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Chapter 1. Basic Machining and Tips
Measurements
How to Use Vernier Callipers
In the machining process, we use vernier callipers or a micrometer for
taking measurements. General analog vernier callipers as shown in Figure
1 can measure with the minimum unit of 1/20 mm. Several types of digital
vernier callipers as shown in Figure 2 can measure with the minimum unit
of 1/100 mm.
Fig. 1, Analog Vernier Callipers
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Fig. 2, Digital Vernier Callipers
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 Examples
The vernier callipers can measure a side length, an outer and inner diameter,
and a depth as shown in Figures 3 to 6.
Fig. 3, Measurement of an Outer Diameter
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Fig. 4, Measurement of a Side Length
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Fig. 5, Measurement of an Inner Diameter
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Fig. 6, Measurement of a Depth
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Keep a perpendicular position in measuring!
The vernier callipers must be kept the perpendicular position in measuring.
Typically, when a beginner measures the size of a complex shaped part,
the result can be inaccurate as the measuring device is often not maintained
parallel to measured piece.
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How to Use a Micrometer
When close tolerances are required, measurements are taken with a micrometer
due to its superior accuracy over a vernier calliper. The micrometer as
shown in Figure 7 can measure with the minimum unit of 1/1000 mm.
Fig. 7, Micrometer
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Fig. 8, Measurement with a Micrometer
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Which do you use the vernier callipers or the micrometer?
The "For & Against" of using micrometers and vernier callipers
are:
Vernier Calliper:
For: A large range of measurements can be made using the one measuring device.
Against: The majority of vernier callipers do not provide sufficient accuracy for close tolerance measurements.
Micrometer:
For: The micrometer provides a greater degree of accuracy for close tolerance work.
Against: Due to the limited size range for a given micrometer, it is necessary to have a number of micrometers to cater for the full range of measurements you may encounter.
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