Figure 59. Bathymetry of 3-D Cook Inlet model
Model fabrication
The Cook Inlet 3-D model was carved into Plexiglas using the programmable
router discussed in Chapter 3 and illustrated in Figure 8. Sheets of 2.54-cm-
(1-in.-) thick Plexiglas measuring 1.21 x 2.44 m (4 x 8 ft) were first cut into
smaller pieces measuring 56.64 x 121.9 cm (22.3 x 48 in.), and then three pieces
were laminated together to form a model section with a total thickness of 7.62 cm
(3 in.). The 121.9-cm (48-in.) width was then cut into two pieces and the edges
trimmed up. In other words, the model consisted of 12 blocks measuring
approximately 60.20 x 56.64 cm (23.7 x 22.3 in.) arranged into a 2 x 6 matrix
corresponding to the overall model dimensions. As mentioned earlier, the
primary reason for sectioning the model was to allow different reaches of the
study area to be placed on the flow table. The additional sectioning down the
middle of the long axis of the model was needed for the practical reason of being
able to move the blocks in and out of the flow table as needed without special
hoists. Each block, before carving, weighed about 320.3 N (72 lb), which is
easily maneuvered by two people. Blocks weighed less after the bathymetry was
cut.
A test cut was made into high density Styrofoam to determine the optimum
step-over distance for each traverse of the finish milling bit. A value of about
one one-hundredth of an inch provided smooth results. Next, eight of the
Plexiglas blocks were jigged up on the router table, and a large bit was used to
mill the upper surface of the blocks to perfect level. (There are slight variations
in thickness of the Plexiglas sheets.)
Cutting of the bathymetry for each section proceeded in two steps. First, the
bathymetry was "rough-cut" using a larger bit down to about one-sixteenth inch
above the final elevation. Figure 60 shows the rough-cut on the first section on
the south end of the model. The rough-cut proceeded quickly because the bit
chews out about one-fourth inch of depth with each pass.
77
Chapter 7 Three-Dimensional Cook Inlet Model
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