Machining Fundamentals
70
• Wipe gage blocks with a soft cloth or chamois
treated with oil. Be sure the oil is one recom-
mended by the gage manufacturer. See Figure
4-37C.
4.5 DIAL INDICATORS
Industry is constantly searching for ways to
reduce costs without sacrificing quality. Inspection
has always been a costly part of manufacturing. To
speed up this phase of production without sacrific-
ing accuracy, dial indicators and electronic gages are
receiving increased attention.
Dial indicators are designed with shockproof
movements and have jeweled bearings (similar to
fine watches). There are two types of indicators: bal-
anced and continuous. Balanced indicators can take
measurements on either side of a zero line.
Continuous indicators read from “0” in a clockwise
direction. See Figure 4-38.
Dial faces are available in a wide range of
graduations. They usually read in the following
increments:
• 1/1000″ (0.001″)
• 1/100 mm (0.01 mm)
• 1/10,000″ (0.0001″)
• 2/1000 mm (0.002 mm)
Much use is made of dial indicators for center-
ing and aligning work on machine tools, checking
for eccentricity, and visual inspection of work. Dial
indicators must be mounted to rigid holding
devices, Figure 4-39.
A digital electronic indicator, Figure 4-40, fea-
tures direct digital readouts and a traditional grad-
uated dial for fast, accurate reading. These
indicators are available as both self-contained and
remote readout units.
Figure 4-35. A typical set of gage blocks.
(Federal Products Co.)
Federal Accuracy Grades
Tolerance
Accuracy
grade
0.5 AAA
.000001″
.00003 mm
.000002″ .00005 mm
+.000004″ +.0001 mm
–.000002″ –.00005 mm
+.000006″ +.00015 mm
–.000002″ –.00005 mm
AA 1
A + 2
A&B
3
Former
designation
US Conventional
system (inch)
Metric system
(millimeter)
Reference temperature: 68°F (20°C)
One inch = 25.4 millimeters exactly
Figure 4-36. Federal Accuracy Grades for gage blocks.
Figure 4-37. Proper care of gage blocks. A—Handling gage blocks. B—Wipe blocks and slide them together. Do not leave blocks
together for extended periods. C—Wipe blocks with a soft cloth before storing. (Webber Gage Div., L.S. Starrett Co.)
The effect of
temperature
Handle blocks like this
Instead of this
Correct method
of wringing
gages together
Oil-treated
cloth
A
B
C