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David Merriman's 57" Seaview part 2 |
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The Radar Antenna
The radar antenna itself was a laboriously cut out piece of twenty-pound Model Builder's foam.
Man...! That item took me days to complete with sharp knife, jeweler's files, and magnifying glasses. I could only stand to work on this little piece for ten-minutes at a time before the urge to kill something
overcame me! That job started by cutting out a blank of the antenna, plotting the slot openings on the blank, drilling holes to start the slots, and then working with new #11 X-acto blades until the desired shape
had been achieved - what a nightmare job!
The entire radar antenna unit consisted of three parts: the mast, which was turned from machine brass rod; the previously discussed antenna; and the signal 'horn',
cut from a piece of brass sheet. The horn and mast were soldered together and a groove was cut into the base of the antenna to slip it over an extension of the horn. CA adhesive was used to secure (rather flimsily)
the antenna to the mast. What the master lacked in strength at the antenna/mast interface point would become a very stout connection on the later produced cast white metal radar antenna part.
The Hatches
Of course the lathe work only achieved the disc portions of each hatch master. To make the two gussets that ran from the backside of each hatch (the gussets terminated at the
rear of each hatch with an interconnecting hatch counter-weight spring), I cut two slits through each hatch disc and soldered a piece of brass sheet within each slit. The brass gussets were filed down till the
correct shape had been achieved, and the counter-weight spring inserted between them.
Sounds simple enough, but these things are SMALL! Eye strain city!
To represent the coiled springs I wound
annealed small gauge brass wire around the shank end of a very small drill bit (the high speed steel from which most drill bits are cut is very difficult to solder, so a drill bit is usually a good mandrel choice
for this type work). A small dab of solder, proceeded by some acid flux, is applied to this 'spring', holding it from uncoiling or bending when the work is slid off the drill shank. Excess solder was removed with a
'wick' to retain the sharp relief of the helically wound wire. As a spring was soldered up, it was pulled off the drill shank and cut making it a tight friction fit between the hatch gussets, then it was soldered in
place.
Pre-existing masters that were pulled from storage were the 'football antenna' (from masters I produced in support of our 1/96 SKIPJACK kit), and the two bell cranks (from a 1/96 SEAWOLF submarine kit).
The two bell cranks are practical items on the model. They connect to the internal operating shafts of the stern planes and skeg rudder. These bell cranks make up to push rods that in turn run through water
tight seals and on to the servos mounted within the WTC-3 mod 2 (internal water tight cylinder).
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Funny thing, but the SEAVIEW periscope, antenna, and football masts are not equipped with streamlined fairings as is the practice on modern
American submarines. OK, that made my life easier. Another oddity: there are no indications on the studio drawings or photos of the studio miniatures of any recesses in the top of the sail to accommodate the
retracted football antenna. Hmmm...
After building up the hatches and assembling the radar pieces into a single unit, all metal items (including the scopes and binnacle) were 'pickled' in Ferric Chloride acid
briefly and then rinsed in soapy water to kill the acid, then a fresh water rinse to remove the soap, then dried. This etching of the metals surface affords it good mechanical tooth, which permits very tight 'grab'
of the primer.
All masters were then given a heavy spray coat of DuPont Lucite brand, 131S acrylic lacquer, gray primer.
After the primer dried, the hatches were detailed further with small bits of
styrene sheet to represent hatch 'dogs', deck gussets, and bearings. The binnacle received a small square piece of sheet to represent a fuse/dimmer switch/junction box mounted on the side of the pedestal, just under
the housing representing the gyrocompass repeater. After a little putty touch up to the antenna assembly and binnacle junction box, all masters were primed again, readying them for manufacture of the spin-casting
'disc' type rubber tool.
METAL CASTING
The disc type spin-casting tool is unique in that the cavities of the tool are arrayed around the center. The disc tool, designed to spin at high RPM, is subject
to a great deal of centrifugal force - this force increases as the square of the distance from the center of rotation. The sprue hole, the point where molten metal is introduced into the tool, at the tools center of
rotation. The molten metal is introduced as the tool spins.
Incidentally, you can spin cast either resin or metal using the same tool.
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Making The Spin Casting Tool
In preparation of making the first half of the disc tool, the masters were set about
half-way into a clay backing. A brass tube was stood up in the center of the clay disc. Around the tube, arrayed wagon-wheel fashion sat the masters. The tube, of course, later produced in the rubber tool the sprue
hole through which molten metal would be introduced to the tool cavities. Note the many small depressions set into the clay. These depressions form the positive (and later, within the other tool half, the negative)
interlocking 'keys' needed to assure exact registration between the two tool halves when assembled.
The first batch of RTV was mixed and poured over the masters. After this cured hard, the work was flipped,
the clay backing removed, the master pulled out, cleaned up, and a mold release applied to the face of the first tool half. Then the masters were reinstalled, a second batch of RTV mixed and poured to create the
second half of the two piece disc tool.
Onto more of part 2
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