Without some form of accurate measurement,
modern industry could not exist. The science that
deals with systems of measurement is called
metrology. Today, industry can make measurements
accurate to one microinch (one-millionth of an inch).
If a microinch were as thick as a dime, one inch
would be as high as four Empire State Buildings
(about 5000′ total). An engineer once estimated,
with tongue in cheek, that a steel railroad rail sup-
ported at both ends would sag one-millionth of an
inch when a “fat horsefly” landed on it in the
middle.
In addition to using US Conventional units of
measure (inch, foot, etc.), industry is gradually
converting to metric units of measure (millimeter,
meter, etc.), called the International System of
Units (abbreviated SI). A micrometer is one-
millionth of a meter (0.000001 m).
All of the familiar measuring tools are available
with scales graduated in metric units, Figure 4-1. An
SI Metric (millimeter) rule is compared with con-
ventional fractional and decimal rules in Figure 4-2.
Metric-based measuring tools should offer no prob-
lems for the user. As a matter of fact, they are often
easier to read than inch-based measuring tools.
Although you will measure in very tiny units
when you go to work in industry, you must first
learn to read a rule to 1/64″ and 0.5 mm. Then,
you can progress through 1/1000″ (0.001″) and
1/100 mm (0.01 mm) by learning to use micrometer
and Vernier-type measuring tools. Finally, you
can progress to 1/10,000″ (0.0001″) and 1/500 mm
(0.002 mm) by using the Vernier scale on some
micrometers.
55
Chapter
4
Measurement
LEARNING OBJECTIVES
After studying this chapter, you will be able to:
Measure to 1/64″ (0.5 mm) with a steel rule.
Measure to 0.0001″ (0.002 mm) using a
Vernier micrometer caliper.
Measure to 0.001″ (0.02 mm) using Vernier
measuring tools.
Measure angles to 0°5′ using a universal
Vernier bevel.
Identify and use various types of gages
found in a machine shop.
Use a dial indicator.
Employ the various helper measuring tools
found in a machine shop.
IMPORTANT TERMS
dial indicators
gage blocks
gaging
graduations
helper measuring tools
International System of
Units
metrology
micrometer caliper
steel rule
Vernier caliper
Figure 4-1. This rule can be used to make measurements in
both US Conventional and SI Metric units.
4.1 THE RULE
The steel rule, often incorrectly called a scale, is
the simplest of the measuring tools found in the
shop. Figure 4-2 shows the three basic types of rule
graduations. A few of the many rule styles are
shown in Figure 4-3.