Measuring Tools

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Measuring Tools
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Introduction

• Measuring tools for small engines are divided
  into three categories.
• Direct reading
• Measurement transferring
• Reject gages

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Direct Reading Measuring Tools

• Small engines use two types of direct reading
  measuring tools
• Micrometers
• Calipers

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Micrometers
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Micrometer Introduction

• A micrometer is a mechanical device designed to
  measure distances as small as 1/10,000 of an inch
  (0.0001 in).
• Micrometers are only one (1) inch long.
• The micrometer is used with different types and
  sizes of frames to provide precise measurements
  of many different objects.
• Small engines uses three (3) types of
  micrometers
• Micrometer caliper
• Inside micrometer
• Depth gauge micrometer

Micrometer calipers are available in mechanical
and digital models.
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Micrometer Caliper

• A micrometer caliper uses a frame that allows the
  micrometer to measure the thickness of objects.
• For small engine use, different frame sizes are
  used to provide a wider measurement range.
• One inch
• Two inch
• Etc.

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Reading Micrometer Caliper-parts

• The first step in being able to read a micrometer
  is learning the names of the parts.

• The face of the anvil and the face of the spindle
  are the contact surfaces.
• The spindle and thimble turn together.
• The ratchet/friction stop improves the
  repeatability of measurements for beginners.
• A micrometer caliper is read at the point were
  the edge of the thimble crosses the barrel scale

• Insure the lock is released before trying to turn
  the thimble..

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Reading Micrometer Caliper-barrel

• A micrometer caliper is read just like an ruler.
• Start by determining the smallest whole unit, and
  then determine the values of each sub division.
• The smallest whole unit is determined by the
  frame size.
• One (1) inch frame 0.0 smallest whole unit
• Two (2) inch frame 1.0 smallest whole unit.
• Etc.

• The micrometer barrel scale is one (1) inch long
  and is divided into ten (10) sections.
• Each number on the barrel scale 1/10 or 0.1
  inch.

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Reading Micrometer Caliper-barrel

• Each 1/10 of an inch on the barrel scale is
  divided into 4 segments.

• Each short line 0.25 inches (25 thousands of an
  inch).

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Reading Micrometer Caliper-thimble

• The last step is reading the value on the thimble
  scale.
• The thimble scale subdivides the last segment on
  the barrel scale.

• The smallest segment on the barrel is 25
  thousands (0.025).
• The thimble is divided into 25 segments 1/1,000
  or 0.001 inch.

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Micrometer Caliper Example

• Determine the reading for the micrometer caliper
  in the illustration.

• Smallest whole unit 0.000
• Tenths of an inch 0.300
• Twenty five thousands ( 0.025 x 2 ) 0.050
• Thousands 0.015
• Sum (measurement) 0.365

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Micrometer Caliper-digital

• Most measuring tools are available with a digital
  readout.

• Advantages
• Easier to read.
• Can be interfaced with data collection devices
  for automatic recording.
• Easy to convert between English and metric units.

• Disadvantages
• Requires battery
• More expensive

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Inside Micrometer

• Inside micrometers have been replaced by dial
  calipers and other tools for small gas engines.
• The principles for reading are the same.
• The primary difference is determining the
  smallest whole unit.

• The physical size of the micrometer limits the
  smallest whole unit to 1 or 1-1/2 inch.
• Extensions are added to set the minimum size to
  the desired range.

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Inside Micrometer Example

• Read the inside micrometer in the illustration.

Smallest whole unit 1.500 Tenths 0.200 Twenty
Five Thousands 0.025 Thimble 0.014
Sum (reading) 1.734
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Inside Micrometer Example 2

• Inside micrometers use extensions to change the
  range of measurements.
• Adding an extension increases the minimum
  measurement.

In this example a 1/2 inch extension has been
added.
Smallest whole unit 2.000 Tenths 0.200 Twenty
five thousands 0.075 Thousands 0.001
Reading 2.276
Note when the zero on the thimble is close to
the reference line and a 25 thousands line is
close to the edge of the thimble, it may be
difficult to determine if the last line that
should be counted. If the thimble zero is above
the reference line the line is not counted. If
it is below it should be counted.
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Depth Gauge Micrometer

• Depth gauge micrometers are used to measure the
  depth of blind holes, slots, key ways, etc.
• The spindle length can be changed to set the
  micrometer for the desired range of measurement.
• To read a depth gauge micrometer you must
  visualize the distance that has been covered by
  the thimble.

Thimble
Spindle
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Depth Gauge Micrometer Example
Read the depth gauge micrometer in the
illustration

• Smallest whole unit 0.000
• Tenths 0.800
• Twenty Five Thousands 0.050
• Thousands 0.017
• Sum (reading) 0.867

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Calipers
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Introduction

• Calipers can be direct reading or measuring
  transferring tools.
• Direct reading calipers are capable of a wider
  measurement range than micrometer calipers.
• Six (6), eighteen (18) and twenty four (24) inch
  are popular.
• Three common designs of direct reading calipers
• Vernier
• Dial
• Digital

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Vernier Caliper

• Vernier calipers are an old tool that has been
  mostly replaced by dial and digital calipers.
• They are manufactured with decimal scales, metric
  scales and fractional scales.
• The Vernier scale is still used on many
  mechanical measuring tools.

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Vernier Scale

• A Vernier is a mechanical means of magnifying the
  last segment on the main scale so addition
  subdivisions can be made.

• The reference point is the 0 on the vernier
  scale.
• To read a Vernier, the line of coincidence must
  be located.
• The line of coincidence (LOC) is the line on the
  Vernier that coincides with a line on the main
  scale.
• Illustration LOC 19
• In theory only one LOC is possible, but usually
  when reading the vernier it appears several
  exist. When this occurs pick the middle line.

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Vernier Caliper-practice
Read the Vernier caliper in the illustration.
LOC

• Smallest whole unit 1.000
• Tenths of an inch 0.200
• Twenty five thousands 0.000
• Vernier scale 0.011
• Sum
  (measurement) 1.211

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Dial Caliper

• A dial replaces the Vernier.
• This makes the caliper easier to read.
• The reader must still determine the units and
  graduations.

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Measurement Transferring Tools
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Introduction

• Measurement transferring tools are tools that
  collect a measurement, but do not have a scale to
  read the measurement.
• Common tools are
• Spring calipers
• Dividers
• Telescoping gauges
• Ball gauges

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Spring Calipers

• Spring calipers are used to transfer
  measurements.
• Three types of spring calipers
• Outside
• Inside
• Hermaphrodite

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Dividers

• Dividers are very useful for laying out several
  equal distances or transferring a distance
  measurement when other measuring devices cannot
  be used.

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Telescoping gages

• Telescoping gages are used to measure inside
  diameters.
• One or both ends are spring loaded so they can be
  retracted and inserted into the hole being
  measured.
• The measurement is made with a caliper or
  micrometer.

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Ball Gauges

• Ball gauges are use to transfer measurements that
  are too small for telescoping gauges.
• The ball is split and a tapered wedge is used to
  increase and decrease the diameter of the ball
  halves.

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The End