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TYPES OF GAUGES
Although you can measure any dimension when produced on a component, if
you are working to limits you are only concerned that the work is within those
limits, not its actual size.
Gauging is a method of checking whether work is between the upper and
lower limits and is generally quicker and easier than measuring the exact size.
Gauges are of many different types. This quantum looks at some of these,
together with some gauge design considerations.
Most gap gauges can be designed as adjustable or non-adjustable.
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Non Adjustable
x# cheaper to make
x# no problem setting
accurately as this is done
during manufacture
x# gauge cannot be adjusted
for wear although it could
be re-manufactured to a
larger size
NOT GO
GO
NOT GO
GO
Non adjustable
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Adjustable
x# more expensive to
manufacture
GO
NOT GO
Fixed anvil
x# can be adjusted to cover a
range of sizes therefore
fewer gauges will be needed
x# wear will be automatically
compensated for as gauge is
reset
x# heavier
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Adjustable
Adjustable
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RING GAUGES
Ring gauges are fixed size gauges
generally used where
concentricity/roundness is important
as this is not checked by a gap gauge.
PLUG GAUGES
GO
Plug gauges may be solid or
renewable as shown.
NOT GO
Solid
Plastic handle
GO
Renewable
NOT GO
Knock out hole
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THREAD GAUGES
For Internal Thread
GO gauge is full form made to low limits of size. The gauging length is equal to
work length of engagement.
Work
GO Gauge
NOT GO gauge for effective diameter made to high limit with restricted contact
with work threads and length of 2 or 3 thread forms.
Work
NOT GO
Gauge
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NOT GO gauge for minor diameter is a cylindrical plug gauge made to high
limit of minor diameter.
Work
NOT GO Gauge for
minor diameter
For External Thread
GO gauge is full form of caliper/gap type and is made to high limits of size.
GO Gauge
Work
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NOT GO for effective diameter is made to low limits and has restricted contact.
Gauge is of caliper/gap type.
NOT GO
Work
NOT GO for major diameter is a plain caliper or gap gauge made to low limit of
major diameter.
NOT GO
Work
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In many cases gauges for external threads are of the combined GO and NOT
GO type as shown below. The anvil form will be as shown previously.
GO
GO
NOT
GO
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NOT
GO
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OTHER TYPES OF GAUGE
DEPTH/THUMB NAIL
Hole depth within
permissible limits
End of gauge
below collar
Gauge step
above collar
Work
Hole too
deep
Work
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Hole too
shallow
Work
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STEP
NOT
GO
GO
Dimension
being
checked
SWING
NOT
GO
Dimension
being
checked
NOT GO will catch
bottom of slot/hole
when swung
GO
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TAPER
Top surface of work between
two levels on gauge
Work
Work correct
Work oversize
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Work undersize
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GAUGE MAKER'S TOLERANCE AND WEAR ON GAUGES
For non adjustable gauges some account must be taken of the expected wear
which will eventually lead to the gauge becoming unusable.
BS 969 allows for wear on gauges made for work with tolerance zones greater
than 0.09 mm.
Wear allowance will only be necessary on GO gauges as NOT GO gauges will
not normally enter or pass over work so wear will not take place.
Just as you need a tolerance on any work you do, the gauge maker needs a
tolerance on the gauge. Although the gauge will be made to much higher
standards of accuracy it will still not be exact and limits will be necessary.
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A general rule is that the gauge tolerance will be 1/10th of the work tolerance,
though BS 969 gives much greater detail. To allow the wear to make the
gauge more correct, the tolerance zones are positioned as shown.
PLUG GAUGES
Gauge tolerance
Upper limit
Upper limit
Gauge
tolerance
the tolerance zone falls within the tolerance zone of the
component.
Low limit
–
Low limit
GO Gauge
Gauge
Work
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NOT GO Gauge
– the tolerance zone falls outside the tolerance zone of
the component.
Upper limit
Low limit
Gauge
tolerance
Gauge
Work
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RING AND GAP GAUGES
high limit of gauge size is the high limit of work.
Low limit
Upper limit
Work
tolerance
Gauge
tolerance
Work
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Upper limit
–
Low limit
GO Gauge
GO
Gauge
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NOT GO Gauge
– the high limit of the gauge size is equal to the low limit
of the work.
Work
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NOT GO
gauge
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Self Assessment
Select the correct answer to the following questions by typing the
letter a, b, c or d in the box provided.
1
Gauges:
a
measure work accurately
b
are suitable when working to limits
c
are not acceptable for accurate work
d
cannot be used for inspecting work
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2
Non adjustable gap gauges are:
a
cheaper than adjustable ones
b
heavier than adjustable ones
c
not subject to wear on the GO faces
d
more expensive than adjustable gauges
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3
Ring gauges:
a
only check a diameter at two opposite points
b
are only suitable for checking internal dimensions
c
check roundness as well as size
d
have renewable gauging surfaces
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4
Plug gauges:
a
are only used for thread gauging
b
may be solid or renewable
c
are completely made of metal
d
have the NOT GO member longer than the GO member
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5
Gauges:
a
do not need a tolerance as they are very accurate
b
are designed to wear away from its correct size
c
have a tolerance on size which is half the work
tolerance
d
are designed to wear towards the correct size
Click here to check your answers
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Assignment
PRACTICAL MEASUREMENT
Your tutor will make available a set of machined specimens, the associated
drawings and suitable measuring equipment.
Click here to print out the drawings
Choose the most appropriate measuring instruments to check each of the
toleranced dimensions. Indicate in the table on the following screen, whether
they are correct, or incorrect, to the drawings by placing a tick in the
appropriate box. Also indicate the equipment used.
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Specimen
no
Correct
to drg.
Incorrect
to drg.
Equipment used
1
2
3
4
5
6
After use clean and grease the equipment, if necessary, and return to its
appropriate box or storage.
Click here to check your answers
Click the Home Button to move on
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REVIEW PACK – SELF ASSESSMENT
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1
b
2
a
3
c
4
b
5
d
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REVIEW PACK – ASSIGNMENT – PRACTICAL MEASUREMENT
Specimen
no
Correct
to drg.
9
1
2
Incorrect
to drg.
9
Slips and D.T.I.
Sine bar and slips
9
3
Equipment used
Sine centre and slips
4
9
Micrometer
5
9
Plug gauge
6
9
Slips
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