Yamaha MM700A Manual page 24

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identified with a number. The number sequence depends
on the size of the micrometer. A 0-25 mm micrometer, for
example, has sleeve marks numbered 0 through 25 in 5
mm increments. This numbering sequence continues with
larger micrometers. On all metric micrometers, each mark
on the lower half of the sleeve equals 0.50 mm.
The tapered end of the thimble has fifty lines marked
around it. Each mark equals 0.01 mm. One complete turn
of the thimble aligns its 0 mark with the first line on the
lower half of the sleeve line or 0.50 mm.
When reading a metric micrometer, add the number of
millimeters and half-millimeters on the sleeve line to the
number of one one-hundredth millimeters on the thimble.
Perform the following steps while referring to Figure 33.
1. Read the upper half of the sleeve line and count the
number of lines visible. Each upper line equals 1 mm.
2. See if the half-millimeter line is visible on the lower
sleeve line. If so, add 0.50 to the reading in Step 1.
3. Read the thimble mark that aligns with the sleeve line.
Each thimble mark equals 0.01 mm.
NOTE
Ifa thimble mark does not align exactly with
the sleeve line, estimate the amount between
the lines. For accurate readings in
two-thousandths of a millimeter (0.002
mm), use a metric vernier micrometer.
4. Add the readings from Steps 1-3.
Metric vernier micrometer
A metric vernier micrometer (Figure 34) is accurate to
two-thousandths of a millimeter (0.002 mm). It has the
same markings as a standard metric micrometer with the
addition of a vernier scale on the sleeve. The vernier scale
STANDARD METRIC MICROMETER
Locknut
Anvil
I
\
Ratchet
Thimble marks
consists of five lines marked 0, 2, 4, 6, and 8. These lines
run parallel to the thimble lines and represent 0.002-mm
increments.
When reading a metric vernier micrometer, refer to Fig-
ure 35 and perform the following steps.
1. Read the micrometer in the same way as a standard
metric micrometer. This is the initial reading.
2. If a thimble mark aligns exactly with the sleeve line,
reading the vernier scale is not necessary. If they do not
align, read the vernier scale in Step 3.
3. Determine which vernier scale mark aligns exactly
with one thimble mark. The vernier scale number is the
amount in two-thousandths of a millimeter to add to the
initial reading from Step 1.
Micrometer Adjustment
Before using a micrometer, check its adjustment as fol-
lows.
1. Clean the anvil and spindle faces.
2A. To check a 0-1 in. or 0-25 mm micrometer:
a. Turn the thimble until the spindle contacts the anvil.
If the micrometer has a ratchet stop, use it to ensure
the proper amount of pressure is applied.
b. If the adjustment is correct, the 0 mark on the thim-
ble will align exactly with the 0 mark on the sleeve
line. If the marks do not align, the micrometer is out
of adjustment.
c. Follow the manufacturer's instructions to adjust the
micrometer.
2B. To check a micrometer larger than 1 in. or 25 mm use
the standard gauge supplied by the manufacturer. A stan-
dard gauge is a steel block, disc or rod that is machined to
an exact size.
CHAPTER ONE