Tweet
A Report to the Cabal: WRITTEN BY DAVID MERRIMAN
The long delayed release of the Caswell-Palumbo-Merriman 1/72 FOXTROT kit is mostly my fault. I became involved in other, pressing jobs that I unwisely crowded onto the schedule.
My major FOXTROT responsibility has been the creation of fittings packages that will accompany the hull and sail pieces produced by Rick Palumbo, a Model Builder of exceptional skill. My fittings kit to contain internal fittings, control surfaces, masts and antennas, bridge structures, zincs, deck fittings, anchor and anchor well, and propellers and dunce-caps.
Most of those masters are completed and have already been used to make tools, and from those tools I've cast up a box full of model parts. Now, in the final strokes of this job, I'm completing work on some of the most demanding masters: the antennas, scopes, and mast stuffing tubes -- once that work is done, I'm done.
In this installment of the Cabal Report here's a look at the work being done on the Electronics Counter Measure (ECM) antenna -- a master principally constructed of dense RenShape, turned on a lathe, faceted, and studded with stretched-sprue derived 'antenna nubs'.
RenShape is wonderful stuff. I've been using it well over a decade now -- I have completely abandoned the use of wood as a model building medium since I discovered RenShape. RenShape is the perfect substitute for wood, MDF, and other foamed construction materials.
http://www.freemansupply.com/RenShapeToolingand.htm
Almost all structures I manufacture, be they a master or the finished model part, are now fabricated from RenShape Pattern Maker's medium. This is a dense foam material that is graded by density -- the heavier the RenShape, the tighter the cellular structure of the foam. The forty-pound. (per cubic foot) material are contained in the boxes center and left. The light-weight, twenty-pound stuff is in the box to the right.
Dense RenShape produces a surface ready for primer, but is harder to work. The light-weight RenShape cuts like butter but produces a course surface finish that requires filling before you can move on to primer.
My low-speed lathe (built from a discarded variable-speed drill motor), with an indexing plate screwed to the face of its chuck, was used to turn to shape and index the ECM master as I cut in equally spaced, longitudinal engraved lines. I use this machine for radial and longitudinal lay-out and machining work to the smaller sized cylindrical masters and parts.
Note that the indexing plate is marked to indicate any number of equally spaced points about a circle.
Here I'm defining the spacing of the facets along the surface of the ECM master -- making good use of the machines mounted indexing plate to achieve that spacing with remarkably symmetry.
As the machines chuck is rotated 1/8 turn, a scribe is pulled along the tool rest and its point into the work, cutting a longitudinal engraved line. Eight equally space lines are so cut to denote the longitudinal edge of the facets over which the ECM's antenna nubs will later project. The gray unit I'm holding to the side was a test/evaluation ECM made to explore some fabrication methods I wanted to get straight before committing those techniques to the actual ECM master.
Once the longitudinal engraved lines were cut onto the ECM master, I then rotated the work on the little lathe and laid down radial pencil lines, denoting the height of the four rows of antenna nubs that will eventually be glued into holes drilled into the master to receive them. After marking, I pulled the master off the machine and punched in pilot holes with the tip of my scribing tool (a modified rat-tail jeweler's file).
Once the pilot holes had been punched into the ECM master I used a pin-vice, holding a .020" drill bit, and drilled holes into the master to accept the tiny antenna nubs. But, before that I had to produce the flat faces of the facets. Back to the little lathe the master went ...
... Before gluing on the antenna nubs I chucked the master back onto the machine and filed flat the facets under which the nubs would be glued. That facing initially done with a jeweler's file, followed up with a sanding stick.
Deepening engraved lines between antenna nub facets.
Small model parts don't throw shadows like their big prototypes. So, such things as engraved lines and high-profile areas on the model representation are exaggerated in order to display darker shadows under relatively subdued lighting conditions. Remember, most of the visualization we get from a prototype is under direct sunlight -- when we view the model representation of that prototype, viewing is done under low-intensity, much diffused light. Hence, the need to cheat by over deepening engraved lines and application of washes and counter-shading; model make-up, if you will.
A basic but still useful model building technique: Stretching sprue to small cross section rods.
Stretched-sprue was used on this job as the raw material from which the tiny antenna nubs would be fashioned. I took advantage of the polystyrenes thermoplastic characteristics: first, to alter the diameter of the sprue through stretching; and later, by directed heat to the end of the small diameter sprue pieces, to produce little nubs of the approximate diameter and height required.
Final shaping of the antenna nubs was accomplished after they were affixed to the ECM structure -- that work done with special tube cutters that were hand-twisted over the nubs to get them to correct diameter.
Lengths of stretched sprue were heated with a soldering iron tip, at one end, to produce the nubs you see here, ready to be glued into the holes of the ECM master. Initially I used white-glue to hold these nubs in the holes -- the slow-drying glue permitted moving the nubs around to get them centered within their respective facets. Once the white-glue had set hard I coated the entire assembly with thin CA to permanently secure the nubs in place onto the ECM structure.
It's my practice to study my documentation and to then make sketches of the required sub-assemblies, in order to explore optional ways of manufacture of the part/master -- eventually settling on the easiest, strongest, and most faithful to the look of the prototype method. Example here is a drawing for the 1/72 FOXTROT's radar and ECM antennas. I've placed the masters next to the illustrations I made months ago.
Nearly completed ECM, DF loop, and radar antenna masters over a photo of those antennas seen on a museum boat of the FOXTROT class. A significant amount of my energies directed at the FOXTROT fittings kit have been invested in these three parts!
Once the ECM and other master are completed and tools made, I will add cast resin and cast metal parts of those items to the FOXTROT fittings kits I'm desperately trying to complete and get out to Mr. Caswell for distribution to his long-suffering customers.
Comment