royal Cubit, which was used in
construction and agricultural at the time. The most well-known evidence is the record found in the
Palermo stone showing the height of the flooding along the Nile River. Moreover, body parts were
normally used as references to give dimensions, for example, finger, hand, arm and foot as shown in
fig. 1.
Figure 1: Body parts used as dimension references [1].
In present, dimensional measurement is of importance in engineering points of view as it is
influencing the corrected engineering design, the calculation of engineering applied loads on
structural parts and components as well as the fabrication of the desired parts. Therefore, engineers
should concern about the principle and procedure of dimensional measurement in order to obtain the
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corrected and meaningful values. Apart from 1-dimensional measurement, there are also 2dimensional and 3-dimensional measurements, which are depending on particular applications. This
is for example, measuring of the diameter and the length of structural steel rod or 3-dimensional
measurement of cast products. The precision of the measured values relies on the specific used which
required different levels of accuracy along with the measuring tools or devices utilized.
Universal measuring units can be referred from different system such as Imperial system,
Metric system and International System of Unit (SI). Imperial unit (English unit) was first developed
in Britain and covering the commonwealth countries as well as in the United State. The Imperial
system is currently replaced by the Metric system. However, several measuring units still remain in
use, for example, yard, mile or ounce, pound and ton. Table 1 illustrates the Imperial system which
can be converted into the Metric system.
The Metric system is mainly expressed in meter and gram such as distance and weight
measurement or electrical properties. The main advantage of the Metric system is that it consists of
the single base unit, which can be practically converted into many different units for measuring the
physical or mechanical properties. For instance, the length measuring unit can be expressed in
micron, millimeter, meter, or kilometer when multiplying by the factor of power of ten. For example,
the values in meter are multiplied by 10-3 and 103 are to achieve the units of millimeter and kilometers
respectively.
The SI unit was abbreviated from the French terms called Système International d'Unités,
which is now well-known for everyday uses as well as engineering and science. The SI unit was
developed from the Metric system and other units which have not been included in the Metric system
are now added. The SI unit comprises of 4 basic unit, which are as follows
1. Meter, m, which is the unit of length
2. Second, s, which is the unit of time
3. Kilogram, kg, which is the unit of mass
4. Kelvin, K, which is the unit of temperature
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Therefore, dimensional measurement is considered to be a significant impact in engineering
point of view. Standardized measuring techniques are required for universal interpretations. Errors of
the measured values can be due to either human error, precision of measuring devices, the measuring
techniques employed or even rounding up of each of the measured values for scientific calculation. If,
for example, the calculation of the velocity of an apple falling from a height of 1 meter is required, the
weight of the apple (kg) and the gravity force (~9.8 m/s2) are to be known. The accuracy of the latter
value depends on the location relevant to the sea level including the decimal used in the calculation.
Moreover the falling time of the apple within one meter height is somehow difficult to be measured.
Using stopped watch might lead to human errors. Hence, dimensional measurements especially for
scientific and engineering uses are of importance in order to minimize the possible errors to occur.
1.2 Vernier calipers measurement
A vernier caliper is quite practical for linear-dimensional measurement of parts or
components. It provides a precision to a hundred of a millimeter (10 micrometers) Fig. 2 illustrates
schematic of a typical vernier caliper which is composed of the outside and inside jaws (for external
and internal measurement respectively), the depth probe (for depth measurement), the main scale and
the vernier (displayed in metric and inch) and also the retainer (for blocking the moving part)
a) Dial caliper
b) Digital caliper
Figure 2: Vernier Calipers
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wikimedia.org
1 - Outside jaws: used to take external measures of objects
2 - Inside jaws: used to take internal measures of objects
3 - Depth probe: used to measure the depth of objects
4 - Main scale (cm)
5 - Main scale (inch)
6 - Vernier (cm)
7 - Vernier (inch)
8 - Retainer: used to block movable part
Figure 3: Details of a Vernier Caliper
In order to measure an object, reading scale are required to set at a zero position as shown in
fig. 3 a). The object is placed in the measuring position while the retainer helps to keep the object in
place during taking the measurement. The vernier caliper normally includes the metric and inch
scales on the bottom and top part of the scale as depicted in fig. 4. By reading in a metric scale, the
first line on the left indicates the location of the measured value to be read. In this case, the scale can
be read as 1.2x cm. The second decimal can be found at the position when both lines on the top and
the bottom are in line, which is the third line from the left. Therefore, the value will be read as 1.23
cm. The calipers are available in vernier, dial or digital types. The dial type is practical when zeroing
the position is required. The digital calipers offer a serial data output in which the values can be
transferred onto a personal computer. Different ways of vernier measurments are displayed in fig. 5.
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Figure 4: Vernier Caliper reading scale.
Figure 5: Different ways for vernier caliper measurement.
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1.3 Micrometer measurement
Micrometer measurement as shown in fig. 6 is considered to give a more accurate measured
value than that obtained by using a vernier calipers. Apart from the micrometer in which the scale can
be read manually, a more conveniently used-digital type is now commonly available. As
demonstrated in fig. 7, the measuring device is composed of the frame, anvil (for the sample to rest
against), spindle (moving toward the spindle by the screw), the barrel or the sleeve (containing the
scale), the lock nut (for tightening the spindle stationary), the thimble (for turning the spindle) and the
ratchet stop (locating at the end of the thimble for limiting the applied pressure by slipping at a
calibrated torque).
www.design-technology.org/micrometer.jpg
Figure 6: Micrometers
Figure 7: Detail of a micrometer
To begin the measurement, zero position of the reading scale is required before placing an
object in between the measuring rods. Locking the position using the retainer as the measurement is
taken. For reading in a metric scale, the spindle has two threads for 1 millimeter. The reading scale
on the barrel is graduated with 1 millimeter divisions and 0.5 millimeter subdivisions. The thimble
has 50 graduations each being 0.01 millimeter. Therefore, the measured value can be read as the
number of division displayed on the barrel plus the particular division visible on the thimble which
coincides with the axial line on the barrel. For example, as shown in fig 8 a), five divisions on the
barrel plus one subdivision can be read on the barrel. On the thimble, twenty eight graduations are
inline with the straight line on the barrel. This means the measured value is 5 + 0.5 + 0.28 = 5.78
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millimeters. Fig. 8 b) show a more precision reading with the third decimal horizontally displayed on
the vernier above the main scale. In such a case, the reading can be taken as 5 + 0.5 + 0.28 + 0.003 =
5.783 millimeters.
wikipedia.org
a) Barrel = 5 divisions + 0.5 subdivision
b) Barrel = 5 divisions + 0.5 subdivision
Thimble = 0.28
Thimble = 0.28
Total = 5.78 mm
Vernier = 0.003
Total
= 5.783 mm
Figure 8: Micrometer measurement
1.4 Dial gauge measurement
The dial gauge or the probe gauge is known as the results are displayed or magnified on the
dial and is used for linear displacement along the axis. The measuring ranges normally vary from
0.25 to 300 mm, with graduations of 0.001 to 0.01 in metric scale. The gauge is primarily used for
machine setups, inspection process of the machined parts or measuring the deflection of the beam or
rings. The gauges provide in inch and metric scales and the graduation styles give the positive values
(clockwise) and the negative values (counter-clockwise).
The dial gauge comprises the graduated dial face, a needle, a smaller clock-face and a loaded
probe (plunger) as shown in fig. 9. The dial face can be rotated to any position relevant to the user or
to set the gauge to zero. The needle on the main dial face indicates small increments while the needle
in a smaller clock-face indicating the number of the needle rotation on the main dial. The loaded
probe is displaced normal to the object being measured either in retracting or extending in relevant to
the referent body.
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The tips of the probe are in various size and shape depending on their applications. The small
sphere tip provides consistent measurement as it moves along an arc while the size of the tip can be
varied to allow measuring a small hole. A flat tip is also used depending on the required applications.
However the contact angle of the tip must be 90o against the object surface, if not the correction factor
is needed.
Figure 9: Dial gauges.
1.5 Surface roughness measurement
Surface roughness is an engineering parameter which significantly affects chemical, physical
and mechanical properties, tribology as well as the life of the components or parts in services.
Ground, machined or polished surfaces provides different values of surface roughness values. The
surface roughness indicates the texture of the surface, which is quantified by the vertical deviations of
the real surface from the ideal form. Large deviation infers a rough surface whist small deviations
signifies a smoother surface. The device called surface roughness testing machine used to determine
surface roughness as demonstrated in fig. 10. The roughness profile can be obtained by the tracking
the movement of the probe (tip) along the surface as shown in fig. 11. As the probe moves along the
surface the vertical displacement is recorded to produce a 2D measurement as shown in line 6) over a
measurement length which can either be a straight line of an arc circle. In order to achieve a 3D
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surface roughness measurement, the probe is conducted to travel along a 2D area on the surface as
shown in fig. 11 c).
misutoyo
Figure 10: Roughness testing machine.
wikipedia.org
1) DCantilever, 2)- Tip, 3)-Movement direction, 4)-Vertical position being recorded,
5)-surface being measured and 6)- Roughness profile
a) Schematic showing probe movement onto measured surface
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wikipedia.org
b) A sketch showing the probe travelling on a straight line along the surface (2D measurement).
3d-shape.com
c) A 3D roughness profile
Figure 11: Measuring the surface roughness.
There are various roughness parameters such as Ra, Rz , Rq , Rks, each of which reduce all of
the information derived from the roughness profile in to one single number. The most commonly
used parameter is Ra. These values are greatly influenced by how the raw profile data is filtered and
how the mean line is calculated. By convention, any capital R with a subscript is used to represent 2D
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roughness parameters whereas any capital S with a subscript is used for 3D roughness parameter.
Table 1 summarizes 2D roughness parameters together with its description and formula.
Table 1: 2D roughness parameters
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2. Materials and equipment
2.1 Test specimens
2.2 Vernier caliper
2.3 Micrometer
2.4 Dial gauge
2.5 Roughness testing machine
3. Experimental procedure
3.1 Measure two pieces of machined parts using vernier caliper and micrometer. Report the
measured values by sketch drawings of the two parts.
3.2 Measure dimensional changes of the objects provided using a dial gauge. Report the
obtained values.
3.2 Conduct the roughness test on the given sample surfaces. Record and interpret the data.
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4. Results
4.1 Dimensional measurement (Drawing No.1)
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4.2 Dimensional measurement (Drawing No.2)
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4.3 Dial gauge measurement
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4.4 Surface roughness measurement
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5. Discussion
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6. Conclusions
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7. Questions
7.1 For measuring the dimensions of the machined parts, the thickness of the paper and the
displacement of the beam during defection, which measuring technique you would like to
employ? Explain in each case in details.
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7.2 From roughness experimental result, please indicate which samples would provide better
fatigue performance. Give reason.
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8. References
8.1 Dieter, G.E., Mechanical metallurgy, 1988, SI metric edition, McGraw-Hill, ISBN 0-07100406-8.
8.2 www.wikipedia.org
8.3 www.mitutoyo.com
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