Chapter 4 Measurement
73
enlarged image of the part is projected upon a
screen for inspection. The part image is superim-
posed upon an enlarged, accurate drawing of the
correct shape and size. The comparison is made
visually. Variations as small as 0.0005″ (0.012 mm)
can be noted by a skilled operator.
4.6.5 Optical Flats
Optical flats are precise measuring instruments
that use light waves as a measuring standard,
Figure 4-46. The flats are made of quartz and have
one face ground and polished to optical flatness.
When this face is placed on a machined surface and
a special light passed through it, light bands appear
on the surface, Figure 4-47. The shape of these
bands indicate to the inspector the accuracy of the
part. See Figure 4-48.
Figure 4-43. This electronic bore gaging system can deliver
electronic resolution as fine as 0.00001″ (0.0002 mm). Using
replaceable gaging probes, the self-contained unit measures
diameters ranging from 0.370″ to 2.900″. It also measures in
millimeters. It can be linked to a computer for statistical process
control (SPC) data collection. (Sunnen Products Company)
Figure 4-44. This laser is being used to inspect a part from a
car’s automatic transmission. Manually, one person could
inspect no more than four units an hour. The laser can inspect
over 120 parts an hour. (Ford Motor Co.)
Figure 4-45. This 50-power optical comparator permits a fast
check of the tooth formation on a tap.
Figure 4-46. Optical flats are used for precision flatness,
parallelism, size, and surface variations. (L. S. Starrett Co.)