Measurements and Measuring Tools

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Measurements and Measuring Tools

• Measuring can be considered to be the most
  important process in engineering. Without the
  ability to measure accurately, we cannot
• Mark out components (Marking out is, essentially,
  drawing on metal so as to provide guide lines for
  a fitter or a machinist to work to).
• Set up machines correctly to produce components
  to the required size and shape.
• Check components whilst we are making them to
  ensure that they finally end up the correct size
  and shape.
• Inspect finished components to make sure that
  they have been correctly manufactured.

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Linear measurement

• When you measure length, you measure the shortest
  distance in a straight line between two points,
  lines or faces.
• It doesnt matter what you call this distance
  (width, thickness, height, breadth, depth or
  diameter) it is still a measurement of length.
• Measurement of length is the comparison of the
  size of a component or a feature of a component
  and a known standard of length.

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Steel rules

• The steel rule is frequently used in workshops
  for measuring components of limited accuracy
  quickly. The quickness and ease with which it can
  be used, coupled with its low cost, makes it a
  popular and widely used measuring device.
• Metric rules may be obtained in various lengths
  from 150 mm to 1000 mm (1 metre).
• Steel rules may be rigid or flexible
  depending upon their thickness and the temper
  of the steel used in their manufacture.
• When choosing a steel rule the following points
  should be looked for. It should be
• Made from hardened and tempered, corrosion
  resistant spring steel.
• Engine divided. That is, the graduations should
  be precision engraved into the surface of the
  metal.
• Ground on the edges so that it can be used as a
  straight edge when scribing lines or testing a
  surface for flatness.
• Ground on one end so that this end can be used
  as the zero datum when taking measurements from a
  shoulder.
• Satin chrome finished so as to reduce glare and
  make the rule easier to read, also to prevent
  corrosion.

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two faces using a steel rule and a tool bit as
an abutment
two scribed lines
two faces using a hook rule
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Calipers and their use
Calipers are used in conjunction with a rule so
as to transfer the distance across or between the
faces of a component in such a way as to reduce
sighting errors. Firm-joint calipers are usually
used in the larger sizes and spring-joint
calipers are used for fine work. The accurate
use of calipers depends upon practice,
experience, and a highly developed sense of feel.
When using calipers, the following rules should
be observed Hold the caliper gently and near
the joint. Hold the caliper square (at right
angles) to the work. No force should be used to
spring the caliper over the work. Contact
should only just be felt. The caliper should be
handled and laid down gently to avoid disturbing
the setting. Work should be stationary when
taking measurements. This is essential for safety
and accuracy.
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Vernier calipers

• Calipers are tools used in home, small shop, and
  industrial settings.
• They are used to make precise length
  measurements.
• There are three types of calipers.
• The vernier caliper.
• The dial caliper.
• The digital electronic caliper.

The vernier caliper.
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• The dial caliper

The digital electronic caliper.
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Use
Construction
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The VERNIER Scale (0.1mm)

• Notice that 10 divisions of the Vernier scale
  have the same length as 9 divisions of the main
  scale. The smallest division on the main scale is
  1mm so the divisions on the Vernier scale are
  09mm each.
• Precision 1mm - 0.9mm 0.1mm

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The VERNIER Scale (0.02mm)

• Precision 0.5mm - 0.048mm 0.02mm

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Examples
Ans. 169 0.1 4 169.4 mm
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• Although more slow to use and rather more
  difficult to read, the vernier caliper has three
  main advantages over the micrometer caliper.
• One instrument can be used for measurements
  ranging over the full length of its main (beam)
  scale.
• It can be used for both internal and external
  measurements.. Remember that for internal
  measurements you have to add the combined
  thickness of the jaws to the scale readings.
• One instrument can be used for taking
  measurements in both inch units and in metric
  dimensional systems.

• The measuring accuracy of a vernier caliper
  tends to be of a lower order than that obtainable
  with a micrometer caliper because
• It is difficult to obtain a correct feel with
  this instrument due to its size and weight.
• The scales can be difficult to read accurately
  even with a magnifying glass.

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Micrometer

• Most engineering work has to be measured to much
  greater accuracy than it is possible to achieve
  with a rule, even when aided by the use of
  calipers. To achieve this greater precision,
  measuring equipment of greater accuracy and
  sensitivity has to be used. One of the most
  familiar measuring instruments used in
  engineering workshops is the micrometer. The
  constructional details of a typical micrometer
  are shown in Fig..

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Inside Micrometer Caliper
Depth Gage Micrometer
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METRIC MICROMETER

• The figure below shows a 0.01-millimeter outside
  metric micrometer
• Note The thimble has a scale that is divided
  into 50 parts. One revolution of the thimble
  moves 0.5 millimeter on the barrel side. A
  movement of one graduation on the thimble equals
  1/50 of 0.5 millimeter along the barrel

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METRIC VERNIER MICROMETER

• The figure below shows a flattened view of a
  metric vernier micrometer
• Reading a metric vernier micrometer is the same
  as reading a 0.01mm micrometer except for the
  addition of reading the vernier scale. The
  vernier scale consists of five divisions. Each
  division equals one-fifth of a thimble division,
  or 0.002 millimeter

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Examples
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Gauge blocks
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Slip gauges are blocks of steel that have been
hardened and stabilized by heat treatment. They
are ground and lapped to size to very high
standards of accuracy and surface finish. They
are the most accurate standards of length
available for use in workshops.
Measurement Ranges (mm) Jump (mm) No of gauge blocks
1.0005 1
From 2.005 to 2.009 0.001 9
From 2.01 to 2.49 0.01 49
From 0.5 to 9.5 0.5 19
From 10 to 100 10 10
Sum 88 block
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Example (2)
Example (1)
29.874 - 2.004 27.87 -
2.37 25.5 - 5.5 20 - 20
00
16.9955 -
1.0005 15.995 - 2.005 13.99 - 2.49
11.5 - 1.5 10 - 10 00
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Measuring angles

• Angles are measured in degrees and fractions of a
  degree. One degree of arc is 1/360 of a complete
  circle. One degree of arc can be subdivided into
  minutes and seconds (not to be confused with
  minutes and seconds of time)

Right angles
The try-square (a), its use (b) and (c)
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Angles other than right angles (plain bevel
protractor)
The plain bevel protractor (a), and its use in
checking angles (b)
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Angles other than right angles (vernier
protractor)