Upgrading the 1/100 OTW VANGUARD Kit, Part-7

A Report to the Cabal:

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Now, for the resin and metal casting operations ... finally! Time to produce the parts needed to upgrade the 1/100 OTW VANGUARD model. We'll take a glance at the procedures and tools used to resin cast with vacuum, pressure, and centrifugal assist. And a quick look at how I use the same centrifuge to cast white metal rotors.

At last, payoff for all the master and tooling work! Enjoy.

I'm jumping ahead here to show the endgame to all the preceding horse-shit; the reason why I did the research, made the working drawings, built the masters, formed the tools, and cast the resin and metal part: New appendages for the OTW 1/100 scale VANGUARD kit.

Here I'm showing off a set of cast resin enhancement parts temporarily secured to the GRP VANGUARD hull. A transverse operating shaft interconnects the two bow planes, later that shaft will be outfitted with a bell-crank to translate linear motion from the WTC's pushrod to radial motion of the planes. The sail connects atop the sail with two 6-32 machine screws. The sail platforms (two of them) are rafted below the top sail piece with two long 4-40 machine screws. Just for fun I've inserted fairing masters and lengths of suitable diameter aluminum tube to check out fit and alignment of the retractable items within their foundation pieces within the sail -- perfect!

Here are the major tools outfitted with strongbacks of one form or another -- except the propeller tool in foreground, that is secured to a special clamping device once set on the bed of the centrifuge. This, pretty much, is the condition of the tools when resin or metal is introduced into them.

Though a simple two-piece rubber tool, this mold required a two-stage casting process: first, just after pouring the resin into the wide 'trench' type sprue opening, the tool was placed into a vacuum chamber, the air evacuated, the entrapped bubbles within the very thin cavities (representing the top of the sail and the two internal mast foundation platforms) enlarging to a froth which was evacuated out the pump, the vacuum quickly busted, the tool then transferred to a pressure pot where it was then subjected to a two-atmosphere overpressure to dissolve any remaining bubbles in the cavities. All this must happen within ninety-seconds -- the pot life of the Alumilite 'standard' tan resin.

Rose's left thumb is sticking in the frothing trench of the tool.

To the left is the sail top assembly. The two platforms beneath it secure the many masts that project through the openings in the top of the sail perpendicular to the boats longitudinal centerline. The whole affair is held together with two 4-40 machine screws. During the casting operation two of these screws are inserted into the tool, giving form to threaded holes in the foundations within the sail top and lower foundation platform.

All this work done so that the observer would see a scalelike thickness at the edges of the many holes that penetrate the top of the sail -- that necessity of scale required this rather involved means of securing the masts within the sail. But, I think you'll agree, the presentation looks 'realistic.'

Rubber tools designed for vacuum assisted resin casting require long, horizontal fill channels connecting to the cavities and a deep 'frothing trench' to contain the bubbling mass of resin that issues forth the moment you evacuate the air. This process is the only way to achieve perfect, bubble free casting of parts that posses thin walls and are small of form.

I learned this casting technique at an IPMS Nationals years ago -- I asked this fat guy how he produced flawless after-market jet engine 'turkey' feather' resin castings (items of paper thin section at the end of the nozzles) that he was marketing. I was simply stunned at the confidence of this guy; he had absolutely no qualms about sharing his vast wealth of model building experience and refined techniques. In ten minutes I learned so much about resin casting; the clarity of his explanations and descriptions and the economy of his words was a joy to behold.

That fat guy, who's name I did not catch, introduced me to the two-stage, vacuum/ pressure technique. He taught me ... now, I teach you. Pass it on!

(In this game there are no 'secrets'. Only small dicked, stupid, insecure assholes who think there are secrets for them to hold close to their breasts. Jerks!).

The only cast metal item on this job is the rotor (propeller). I employed both gravity and centrifugal force to drive the molten metal into the thin blade cavities of the tool. I preheat the tool to about two-hundred degrees before using it to insure that not too much heat is sucked out of the metal as it's introduced into the tool through the tall sprue channel. The height of the sprue channel is critical, producing a 'pressure head' -- the taller you make it the more pressure is produced at the bottom, where the cavity representing the desired rotor shape is. However, too tall a sprue and too much heat is given up into the rubber and the metal freezes (changes state from liquid to a solid) before completely filling the cavity of the tool. So, I enhanced the ability of the molten metal to find its way into the thin blade cavities by rotating the tool about its sprue access. Gravity and centrifugal forces, working in concert.

Here you see the modified blood-separation centrifuge I used for both metal and

specialized resin casting. The sprue hole of the tool is positioned at the machines center of rotation. When the tool is up to speed, molten metal is poured in and immediately the metal falls down the sprue channel and flung outward into the tiny blade cavities. I get perfect castings every time! All that is left is to saw off the sprue and face both ends of the hub on the lathe.

For fine adjustment of centrifuge table speed I use this Dremel speed-controller. There's a speed dial on the centrifuge, but the settings are too course for my work.

Only on rare occasions do I find a resin casting problem that won't be resolved by either pressure, vacuum or a combination of the two processes. An example of a resin casting chore that is best done by a centrifuge assist is the casting of the tail-cone with attached pre-swirl stator blades. Spinning the tool up on the machine after introducing the resin is a surefire was of making sure that a complete fill of the tools stator blade cavities is accomplished.

This is the most complicated tool of those built to make the enhancement parts for the OTW 1/100 VANGUARD project. Five pieces, all index together, the entire array of parts held within a short length of Lexan tube. A central 3/16" stainless steel rod serves as a mandrel that forms the bore of the rotor shaft that runs through the center of the tail-cone casting. Right next to the central holes that accept the mandrel is a sprue hole in the top portion of the tool that permits introduction of the Alumilite casting resin I use. Typically I introduce the resin, spin up the centrifuge, stop it, pour in some make-up resin, remove the tool, place it in a pot and take it pressurize it to two-atmospheres. The result is a bubble free casting with perfectly formed stators.

A simple two-part rubber tool seen here casting up rudder and other parts. Note that I install mandrels into the tool and cast the pieces around them. Removing these brass rods produces the bores for the rudder operating shafts and a hole in the upper vertical stabilizer piece through which the upper rudder operating shaft passes. Within this tool is the pump-jet dunce-cap. Pay attention to the sprue and vent channeling --proper tool design is the key to complete fills and the minimum use of expensive tool making rubber.

My favorite casting resin is Alumilite 'tan.' Here you see the scale used to measure the part-A and part-B constituents of the resin. The spray can is a silicon oil mold release, used to coat the inside of the tools prior to assembly -- needed to extend the service life of the tool. This stuff, once mixed only has a pot-life of ninety-some-seconds, so one the two parts of the resin are placed in the same container you have to work quick and smart.

Most of my pressure casting is done within a 'paint pot.' I have four of these in my shop. Normally this item is sold to professional painters who do industrial type spray applications. With the regulator removed these pots are a quick and cheap way to acquire a pressure vessel for resin casting. You can get these for about fifty-bucks at Harbor Freight. The same pot can be used as a vacuum chamber, without modification (other than gagging the relief-valve).