Yamaha MM700A Manual page 20

14
Calipers
Calipers (Figure 25) are excellent tools for obtaining
inside, outside and depth measurements. Although not as
precise as a micrometer, they allow reasonable precision,
typically to within 0.05 mm (0.001 in.). Most calipers
have a range up to 150 mm (6 in.).
Calipers are available in dial, vernier or digital versions.
Dial calipers have a dial readout that provides convenient
reading. Vernier calipers have marked scales that must be
compared to determine the measurement. The digital cali-
per uses an LCD to show the measurement.
Properly maintain the measuring surfaces of the caliper.
There must not be any dirt or burrs between the tool and
the object being measured. Never force the caliper closed
around an object: close the caliper around the highest
point so it can be removed with a slight drag. Some cali-
pers require calibration. Always refer to the manufac-
turer's instructions when using a new or unfamiliar
caliper.
To read a vernier caliper refer to Figure 26. The fixed
scale is marked in 1 mm increments. Ten individual lines
on the fixed scale equal 1 cm. The movable scale is
marked in 0.05 mm (hundredth) increments. To obtain a
reading, establish the first number by the location of the 0
line on the movable scale in relation to the first line to the
left on the fixed scale. In this example, the number is 10
mm. To determine the next number, note which of the
lines on the movable scale align with a mark on the fixed
scale. A number of lines will seem close, but only one will
align exactly. In this case, 0.50 mm is the reading to add to
the first number. The result of adding 10 mm and 0.50 mm
is a measurement of 10.50 mm.
Micrometers
A micrometer (Figure 27) is an instrument designed for
linear measurement using the decimal divisions of the
inch or meter. While there are many types and styles of
micrometers, most of the procedures in this manual call
for an outside micrometer. The outside micrometer is used
to measure the outside diameter of cylindrical forms and
the thickness of materials.
A micrometer's size indicates the minimum and maxi-
mum size of a part that it can measure. The usual sizes
(Figure 27) are 0-1 in. (0-25 mm), 1-2 in. (25-50 mm), 2-3
in. (50-75 mm) and 3-4 in. (75-100 mm).
Micrometers that cover a wider range of measurement
are available. These use a large frame with interchange-
able anvils of various lengths. This type of micrometer of-
fers a cost savings; however, its overall size may make it
less convenient.
Reading a Micrometer
When reading a micrometer, numbers are taken from
different scales and added together. The following sec-
tions describe how to read the measurements of various
types of outside micrometers.
For accurate results, properly maintain the measuring
surfaces of the micrometer. There cannot be any dirt or
burrs between the tool and the measured object. Never
force the micrometer closed around an object. Close the
micrometer around the highest point so it can he removed
with a slight drag. Figure 28 shows the markings and
parts of a standard inch micrometer. Be familiar with
these terms before using a micrometer in the follow sec-
tions.
Standard inch micrometer
The standard inch micrometer is accurate to
one-thousandth of an inch or 0.001. The sleeve is marked
in 0.025 in. increments. Every fourth sleeve mark is num-
bered 1,2,3,4,5,6,7,8,9. These numbers indicate 0.100
in., 0.200 in., 0.300 in., and so on.
The tapered end of the thimble has twenty-five lines
marked around it. Each mark equals 0.001 in. One com-
plete turn of the thimble will align its zero mark with the
first mark on the sleeve or 0.025 in.
When reading a standard inch micrometer, perform the
following steps while referring to Figure 29.
1. Read the sleeve and find the largest number visible.
Each sleeve number equals 0.100 in.
2. Count the number of lines between the numbered
sleeve mark and the edge of the thimble. Each sleeve mark
equals 0.025 in.
3. Read the thimble mark that aligns with the sleeve line.
Each thimble mark equals 0.001 in.
CHAPTER ONE