Basic Measurement 110
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Class Outline
Class Outline
Objectives
The Importance of Measurements
Gaging vs. Inspection
Accuracy and Precision
Sensitivity
The Machinist’s Rule
Calipers
Micrometers
Vernier Scale
Reading a Micrometer
Types of Micrometers
Gage Blocks
Plug Gages
Ring, Thread, and Snap Gages
Optical Comparators
Coordinate Measuring Machines
Instrument Calibration
Summary
Lesson: 1/18
Objectives
l Define standardization.
l Distinguish between gaging and inspection.
l Distinguish between accuracy and precision.
l Define sensitivity for measuring devices.
l Identify the uses for the steel rule.
l Identify the uses for the caliper.
l Identify the uses for the micrometer.
l Explain the vernier scale.
l Read the manual micrometer.
l Identify common micrometers.
l Describe the uses for gage blocks.
l Describe the use of plug gages.
l Identify other common gages.
l Identify the uses for the optical comparator.
l Describe the uses for the coordinate measuring machine.
l Identify the role of calibration.
Figure 1. Most calipers are digital.
Figure 2. Micrometers are common measuring
devices.
Copyright © 2015 Tooling U, LLC. All Rights Reserved.
Lesson: 1/18
Objectives
l Define standardization.
l Distinguish between gaging and inspection.
l Distinguish between accuracy and precision.
l Define sensitivity for measuring devices.
l Identify the uses for the steel rule.
l Identify the uses for the caliper.
l Identify the uses for the micrometer.
l Explain the vernier scale.
l Read the manual micrometer.
l Identify common micrometers.
l Describe the uses for gage blocks.
l Describe the use of plug gages.
l Identify other common gages.
l Identify the uses for the optical comparator.
l Describe the uses for the coordinate measuring machine.
l Identify the role of calibration.
Figure 1. Most calipers are digital.
Figure 2. Micrometers are common measuring
devices.
Lesson: 2/18
The Importance of Measurements
One of the fundamental activities of any manufacturing shop is the measurement of part features.
Individuals in the shop constantly use measuring instruments, such as those in Figure 1, to
compare the actual part to its desired specifications.
The use of measurements is the primary role of inspection, which is the examination of a product
either during or after its creation. In turn, inspection makes it possible to maintain product
standardization. Product standardization is particularly important for parts that must accurately fit
together.
It is easy to forget the importance of standardization. If you buy a light bulb for your lamp or a
blank tape for your video recorder, you assume these products will fit. However, these products fit
because they conform to universally recognized standards. This class will teach you the common
devices used in the shop that make it possible to evaluate whether parts meet their size
requirements.
Copyright © 2015 Tooling U, LLC. All Rights Reserved.
Figure 1. Measuring instruments allow
inspection of part specifications.
Lesson: 2/18
The Importance of Measurements
One of the fundamental activities of any manufacturing shop is the measurement of part features.
Individuals in the shop constantly use measuring instruments, such as those in Figure 1, to
compare the actual part to its desired specifications.
The use of measurements is the primary role of inspection, which is the examination of a product
either during or after its creation. In turn, inspection makes it possible to maintain product
standardization. Product standardization is particularly important for parts that must accurately fit
together.
It is easy to forget the importance of standardization. If you buy a light bulb for your lamp or a
blank tape for your video recorder, you assume these products will fit. However, these products fit
because they conform to universally recognized standards. This class will teach you the common
devices used in the shop that make it possible to evaluate whether parts meet their size
requirements.
Figure 1. Measuring instruments allow
inspection of part specifications.
Lesson: 3/18
Gaging vs. Inspection
Every part feature has a corresponding tolerance, as shown in Figure 1. When you examine a
part, you compare the size of the actual part to an expected measurement. Different devices
perform either gaging or variable inspection.
Gages determine if the measurement falls within the acceptable tolerance range. If you use a gage,
the part either “passes” or “fails” a physical comparison. The measurement is either acceptable or
unacceptable, and there is no in-between.
Likewise, variable inspection tells whether or not a part feature falls within the acceptable tolerance
range. However, inspection also tells how far the actual measurement is from the expected size. An
inspection instrument describes the degree of difference between the part and its blueprint.
A car has gages and instruments. The oil pressure light on your dashboard is a gage. If it turns on, you need more fluid. If it is off, you cannot determine how much fluid you have. The speedometer
is a variable instrument. If you exceed the speed limit, you can compare your actual speed to the
legal limit.
Figure 1. These part features must fall within
an acceptable tolerance range.
Copyright © 2015 Tooling U, LLC. All Rights Reserved.
Lesson: 4/18
Lesson: 3/18
Gaging vs. Inspection
Every part feature has a corresponding tolerance, as shown in Figure 1. When you examine a
part, you compare the size of the actual part to an expected measurement. Different devices
perform either gaging or variable inspection.
Gages determine if the measurement falls within the acceptable tolerance range. If you use a gage,
the part either “passes” or “fails” a physical comparison. The measurement is either acceptable or
unacceptable, and there is no in-between.
Likewise, variable inspection tells whether or not a part feature falls within the acceptable tolerance
range. However, inspection also tells how far the actual measurement is from the expected size. An
inspection instrument describes the degree of difference between the part and its blueprint.
A car has gages and instruments. The oil pressure light on your dashboard is a gage. If it turns on, you need more fluid. If it is off, you cannot determine how much fluid you have. The speedometer
is a variable instrument. If you exceed the speed limit, you can compare your actual speed to the
legal limit.
Figure 1. These part features must fall within
an acceptable tolerance range.
Lesson: 4/18
Accuracy and Precision
Measuring instruments require excellent accuracy and precision. Many people use these words
interchangeably. However, each term describes a different aspect of measurement.
Accuracy describes how close the measurement reading is to the actual true value of that
measurement. Precision is the degree to which the instrument will repeat the same measurement
over time.
Consider the examples in Figure 1. Imagine that a person repeatedly shot at the center of each
target. Target 1 shows a shooter that is accurate but not precise. On average, the shooter is
aimed effectively toward the center. However, the shooter cannot repeat the same location. Target
2 shows a shooter that is precise but inaccurate. The shooter is off-target, but the same location is
easily repeated. Finally, target 3 shows the ideal shooter that is both accurate and precise. The
shots are on-target, and the shooter can easily repeat the process.
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Figure 1. Effective instruments require both
accuracy and precision.
Lesson: 4/18
Accuracy and Precision
Measuring instruments require excellent accuracy and precision. Many people use these words
interchangeably. However, each term describes a different aspect of measurement.
Accuracy describes how close the measurement reading is to the actual true value of that
measurement. Precision is the degree to which the instrument will repeat the same measurement
over time.
Consider the examples in Figure 1. Imagine that a person repeatedly shot at the center of each
target. Target 1 shows a shooter that is accurate but not precise. On average, the shooter is
aimed effectively toward the center. However, the shooter cannot repeat the same location. Target
2 shows a shooter that is precise but inaccurate. The shooter is off-target, but the same location is
easily repeated. Finally, target 3 shows the ideal shooter that is both accurate and precise. The
shots are on-target, and the shooter can easily repeat the process.
Figure 1. Effective instruments require both
accuracy and precision.
Lesson: 5/18
Sensitivity
Measuring instruments can be categorized according to their sensitivity. Every instrument uses
standardized units of measurement, as shown in Figure 1. Sensitivity is the smallest change in
measurement that an instrument can detect. For example, an inexpensive instrument may only be
capable of detecting measurements that are 0.001 in. apart. It would not be sensitive enough to
tell the difference between 1.0002 and 1.0003 in.
Sensitivity is important because it determines the use of the instrument. In order to be effective, a
measuring device must be at least ten times more precise than the required tolerances for the part
measurement. This is called the rule of ten.
For example, the part in Figure 2 has an internal hole with a diameter that must be within 0.005 in.
of the stated dimension. To precisely measure the part, an instrument must be sensitive enough to
detect measurements of 0.0005 in. or smaller.
Figure 1. The bottom instrument has a greater
sensitivity.
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Lesson: 5/18
Sensitivity
Measuring instruments can be categorized according to their sensitivity. Every instrument uses
standardized units of measurement, as shown in Figure 1. Sensitivity is the smallest change in
measurement that an instrument can detect. For example, an inexpensive instrument may only be
capable of detecting measurements that are 0.001 in. apart. It would not be sensitive enough to
tell the difference between 1.0002 and 1.0003 in.
Sensitivity is important because it determines the use of the instrument. In order to be effective, a
measuring device must be at least ten times more precise than the required tolerances for the part
measurement. This is called the rule of ten.
For example, the part in Figure 2 has an internal hole with a diameter that must be within 0.005 in.
of the stated dimension. To precisely measure the part, an instrument must be sensitive enough to
detect measurements of 0.0005 in. or smaller.
Figure 1. The bottom instrument has a greater
sensitivity.
Figure 2. The internal hole must be inspected
with a very sensitive instrument.
Lesson: 6/18
The Machinist’s Rule
Probably the most familiar measuring device is the steel rule, which is shown in Figure 1. You may
also see this device referred to as the machinist’s rule. The steel rule is a metal strip with notches
along the edge that indicate increments of measurement. Most steel rules have English
measurements along one side and metric measurements along the other.
The steel rule is a versatile instrument, and comes in a variety of forms. Most resemble the wooden
rulers you may have used as a young student. Others are available as long tape rules.
Copyright © 2015 Tooling U, LLC. All Rights Reserved.
However, the steel rule is relatively inaccurate. Operators must calculate a measurement by
manually lining up the notches and mentally calculating the length. The greatest sensitivity that a
steel rule offers is 1/64th inch. Consequently, these devices should only be used to measure
Lesson: 6/18
The Machinist’s Rule
Probably the most familiar measuring device is the steel rule, which is shown in Figure 1. You may
also see this device referred to as the machinist’s rule. The steel rule is a metal strip with notches
along the edge that indicate increments of measurement. Most steel rules have English
measurements along one side and metric measurements along the other.
The steel rule is a versatile instrument, and comes in a variety of forms. Most resemble the wooden
rulers you may have used as a young student. Others are available as long tape rules.
However, the steel rule is relatively inaccurate. Operators must calculate a measurement by
manually lining up the notches and mentally calculating the length. The greatest sensitivity that a
steel rule offers is 1/64th inch. Consequently, these devices should only be used to measure
features that are not essential for the proper functioning of a part. For example, a steel rule can be
used to measure stock.
Figure 1. The steel rule uses line markings to
compare measurements.
Lesson: 7/18
Calipers
Another popular measuring instrument is the caliper, which is shown in Figure 1. The caliper has a
long section with measurement markings. On one end, there is a pair of jaws. The outer jaw is
fixed, and the inner jaw slides along the caliper’s beam to indicate the measurement. Most calipers
have two sets of jaws. One pair measures the exterior of parts; the other pair measures the
interior dimensions.
Calipers are versatile because they can measure both outer and inner lengths and diameters, as
well as depth measurements. Figure 2 shows a caliper measuring an internal hole. The range of
most calipers is five inches or more. Most calipers today are sold with a digital readout, which
reduces the chance of miscalculations in the shop.
Though they are more accurate than steel rules, calipers should not be used for precise
measurements. The greatest sensitivity of most digital calipers is 0.001 in. Different operators may
apply different amounts of pressure when taking a measurement. This can create a range of
readings.
Figure 1. Calipers can measure outer
diameters.
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Figure 2. A second pair of jaws can measure
Lesson: 7/18
Calipers
Another popular measuring instrument is the caliper, which is shown in Figure 1. The caliper has a
long section with measurement markings. On one end, there is a pair of jaws. The outer jaw is
fixed, and the inner jaw slides along the caliper’s beam to indicate the measurement. Most calipers
have two sets of jaws. One pair measures the exterior of parts; the other pair measures the
interior dimensions.
Calipers are versatile because they can measure both outer and inner lengths and diameters, as
well as depth measurements. Figure 2 shows a caliper measuring an internal hole. The range of
most calipers is five inches or more. Most calipers today are sold with a digital readout, which
reduces the chance of miscalculations in the shop.
Though they are more accurate than steel rules, calipers should not be used for precise
measurements. The greatest sensitivity of most digital calipers is 0.001 in. Different operators may
apply different amounts of pressure when taking a measurement. This can create a range of
readings.
Figure 1. Calipers can measure outer
diameters.
Figure 2. A second pair of jaws can measure
internal features.
Lesson: 8/18
Micrometers
The most common measuring device in the shop is the micrometer. The micrometer is a U-shaped
device with a threaded spindle on one end and a small anvil on the other. The operator turns the
spindle to gradually advance its end toward the anvil on the opposite side and close in on the part.
The typical micrometer only has a range of one inch, as shown in Figure 1. Consequently, you
would need different micrometers to measure distances between 0 and 1 inches, 1 and 2 inches,
and so on.
A micrometer offers a balance of versatility and accuracy. A regular manual micrometer has a
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2015
Tooling
U, LLC.
All Rights
Reserved.
sensitivity
equals
digital
calipers.
Manual
micrometers with a vernier scale provide sensitivity
to 0.0001 in. Manufacturers also offer digital micrometers. Figure 2 compares these devices. Digital
micrometers can be sensitive to 0.0001 in. and smaller, at least ten times the sensitivity of
Lesson: 8/18
Micrometers
The most common measuring device in the shop is the micrometer. The micrometer is a U-shaped
device with a threaded spindle on one end and a small anvil on the other. The operator turns the
spindle to gradually advance its end toward the anvil on the opposite side and close in on the part.
The typical micrometer only has a range of one inch, as shown in Figure 1. Consequently, you
would need different micrometers to measure distances between 0 and 1 inches, 1 and 2 inches,
and so on.
A micrometer offers a balance of versatility and accuracy. A regular manual micrometer has a
sensitivity that equals digital calipers. Manual micrometers with a vernier scale provide sensitivity
to 0.0001 in. Manufacturers also offer digital micrometers. Figure 2 compares these devices. Digital
micrometers can be sensitive to 0.0001 in. and smaller, at least ten times the sensitivity of
standard manual micrometers.
Figure 1. Each micrometer has a one -inch
range.
Figure 2. Manual and digital micrometers.
Lesson: 9/18
Vernier Scale
Most of the micrometers and calipers you find in the shop will have a digital readout. However, older
dial calipers and manual micrometers may use a vernier scale to yield measurement readings with
greater precision.
A vernier scale consists of two series of lines positioned next to one another. Figure 1 illustrates
this arrangement on a micrometer spindle. The lines in one set are spaced slightly closer together
to each other than the lines in the other set. The operator then examines the scale to see which
pair lines up with each other.
The more closely spaced lines each have a matching number. The number corresponding to the pair
that lines up equips the instrument with a more accurate measurement. Essentially, any manual
instrument with a vernier scale is ten times more sensitive than an instrument without one.
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Figure 1. The "3" lines up on the vernier scale
Lesson: 9/18
Vernier Scale
Most of the micrometers and calipers you find in the shop will have a digital readout. However, older
dial calipers and manual micrometers may use a vernier scale to yield measurement readings with
greater precision.
A vernier scale consists of two series of lines positioned next to one another. Figure 1 illustrates
this arrangement on a micrometer spindle. The lines in one set are spaced slightly closer together
to each other than the lines in the other set. The operator then examines the scale to see which
pair lines up with each other.
The more closely spaced lines each have a matching number. The number corresponding to the pair
that lines up equips the instrument with a more accurate measurement. Essentially, any manual
instrument with a vernier scale is ten times more sensitive than an instrument without one.
Figure 1. The "3" lines up on the vernier scale
of this micrometer.
Lesson: 10/18
Reading a Micrometer
Digital micrometers are very precise and easy to read. However, the reading of a manual micrometer
is still a valuable skill. As you can see in Figure 1, the spindle has markings along the stationary
sleeve and around the revolving thimble. To read a micrometer, simply follow these steps:
1. Note the last visible number along the sleeve. This indicates the value in the tenths position.
2. Note the number of completely visible divisions after the whole number. Each division indicates
0.025 in. after the tenth position.
3. Note the value on the thimble that is at or below the line along the sleeve. This indicates an
additional thousandths position.
4. If the micrometer has a vernier scale, note the line pairing that aligns. This indicates the tenthousandths position.
5. Add the values together to calculate the measurement.
To ensure the greatest possible precision, many micrometers will have a ratchet or similar device
that stops the advance of the spindle after a certain amount of pressure. This prevents the user
from excessively forcing the spindle.
Figure 1. Reading a micrometer involves
adding incrementally smaller values.
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Lesson: 10/18
Reading a Micrometer
Digital micrometers are very precise and easy to read. However, the reading of a manual micrometer
is still a valuable skill. As you can see in Figure 1, the spindle has markings along the stationary
sleeve and around the revolving thimble. To read a micrometer, simply follow these steps:
1. Note the last visible number along the sleeve. This indicates the value in the tenths position.
2. Note the number of completely visible divisions after the whole number. Each division indicates
0.025 in. after the tenth position.
3. Note the value on the thimble that is at or below the line along the sleeve. This indicates an
additional thousandths position.
4. If the micrometer has a vernier scale, note the line pairing that aligns. This indicates the tenthousandths position.
5. Add the values together to calculate the measurement.
To ensure the greatest possible precision, many micrometers will have a ratchet or similar device
that stops the advance of the spindle after a certain amount of pressure. This prevents the user
from excessively forcing the spindle.
Figure 1. Reading a micrometer involves
adding incrementally smaller values.
Lesson: 11/18
Types of Micrometers
Different types of micrometers are available for various measuring needs. The range of a
micrometer is only 1 inch. Consequently, you need a new micrometer to measure a different length
from one inch to the next.
Many types of micrometers are available besides the standard U-shaped device:
l
l
l
The blade micrometer in Figure 1 is used to measure narrow grooves and slots.
The depth micrometer in Figure 2 is used to measure internal depth of holes or slots.
The groove micrometer in Figure 3 is used to measure the widths of internal grooves.
Figure 1. A blade micrometer has flattened
extensions.
Though these devices differ in appearance, they are based on the same principles as the standard
micrometer. In fact, additional micrometers are available for other specialty applications. Different
shapes are necessary to access the features of a wide range of parts.
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Figure 2. A depth micrometer has a thin rod
that extends from the flat base.
Lesson: 11/18
Types of Micrometers
Different types of micrometers are available for various measuring needs. The range of a
micrometer is only 1 inch. Consequently, you need a new micrometer to measure a different length
from one inch to the next.
Many types of micrometers are available besides the standard U-shaped device:
l
l
l
The blade micrometer in Figure 1 is used to measure narrow grooves and slots.
The depth micrometer in Figure 2 is used to measure internal depth of holes or slots.
The groove micrometer in Figure 3 is used to measure the widths of internal grooves.
Figure 1. A blade micrometer has flattened
extensions.
Though these devices differ in appearance, they are based on the same principles as the standard
micrometer. In fact, additional micrometers are available for other specialty applications. Different
shapes are necessary to access the features of a wide range of parts.
Figure 2. A depth micrometer has a thin rod
that extends from the flat base.
Figure 3. A groove micrometer has a small
fixed and moveable disc on the end.
Lesson: 12/18
Gage Blocks
Up to this point, you have learned about instruments that read a specific measurement within a
range. However, manufacturers will also use gaging devices. These devices have a known
measurement, and they indicate whether a part feature is larger or smaller than the specified
measurement.
An essential gaging tool is a set of gage blocks. The standard set consists of 81 metal blocks in
different lengths, as shown in Figure 1. These blocks are available in different grades of accuracy,
as shown in Figure 2. Gage blocks are typically made of heat-treated alloy steel. Carbide gage
blocks are also sold for extra wear resistance.
The surfaces of these blocks are lapped to a mirror finish. This makes it possible to wring gage
blocks together by applying an oil or fluid and twisting the surfaces. By combining gage blocks,
manufacturers can compare practically any measurement.
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Figure 1. A standard set of gage blocks.
Lesson: 12/18
Gage Blocks
Up to this point, you have learned about instruments that read a specific measurement within a
range. However, manufacturers will also use gaging devices. These devices have a known
measurement, and they indicate whether a part feature is larger or smaller than the specified
measurement.
An essential gaging tool is a set of gage blocks. The standard set consists of 81 metal blocks in
different lengths, as shown in Figure 1. These blocks are available in different grades of accuracy,
as shown in Figure 2. Gage blocks are typically made of heat-treated alloy steel. Carbide gage
blocks are also sold for extra wear resistance.
The surfaces of these blocks are lapped to a mirror finish. This makes it possible to wring gage
blocks together by applying an oil or fluid and twisting the surfaces. By combining gage blocks,
manufacturers can compare practically any measurement.
Figure 1. A standard set of gage blocks.
Figure 2. Gage blocks are available in different
accuracy grades.
Lesson: 13/18
Plug Gages
Many parts have round holes, which must be accurate for proper fits. Manufacturers will use plug
gages to quickly check the size of these holes. This process is often called go/no-go gaging.
A plug gage is simply a handheld device with an accurate cylindrical end of a specific diameter.
Figure 1 shows a set of simple plug gages. The plug gage is inserted into the hole to determine if it
fits. Plug gages may have a go and no-go section. These sections may be placed one on each end
as in Figure 2, or the go section will be in front of the no-go section on one end. A hole is the
correct size if the go section enters it but the no-go section does not.
Medium production runs use alloy steel plug gages. For high-production runs, the gages may be
plated with chromium or made with carbide. Most plug gages are round, but tapered and
hexagonal gages are also available.
Figure 1. A set of simple plug gages.
Figure 2. A plug gage with go and no -go
sections on either end.
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Lesson: 13/18
Plug Gages
Many parts have round holes, which must be accurate for proper fits. Manufacturers will use plug
gages to quickly check the size of these holes. This process is often called go/no-go gaging.
A plug gage is simply a handheld device with an accurate cylindrical end of a specific diameter.
Figure 1 shows a set of simple plug gages. The plug gage is inserted into the hole to determine if it
fits. Plug gages may have a go and no-go section. These sections may be placed one on each end
as in Figure 2, or the go section will be in front of the no-go section on one end. A hole is the
correct size if the go section enters it but the no-go section does not.
Medium production runs use alloy steel plug gages. For high-production runs, the gages may be
plated with chromium or made with carbide. Most plug gages are round, but tapered and
hexagonal gages are also available.
Figure 1. A set of simple plug gages.
Figure 2. A plug gage with go and no -go
sections on either end.
Lesson: 14/18
Ring, Thread, and Snap Gages
In addition to plug gages, manufacturers will use these gages to check features of parts:
l
l
l
Ring gages determine the size of cylindrical shafts. They are available in go and no-go pairs.
The no-go ring has a groove around its exterior.
Thread gages check the accuracy of threaded holes. If a hole is accurately threaded, the
gage will travel beyond three turns.
Snap gages measure the size of various external features. They are U-shaped devices with
hardened anvils at each end. The typical snap gage has two adjustable anvils to create go and no-go measurements.
Figure 1 shows both internal and external thread gages. Like plug gages, these devices are made
with alloy steel or wear-resistant carbide. Special gages are also available for checking parts with
more uncommon features.
Figure 1. Thread gages can check both internal
and external threads.
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Lesson: 15/18
Lesson: 14/18
Ring, Thread, and Snap Gages
In addition to plug gages, manufacturers will use these gages to check features of parts:
l
l
l
Ring gages determine the size of cylindrical shafts. They are available in go and no-go pairs.
The no-go ring has a groove around its exterior.
Thread gages check the accuracy of threaded holes. If a hole is accurately threaded, the
gage will travel beyond three turns.
Snap gages measure the size of various external features. They are U-shaped devices with
hardened anvils at each end. The typical snap gage has two adjustable anvils to create go and no-go measurements.
Figure 1 shows both internal and external thread gages. Like plug gages, these devices are made
with alloy steel or wear-resistant carbide. Special gages are also available for checking parts with
more uncommon features.
Figure 1. Thread gages can check both internal
and external threads.
Lesson: 15/18
Optical Comparators
Inspection is becoming increasingly important in the manufacturing world. Companies are
constantly working to manufacture parts with increased precision. However, proper inspection takes
time. Sophisticated measuring devices enable manufacturers to rapidly inspect parts and still
maintain excellent quality.
An example of an efficient measuring instrument is the optical comparator shown in Figure 1. You
may also see this machine referred to as an optical projector. With this machine, the part is placed
on a table, and its magnified image is projected onto a screen. The shape of the part can then be
compared to the contour of a matching drawing.
Optical comparators are very useful because they can quickly check the details of small parts. Most
machines can magnify the image of a part 100 times its normal size or greater.
Figure 1. The optical comparator can inspect
the features of very small parts.
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Lesson: 15/18
Optical Comparators
Inspection is becoming increasingly important in the manufacturing world. Companies are
constantly working to manufacture parts with increased precision. However, proper inspection takes
time. Sophisticated measuring devices enable manufacturers to rapidly inspect parts and still
maintain excellent quality.
An example of an efficient measuring instrument is the optical comparator shown in Figure 1. You
may also see this machine referred to as an optical projector. With this machine, the part is placed
on a table, and its magnified image is projected onto a screen. The shape of the part can then be
compared to the contour of a matching drawing.
Optical comparators are very useful because they can quickly check the details of small parts. Most
machines can magnify the image of a part 100 times its normal size or greater.
Figure 1. The optical comparator can inspect
the features of very small parts.
Lesson: 16/18
Coordinate Measuring Machines
Another example of a sophisticated measuring instrument is the coordinate measuring machine
(CMM), which is shown in Figure 1. The CMM has a large granite table that is finished for excellent
smoothness, with a flatness that stays within 0.0002 to 0.0004 in. over a distance of 30 inches or
more. Above the table, a special probe is suspended. This probe moves vertically and horizontally
along three axes and contacts the part to detect its dimensions. These dimensions are then
recorded on a computer.
The CMM is very useful because it can measure contours very rapidly and accurately. Complex
parts may take several hours to inspect appropriately. A sophisticated CMM can perform the same
task in a few minutes.
Copyright © 2015 Tooling U, LLC. All Rights Reserved.
Lesson: 16/18
Coordinate Measuring Machines
Another example of a sophisticated measuring instrument is the coordinate measuring machine
(CMM), which is shown in Figure 1. The CMM has a large granite table that is finished for excellent
smoothness, with a flatness that stays within 0.0002 to 0.0004 in. over a distance of 30 inches or
more. Above the table, a special probe is suspended. This probe moves vertically and horizontally
along three axes and contacts the part to detect its dimensions. These dimensions are then
recorded on a computer.
The CMM is very useful because it can measure contours very rapidly and accurately. Complex
parts may take several hours to inspect appropriately. A sophisticated CMM can perform the same
task in a few minutes.
Figure 1. The CMM uses a probe to measure
features in three -dimensional space.
Lesson: 17/18
Instrument Calibration
Parts are constantly checked in the shop for accuracy. However, the measuring instruments
themselves must be periodically checked as well. This process is called calibration. Calibration is
the comparison and adjustment of a device with unknown accuracy to a device with a known,
accurate measurement standard to eliminate any variation in the device being checked.
The more often an instrument is used, the greater the frequency of calibration. Commonly used
instruments may need to be calibrated once a year or more. Instruments that are used infrequently
may only need to be calibrated every three or five years. Calibrations are recorded and labeled, as
shown in Figure 1.
In practice, it is better to reject a good part than to declare a bad part within acceptable tolerances.
Consequently, many go plug gages and go ring gages have a certain amount of wear allowance
built into the gage. Wear allowance may add 0.0001 to 0.0006 in. material to the gage. This
prevents the gage from passing a part that is out of tolerance. Calibration corrects for the amount
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© 2015 Tooling
U,time.
LLC. All Rights Reserved.
of
wear experienced
over
Figure 1. The markings on the spindle indicate
the due date for next calibration.
Lesson: 17/18
Instrument Calibration
Parts are constantly checked in the shop for accuracy. However, the measuring instruments
themselves must be periodically checked as well. This process is called calibration. Calibration is
the comparison and adjustment of a device with unknown accuracy to a device with a known,
accurate measurement standard to eliminate any variation in the device being checked.
The more often an instrument is used, the greater the frequency of calibration. Commonly used
instruments may need to be calibrated once a year or more. Instruments that are used infrequently
may only need to be calibrated every three or five years. Calibrations are recorded and labeled, as
shown in Figure 1.
In practice, it is better to reject a good part than to declare a bad part within acceptable tolerances.
Consequently, many go plug gages and go ring gages have a certain amount of wear allowance
built into the gage. Wear allowance may add 0.0001 to 0.0006 in. material to the gage. This
prevents the gage from passing a part that is out of tolerance. Calibration corrects for the amount
of wear experienced over time.
Figure 1. The markings on the spindle indicate
the due date for next calibration.
Lesson: 18/18
Summary
One of the fundamental activities of any shop is the measurement of part features. Consistent
measurement and inspection maintains standardization. Measurements are taken through both
gaging and variable inspection techniques.
Variable inspection takes a specific measurement using common devices such as calipers and
micrometers, as shown in Figure 1. The sensitivity of the instrument must be greater than the
measurement being taken. Both calipers and micrometers are read by finding the alignments in lines
on the devices, as seen in Figure 2. Various micrometers allow for the measurement of certain
features such as depths and grooves.
Gages reveal whether a dimension is acceptable or unacceptable without a specific quantity.
Common gaging devices include gage blocks, plug gages, ring gages, and thread gages. The
go/no-go plug gage in Figure 3 determines whether a hole is acceptable or not.
Figure 1. A dial caliper, depth micrometer, and
digital micrometer.
The optical comparator magnifies a part. It allows for careful inspection of smaller features. The
coordinate measuring machine (CMM) is used to measure part contours too difficult to inspect with
the usual devices.
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Lesson: 18/18
Summary
One of the fundamental activities of any shop is the measurement of part features. Consistent
measurement and inspection maintains standardization. Measurements are taken through both
gaging and variable inspection techniques.
Variable inspection takes a specific measurement using common devices such as calipers and
micrometers, as shown in Figure 1. The sensitivity of the instrument must be greater than the
measurement being taken. Both calipers and micrometers are read by finding the alignments in lines
on the devices, as seen in Figure 2. Various micrometers allow for the measurement of certain
features such as depths and grooves.
Gages reveal whether a dimension is acceptable or unacceptable without a specific quantity.
Common gaging devices include gage blocks, plug gages, ring gages, and thread gages. The
go/no-go plug gage in Figure 3 determines whether a hole is acceptable or not.
Figure 1. A dial caliper, depth micrometer, and
digital micrometer.
The optical comparator magnifies a part. It allows for careful inspection of smaller features. The
coordinate measuring machine (CMM) is used to measure part contours too difficult to inspect with
the usual devices.
Figure 2. The correct micrometer reading is the
total of the marked increments.
Figure 3. A plug gage with go and no -go
sections.
Class Vocabulary
Term
Definition
The
difference between a measurement reading and the true value of that measurement.
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LLC. All Rights
Reserved.
Alloy Steel
Steel that contains added materials that change the property of the metal. Common alloy elements
include chromium, manganese, molybdenum, and nickel.
Class Vocabulary
Term
Definition
Accuracy
Alloy Steel
Axes
Blade Micrometer
Calibration
Caliper
The difference between a measurement reading and the true value of that measurement.
Steel that contains added materials that change the property of the metal. Common alloy elements
include chromium, manganese, molybdenum, and nickel.
Imaginary lines perpendicular to one another that are used to define the position of objects in threedimensional space.
A type of micrometer with flattened tips on the anvil and spindle. It is primarily used to measure narrow
external grooves.
The comparison of a device with unknown accuracy to a device with a known, accurate standard to
eliminate any variation in the device being checked.
A measuring instrument with two pairs of jaws on one end and a long beam containing a marked scale of
unit divisions. One pair of jaws measures external features; the other pair measures internal features.
Carbide
A compound developed by the combination of carbon with usually chromium, tungsten, or titanium.
Carbide materials are very hard and wear resistant.
Chromium
A shiny, hard, steel-gray metal used to add hardness and wear resistance to steel. Many gages are
plated with chromium.
Contour
Coordinate Measuring Machine
Depth Micrometer
English Measurements
Gage Block
Gaging
Go/No-Go Gaging
Granite
Groove Micrometer
Inspection
Lapped
Metric Measurements
Micrometer
A curved surface or feature of a workpiece.
A sophisticated measuring instrument with a flat polished table and a suspended probe that measures
parts in three-dimensional space.
A type of micrometer with a spindle perpendicular to a flat base. It is primarily used to measure the
depth of holes.
A standard system of measurements based on the inch, second, pound, and Fahrenheit degrees.
English measurements are primarily used in the United States and England.
A hardened steel block that is manufactured with highly accurate dimensions. Gage blocks are available in
a set of standardized lengths.
The physical inspection of part features using a device with an established standard size. Gaging results
in a pass/fail decision.
The use of a gage to determine whether a part feature simply passes or fails inspection. No effort is
made to determine the exact degree of error.
A dense, hard type of rock that exhibits excellent wear resistance and stability. Granite tables are used
for various measuring applications.
A type of micrometer with a long stem and two small discs at the end. It is primarily used to measure
the width and position of internal grooves.
The examination of a part during or after its creation to confirm that it adheres to specifications.
Polished with an abrasive paste to remove the last bit of unwanted material.
A standard system of measurements based on the meter, second, kilogram, and Celsius degrees. The
metric system is internationally recognized.
A U-shaped measuring instrument with a threaded spindle that slowly advances toward a small anvil.
Micrometers are available in numerous types for measuring assorted dimensions and features.
Optical Comparator A sophisticated measuring instrument that projects an image of a part onto a screen to compare the
shape,
size, and location of its features.
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Reserved.
Plug Gage
A hardened, cylindrical gage used to inspect the size of a hole. Plug gages are available in standardized
Optical Comparator
Plug Gage
A sophisticated measuring instrument that projects an image of a part onto a screen to compare the
shape, size, and location of its features.
A hardened, cylindrical gage used to inspect the size of a hole. Plug gages are available in standardized
diameters.
Precision
The degree to which an instrument will repeat the same measurement over a period of time.
Ring Gage
A hardened, round gage with a hole used to inspect the size of cylindrical parts or features.
Rule Of Ten
The inspection guideline stating that a measuring instrument must be ten times more precise than the
acceptable tolerance of the inspected part feature.
Sensitivity
The smallest change in a measurement that an instrument is capable of detecting.
Snap Gage
A U-shaped gage with hardened, adjustable anvils on opposite ends used to inspect the length of part
features.
Standardization
Steel Rule
Stock
Thread Gage
Tolerance
Variable Inspection
The development of universally recognized units of measurement. Standardization ensures that parts of
the same size are interchangeable.
A simple measuring instrument consisting of a long, thin metal strip with a marked scale of unit divisions.
Raw material that is used to make manufactured parts. Stock is available in standard shapes such as
long bars, plates, or sheet.
A hardened, threaded gage used to inspect the internal threads of a part.
The unwanted but acceptable deviation from a desired dimension.
The inspection of part features using an instrument calibrated in standard measurement units. Variable
inspection reveals the degree of variation from a given standard.
Vernier Scale
A type of scale consisting of two opposing line markings with different divisions. Vernier scales appear on
both manual calipers and micrometers.
Wear Allowance
The slight amount of material intentionally remaining on a gage to prevent the passing of defective parts
over time.
Wring
To twist and rub together so that the two surfaces cling to one another.
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