Machining Fundamentals
60
tional inch-based micrometer, reading the metric-
based tool will offer no difficulties.
0.353″
Example 3
Add the readings from the sleeve and the thimble:
3 large graduations: 3 0.100 = 0.300
2 small graduations: 2 0.025 = 0.050
3 thimble graduations: 3 0.001 = 0.003
Total mike reading = 0.353″
4.2.3 Reading a Vernier Micrometer
On occasion, it is necessary to measure more
precisely than 0.001″. A Vernier micrometer caliper
is used in these situations. This micrometer has a
third scale around the sleeve that will furnish the
1/10,000″ (0.0001″) reading. See Figure 4-12.
Figure 4-12. A Vernier micrometer caliper includes a Vernier
scale on the sleeve.
The Vernier scale has 11 parallel lines that
occupy the same space as 10 lines on the thimble.
The lines around the sleeve are numbered 1 to 10.
The difference between the spaces on the sleeve and
those on the thimble is one-tenth of a thousandth of
an inch.
To read the Vernier scale, first obtain the thou-
sandths reading, then observe which of the lines on
the Vernier scale coincides (lines up) with a line on
the thimble. Only one of them can line up. If the line
is 1, add 0.0001 to the reading; if line 2, add 0.0002 to
the reading, etc. See Figure 4-13.
4.2.4 Reading a Metric-Based Micrometer
The metric-based micrometer is read as shown
in Figure 4-14. If you are able to read the conven-
0.0002
0.0120
0.2000
0.0750
0.2000
0.0750
0.0120
0.0002
Reading is 0.2872″
Figure 4-13. How to read a Vernier micrometer caliper. Add the
total reading in thousandths, then observe which of the lines on
the Vernier scale coincides with a line on the thimble. In this
case, it is the second line, so 0.0002 is added to the reading.
5.00 mm
0.50 mm
0.28 mm
5.00
0.50
0.28
5.78 mm Reading is
Figure 4-14. To read a metric micrometer, add the total reading
in millimeters visible on the sleeve to the reading of hundredths
of a millimeter, indicated by the graduation on the thimble. Note
that the thimble reading coincides with the longitudinal line on
the micrometer sleeve.
Vernier scale lines