I needed twelve little tear-drop shaped items to fasten to the forward end of the hull, just a few scale feet below the waterline. These would represent the anti-corrosion zinc anodes along the all-steel portions of the Type-212's hull. The after portion of the submarines hull is presumably GRP -- the pressure hull stepping radically down in diameter aft of the sail, making room in the annular space between after pressure hull and GRP outer hull for the many cryogenic pressure bottles associated with the submarines Air Independent Propulsion (AIP) machinery.
You can see these external zincs in the two pictures of actual Type-212 boats below. There are six of these zincs on each side of the hull. My problem was how to fabricate these little critters quickly, with assured uniformity of form between them, and from a material that was quick curing and also easy to work with. The answer was to use the same Alumilite polyurethane two-part casting resin I used for the larger castings. However, the tools used to give shape to these zinc parts would be a simple, one-shot, open face clay mold.
The completed model show off the little zincs, CA'ed in place. Items as small as these tear-drop shaped resin zincs are best handled with tweezers and/or the tip of a sharp #11 X-Acto blade. Though I was tempted to leave these little detail items off the model, I found that their inclusion greatly enhanced the 'busy' aspects of the subject.
Here is a shot of the in-mass grouping of the Type-212 tear-drop shaped zincs. The thin connecting film is an artifact of the casting process. Removing the individual zincs from this fret was done by sliding the fret over a piece of #400 sandpaper till the film was worn away, leaving the individual zinc parts, ready for final sanding, priming, and installation to the Type-212's hull. The Mold was formed from oil-clay that had been rolled out flat on a moldboard and the tear-drop cavities formed with a piece of plastic square-section rod that had one end cut and sanded to the desired shape. To one side of this form I glued a depth-stop -- it's job to insure that all cavities pressed into the clay were of uniform depth.
Once all the cavities had been pushed into the clay, I sprayed on some Mann 200 silicon mold-release spray; mixed up a small amount of casting resin, poured it over the clay; then laid down a piece of wax-paper. Capillary action pulled the wax-paper down tight onto the surface of the clay, minimizing the thickness of the resin film that formed over what would become the base of the little zinc parts. Once cured the cast fret of zincs was pulled away from the clay, dunked in a container of lacquer thinner and scrubbed with a stiff brush to get rid of any clinging mold-release.
Each zinc was painted primer gray. Then, using the drawing of the Type-212, I plotted the longitudinal location of each zincs onto a length of masking tape. Using that tape as a guide I CA'ed each zinc in place on the hull
You can see these external zincs in the two pictures of actual Type-212 boats below. There are six of these zincs on each side of the hull. My problem was how to fabricate these little critters quickly, with assured uniformity of form between them, and from a material that was quick curing and also easy to work with. The answer was to use the same Alumilite polyurethane two-part casting resin I used for the larger castings. However, the tools used to give shape to these zinc parts would be a simple, one-shot, open face clay mold.
The completed model show off the little zincs, CA'ed in place. Items as small as these tear-drop shaped resin zincs are best handled with tweezers and/or the tip of a sharp #11 X-Acto blade. Though I was tempted to leave these little detail items off the model, I found that their inclusion greatly enhanced the 'busy' aspects of the subject.
Here is a shot of the in-mass grouping of the Type-212 tear-drop shaped zincs. The thin connecting film is an artifact of the casting process. Removing the individual zincs from this fret was done by sliding the fret over a piece of #400 sandpaper till the film was worn away, leaving the individual zinc parts, ready for final sanding, priming, and installation to the Type-212's hull. The Mold was formed from oil-clay that had been rolled out flat on a moldboard and the tear-drop cavities formed with a piece of plastic square-section rod that had one end cut and sanded to the desired shape. To one side of this form I glued a depth-stop -- it's job to insure that all cavities pressed into the clay were of uniform depth.
Once all the cavities had been pushed into the clay, I sprayed on some Mann 200 silicon mold-release spray; mixed up a small amount of casting resin, poured it over the clay; then laid down a piece of wax-paper. Capillary action pulled the wax-paper down tight onto the surface of the clay, minimizing the thickness of the resin film that formed over what would become the base of the little zinc parts. Once cured the cast fret of zincs was pulled away from the clay, dunked in a container of lacquer thinner and scrubbed with a stiff brush to get rid of any clinging mold-release.
Each zinc was painted primer gray. Then, using the drawing of the Type-212, I plotted the longitudinal location of each zincs onto a length of masking tape. Using that tape as a guide I CA'ed each zinc in place on the hull
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