I remember very well that series about the scratch construction of the Dove, I was a modeler at the time and I was amazed by the enormous wisdom and skill of Merriman ... and I still am.
... and if I ever find the author of that piece I will gladly serve the 20 years-to-life sentence I get for what I would do to him! I was particularly taken aback on how gleefully Steve Iverson (the Administrator/Moderator of CultTVman) embraced and published that awful, awful article.
(to be honest, for a moment, his article was a total scream, both Ellie and I loved it!).
I never use bandages! That's what God gave us super-glue for!
Well, Fred's big 1/72 THRESHER is about done. As you may recall, this is a re-build necessitated by a broken horizontal stabilizer and massive failure of filler used to fair in the longitudinal edges of the upper and lower hull halves. All the painting and weathering completed, time had finally come to assemble the control surfaces, propeller, anchor, and sail to the hull proper. As is my practice I endeavor to make the models appendages removable, secured with mechanical fasteners where ever possible. So, final assembly was accomplished in less than an hour.
Here the resident goof-ball attempts to stare down the camera. Moron. Don't know why I keep him around. He should be busting tables somewhere!
The two planes were inserted into the sail and their linkage made up. Then two machine-screws were run up through the hull to hold the sail in place. You can make out the bell-crank, which terminates in a magnet, projecting into the hull. Later a push-rod makes up to the bell-crank magnetically – the means of angling the planes for fine depth control when running the submarine below the surface.
Within the upper hull you can make out the snorkel induction mechanism. The float acts to shut off the induction line to the SubDriver (SD) when the model submerges. On the surface the float drops, opening the snorkel, permitting the SD to draw air from the surface to blow the ballast tank dry.
Each stern plane had its own bell-crank and push rod – the two ganged together, as you see here, to work as one. The rudders, on the other hand, were joined together through a common 'yoke' that permitted the centrally running propeller intermediate drive-shaft to pass through that linkage without interference.
The propeller secures to the back end of the propeller shaft with a set-screw. The forward end of the propeller shaft makes up to a Dumas type coupler which in turn makes up to a Dumas dog-bone universal fitting at the after end of the aluminum intermediate drive-shaft.
The forward ends of the stern plane and rudder push rods terminated in magnetic couplers that interfaced with couplers projecting from the motor-bulkhead of the SD.
Starting with the THRESHER/PERMIT class, American attack submarines started placing their anchor aft, in the free-flooding 'mud-tank'. This radical move made because of the new, all encompassing use of the bow for the active and passive sonar elements. There just was not room in the bow for the anchor, haws pipe, windless, and chain locker. Also, they did not want rattling chain and a clanking anchor and stem making the sonar guys deaf.
The anchor, a resin part cast with an embedded threaded stud, was secured against the side of the lower stern with a single nut.
See how the SD and control surface push rods make up magnetically. Note the centrally running intermediate drive-shaft.
No no…that is a perfect rendition of the splashdown into the La Brea tar pits.Kidding! I’m afraid Datin’s ghost will attack me if I even try to paint a 1/350 Enterprise.
Did anyone ever do the HLLV from JOURNEY TO THE FAR SIDE OF THE EARTH
No no…that is a perfect rendition of the splashdown into the La Brea tar pits.Kidding! I’m afraid Datin’s ghost will attack me if I even try to paint a 1/350 Enterprise.
Did anyone ever do the HLLV from JOURNEY TO THE FAR SIDE OF THE EARTH
Did you perhaps mean Journey to the Far Side of the Sun, aka Doppelgänger, instead? Because planet Earth really doesn't have a far side these days anymore, other than the vintage Gary Larson cartoons, that is...
The last couple of months has kept me busy readying some of my r/c model submarines for the two big events of the year, both occurring during the month of September. Now that those obligations are out of the way, I continue my work (and this WIP report) on several in-progress modeling jobs. This installment I re-join the effort to restore a HUNLEY model sent to me by a friend who wants to get it fully functional and back into the water.
The real Confederate HUNLEY was a privateer built to sink Union blockading ships during the American Civil War. The craft, though lost with all hands on its last mission, did in fact record histories first successful engagement between submarine and ship – the actual HUNLEY has since been found, salvaged, and currently undergoing restoration.
This model, though flawed as to proportion and detail, is a close enough representation of the HUNLEY as to warrant my full attention and efforts to get it into presentable shape as to look and function. So, with my shop restored to proper order I took the long suffering HUNLEY model down off the wall and did a quick survey of what had been accomplished (yeah... it's been that long!), and what work remained to be done to get this beast operational.
I had already worked out the gimbal mechanism for the propeller (as the HUNLEY had no stern horizontal control surfaces it would have been unmanageable about the pitch axis submerged above any speed where dynamic forces overcame the boats natural pitch stability); and installed the rudder control-rod (henceforth properly referred to as the 'rudder torque rod') bushing. So, last night I manufactured the rudder and got a good start piecing together that very Rube Goldberg'ian rudder control linkage. Could the Southern marine Architects have made a more complicated means of banging that big rudder around??...
Damn!
Long before the salvage of the HUNLEY we had a very good look at what the actual boats rudder mechanism looked like, in the form of a beautiful, miniature painting by the period Civil War chronicler, Conrad Wise Chapman.
His pencil studies and eventual painting of the HUNLEY – presumably representing the boat either awaiting a mission on a pier, or undergoing a post sinking restoration (there were several such disasters during the boats career) – became the sole document to accurately illustrate the arrangement and function of the HUNLEY's rudder mechanism. I recommend you check out this site for more on the Artists and this particular painting: Conrad Wise Chapman - Wikipedia
(You old-time r/c model airplane guys will recognize the HUNLEY's rudder mechanism as one very much like that used on single-channel model aircraft that employed a rubber-band powered actuator, charmingly referred to as an, 'escapement', to position the models rudder (often the only r/c function aboard the model aircraft... those were the days!).
The Internet is a wonderful resource; a quick find about the possible (and now 'actual', owing to the recent discovery of the actual boat) workings of the rudder mechanism garnered me photos of well done models, and illustrations identifying the key components of the mechanism. With that information in hand I started proofing my ideas through a series of shop sketches – that process helping me segregate out the loopy ideas from the sound ones. Here I've sketched out how I would integrate a brass tube rudder bushing to a Sintra plastic sheet rudder.
(Sintra is a trade-style for a polyVinyl Chloride plastic sheet with hard faces, and a foam core – a useful model-building medium).
Note the use of two soldered brass extensions to strengthen the attachment of plastic to metal. Pasted to the corners of the sketch are copies of rudder mechanisms pulled from various sources – these guiding me as I created my own practical rudder mechanism.
The 3/32” o.d. brass tube -- sized to sleeve within it a 1/16” diameter brass rod – with its two soldered brass batons was CA'ed to the leading edge of the Sintra rudder after cut-outs for the batons and central bail-bolt slot is cut out with an #11 knife blade.
A big virtue to Sintra is that its thin hard surfaces and soft inner core are easily cut and require little pressure to penetrate. Yet this low density material is very resistant to torsional loads; is relatively heat stable; and takes to adhesive, cohesive, primers and paints beautifully.
Here I'm using the CA-baking soda to adhere the parts and fill gaps between brass tube and batons and the rudder proper.
After each application of CA and baking soda, just as soon as the mass hardens (which takes only seconds), I knock down the high spots with file and a lot of elbow-grease. Eventually I'll coat over the CA-baking soda filler with touch-up putty and wet sand the entire assembly, getting it ready for primer and paint. But, that's for later.
I took a brief break from working out the rudder mechanism linkage... it was making me crazy... and engaged in some emergency aggression therapy. How? By going Mid-Evil with pliers, torch, and a crazed look on my face. That's how!
Some internal hull structures needed removal to make room for the eventual 2.5” diameter water tight cylinder that would contain the propulsion, control, and ballast sub-systems.
The epoxied-in-place wooden foundations were easily pulled out with pliers, as were the two brass pieces of fixed ballast. But the two massive bow plane bushings refused to budge!
At room-temperature those bushings resisted my twisting and pulling with pliers; they just refused to budge.
(Sorry, Zed, time for a little torch action. Pucker up, pal!).
But, heated...
… out they came!
The heat weakened the glue. But before all that I had to protect the surrounding structures from the heat by placing water soaked wash-cloths around the base of a bushing as I applied the heat. In no time at all the glue failed and it was an easy matter to yank the bushings from from the hull. Finally, I had all the room I needed for the 2.5” WTC.
With obstructions removed from the hull I returned to the rudder mechanism.
Needed to interface between the WTC's rudder servo and torque rod was a bell-crank. Here you see the completed bell-crank test-fitted to the forward end of the rudder torque rod. It was constructed from an .092” bored Du-Bro wheel-collar and a scrap length of .25” X . 030” brass strip. The two soldered together.
Here's an over-view of all the pieces that make up the HUNLEY's rudder mechanism. The three square 'nuts' started life as a length of plastic model kit sprue. I simply shaved the round sprue into a square section, drilled a 1/16” hole through the end, then razor sawed the required number of nuts. These friction fit retainers were use at the sliding-bail transverse pin, and at the end of the sliding-bail swing-arm engagement pin.
Using a gimbaled propeller to effect pitch control of the model submarine is not a new solution for me. I had to do the same thing on two Disney NAUTILUS models I assembled in the past – a submarine that did not employ proper stern planes (those strake embedded horizontal control surfaces are useless in the real world). Not only did those Disney NAUTILUS models pitch the propeller up-and-down, I made it so the propeller could also translate left-and-right for yaw control. The propeller pitching mechanism for the HUNLEY is substantially easier than what I manufactured for the Disney NAUTILUS models.
I turned an impractical fantasy submarine into a well running r/c model submarine without resorting to the ugly compromise of adding un-scale horizontal control surfaces. Look over this video to see the means and the results:
So, I'll be doing pretty much the same thing for the HUNLEY which also had no viable means of controlling the submarines pitch-angle once submerged.
Getting back to the current project for a moment, here is how I will pitch the HUNLEY's propeller for submerged depth-control: Divide the propeller shaft into two halves; place a universal joint between the WTC's motor shaft and the forward end of the forward half of the propeller shaft; connect the two propeller shafts with a simple flexible-hose universal; place a single-axis gimbal at the propeller end; and come up with a means of pushing either end of the propeller shaft up-and-down to direct the propellers thrust line above-or-below the vehicles center of mass. Easy peazy.
With the NAUTILUS jobs I came up with this means of pushing the propeller shaft up-and-down. Keep in mind that this is a complicated affair. Made so, in that example, by the need to produce both pitch and yaw deflections of the propellers thrust line. The mechanism I make for the HUNLEY will do only pitch deflections – it will be a much simpler affair.
The pitching propeller mechanism started life as a full-scale profile shop-sketch of the models stern. This paper-study helping me noodle things out as I mocked up the components of the system. Here I've already cut the 1/8” diameter stainless steel propeller shaft into two pieces; pressed lengths of brass pinion gear wire into each shaft to serve as splined flexible hose retainers (one already press fit into the after length of propeller shaft); identified and bored out a commercially available universal joint to interface between WTC motor output shaft and forward length of propeller shaft; and, at the extreme right over the drawing, the after length of propeller shaft, propeller and single axis gimbal.
I could have gone with a proper universal joint, like the one hanging off the ass-end of the WTC, but I like simple. The only trick to using flexible hose (silicon being my material of choice) is to employ a hose of substantial diameter and wall thickness to resist twisting as torque increases between motor and propeller. The splined shaft ends insures a non-slip attachment between hose and shaft halves.
The shop-sketch indicates a ten-degree deflection – which this mechanism can achieve with minimal loss to friction – but experience shows that submarine pitch angle maintenance and change can be effected with as little as a three-degree deflection about the pitch axis.
Within the after propeller shaft gimbal is a set of Oilite bearings that insure a well lubricated and low friction fit between gimbal and running gear. The pivot point of the gimbal is about those two pins projecting from the after end of the gimbal. Those pins fit slits of the gimbal foundation glued into the after end of the running gear stern-tube. Several stainless steel washers between the forward face of the propeller hub and after face of the gimbal will serve as ahead thrust bearings.
A similar arrangement within the WTC motor-bulkhead will handle the astern loads.
To drop the WTC low enough onto the wooden frames within the lower hull – placing its motor shaft in alignment with the boats longitudinal axis (shared by the propeller shaft) – required grinding away a significant portion of the frames upon which the WTC would eventually sit. I could just barely get a moto-tool in there to accomplish the rough shaping.
As I ground away the frames to contour I identified the high spots by placing a cylinder, coated with white oil-paint, down on the work, which left white smears on areas of each frame that needed more grinding. This process continued until the WTC motor shaft shared that of the hulls longitudinal axis.
Final shaping of the semicircle indentations in the HUNLEY's frames was done with a scrap length of 2.5” diameter Lexan cylinder (same diameter as the eventual WTC that will be mounted in the hull) used as a form to sand the frames to contour.
Note that I've installed a Velcro strap that will be used, along with an indexing pin (yet to be installed) to register and hold in place the models WTC.
FINALLY! The propeller pitching mechanism has been manufactured, installed, dialed in, and found to work as planned. This illustration is a quick look at its function and the call-outs will help understand the following narrative as I employ proper terms to the various components.
The final configuration differed little from the initial full-scale shop sketch of the propeller pitching mechanism. The only significant change was to adopt an Oilite bearing element against the after propeller shaft length instead of the wire 'cage' I used on my NAUTILUS models. We grow as time marches on.
Use of a card-board mock-up bell crank to scull out the proper distance between input and output points in relation to the pivot point. A few of these card-board studies and I had the desired shape and distancing. The mock-up was pulled and used to mark off a thick piece of brass sheet from which the actual bell crank would be manufactured.
Using the card-board mock-up as a stencil to mark off the shape of the eventual brass-sheet bell crank. Note that I've added a big tab at the bottom of the bell crank – this will be eventually bent back ninety-degrees to form a pusher plate against which the pitch servo push rod will act.
Sawing, boring, and finishing the bell crank.
The bell crank features two brass tube bearings. One for the bell crank pivot pin. The other (the one being soldered in place here) for the tensioner perpendicular shaft.
The bell crank is free to rotate about its pivot shaft, and the attached tensioner is free to rotate as the after propeller shaft piece pitches up and down. Note the retaining collar between the hull and bell crank pivot bore. That collar and the removable Du-bro wheel-collar, near the WTC universal, sets the lateral position of the tensioner and insures that the propeller shaft elements do not move laterally, only vertically.
The propeller pitch tensioner not only had to force the after shaft section up and down, it also had to translate as the angle of that shaft changed. This required the tensioner to be support by a perpendicular shaft that would be free to rotate within the bell crank during operation. Here I'm soldering that shaft in place onto the short tube section that would mount the eventual Oilite bearing, seen in background.
It's my practice to have a pad of post-it-notes in every room of my house – especially the bathrooms! – as I never know when a good/bad idea will pop into my head. I have even, on occasion, jumped out of bed in the middle of the night to jot down something that came to me in my sleep. Here are but two of the many sketches I worked up as I wandered about thinking of how things could go together with the HUNLEY's propeller pitching mechanism.
Here I'm sliding a 1/8” bore Oilite bearing into the body of the still-in-work propeller shaft tensioner.
Peening the Oilite bearing in place within the tensioner with the aid of a spring-loaded punch. This is done with a stainless steel length of shaft in place to prevent deforming the bore of the Oilite bearing during this operation.
A bracing gusset atop the hull holds the rudder torque rod tube firmly in place.
Within the after portion of the HUNLEY's hull you can make out the propeller pitching mechanism: The WTC with output motor shaft made up to a universal joint; to the right the bell crank with attached 'floating' shaft tensioner; and, almost out of sight, the spline with slipped on flexible hose 'universal' that interconnects the forward and after sections of propeller shaft.
Here's a good shot of the installed propeller pitching gimbal. Note how the foundation that girdles it has been scalloped out top and bottom to permit the gimbal to swing up and down. You can just make out the press-fit Oilite bearing within the gimbal that provides a low friction bore through which the propeller shaft rotates. That Oilite bearing also offers a low friction surface to the transverse loads as the propeller shaft swings up and down.
I've been droning on about the HUNLEY model itself for long enough. Now that you have a grasp of what I'm doing to control yaw and pitch, lets give all that nonsense a rest and look at the module I'm putting together to control, propel, and change the submarines displacement. In foreground is a preliminary fit of my water tight cylinder (WTC). In background is the cylinder provided by the client. Mine, of course, is superior in all regards: it has a ballast tank, geared motor, easy access to all internal devices and mechanisms, and room for a battery of much greater capacity.
The WTC's forward end is to the left. It's in that space that most of the electronic devices that power, control, and manage the ballast water are housed – those devices atop an aluminum tray. Beneath that is housed the single 11.1-volt Lithium-polymer battery, with enough capacity to run the HUNLEY for well over an hour.
Dividing my WTC into three compartments are two internal bulkheads. The forward space was just described, the middle space is the ballast tank, which is of the 'soft' type; that is to say, it's always subject to the ambient water pressure. The after dry space houses the geared propulsion motor, three servos (rudder, propeller pitching, and bow planes), and Low Pressure Blower (LPB) which is used to blow the ballast tank dry once the HUNLEY's snorkel broaches the surface.
What you're looking at is an initial fit-check, it is far from being a finished product at this point.
I don't pull this stuff out of magic hat. No. A lot of thought goes into the WTC. Where will the devices be arranged with one another to achieve the shortest cable-runs between them? Where to best position the devices to make access an easy matter? How much water must the ballast tank contain to achieve a reasonably high surfaced trim waterline when emptied? All these problems and more start in my brain, they begin to solidify on graph-paper, and finally, I start to mock-up the arrangement – first with cardboard stand-ins, then, when happy with those renderings, I start manufacturing the foundations and other hardware to mount the devices to get them to work together in the most efficient manner.
Such paper studies lead to simplification. The most efficient system contains the minimum number of elements to achieve the goals of the system! The initial paper studies are always over-complex plumber's nightmares. But, after examining your two-dimensional representation you see where things can be improved... you make more drawings; each one more rational than the one before. The process continues till clarity of purpose is achieved. Only then is it time to get physical!
To illustrate what clarity in my world means:
All the expensive stuff is up high-and-dry atop an aluminum tray. Down below in the nasty bilge space goes the battery. If I get a leak I don't care if the battery takes a bath, but I do want the electronic devices to stay out of the wet. In this game things eventually get wet! So, you design for that inevitable incident. Oh, I never operate in salt-water!
OK. Backing up to the beginning of the forward dry space device tray: It started out as a cardboard mock-up. Several versions of this thing were scissored out and test fitted till I had the right geometry. From that point the hero cardboard tray was used as a template to mark out a sheet of hard, .030” thick Aluminum.
Using double-sided tape (servo tape to some of you) I did a preliminary arrangement of the devices atop the tray. I was over-optimistic thinking I could also make room for the LPB (a neat little diaphragm pump-motor unit) atop the tray. That had to change! Other issues as to device locations were also identified here. It's amazing what you realize how much you missed during the paper study as you begin to apply the two-dimensional representation to a three-dimensional reality! And how quickly one is revealed to be a dumb-ass during this revelation.
So!...
...changes are made! First to the paper-study, then to the actual device tray. I found room for the LPB atop the servos in the after dry space. The extra wiring necessitated going to a larger diameter conduit that passes through the ballast tank. But, that's life in the big city! Here I've re-arranged the position of the devices. Now things are making a bit more sense. Note the device block-diagram/schematic on the left side of the drawing – this done to identify the arrangement that would give me the shortest runs between cables and leads.
I also identified where I would have to remove more Aluminum – to make a passage for the battery cable, aft. And more of an opening for the wiring that had to pass aft through the ballast tank conduit which was beneath the tray.
Here's a neat tool for making inside-cuts into soft metals of small gauge: It's called a 'nibbler'. And works just like that, a jaw and anvil that shears away small chunks of sheet-metal with each pull of the handle. It gets into places where other tools either can't or require a lot of awkward maneuvering to make the cut.
Today's electronic devices produced for the hobby industry are of an exceptionally high standard. However, it's a fools game to just plug everything into a complete system without first certifying that each device works as advertised. Such was the case with the receiver, battery eliminator circuit, electronic switch, mission switch, angle-keeper, electronic speed controller, LPB, propulsion motor, and four servos. Each one received my close examination as it was tested for proper operation.
Here I've adjusted the battery eliminator circuit to provide the 5.25-volts demanded by the receiver bus and other devices that dine from that trough. Correct output verified with my handy-dandy, wonder, multi-meter. Note the extensive use of jumper wires to interconnect the device to battery and meter.
The propulsion motor electronic speed controller was tested and its operating parameters established with the aid of a 'servo-setter'. Again, hook up was simplified with the use of jumpers. The LPB switch, and servos were tested in a similar fashion.
And that, boy's and girl's, is how I get ten-pounds of shit into a five-pound bag!
Oh!... a bonus posting. Here's a quick look at some underwater shenanigans as I mixed it up with two other submarines at the resent Georgia SubFest event:
I've almost completed the assembly of the HUNLEY's WTC; the system that will propel, control, and manage the ballast water used to transition the model submarine from surfaced to submerged trim and back again. All the sub-assemblies have been assembled and integrated into the whole. I've mocked-up all the devices and have got them to operate in concert with the transmitter that will permit remote operation of the HUNLEY model when it's operating on and under the water. The only task remaining is the routing of the wiring through the conduit, shorten some leads, make up the magnetically activated mission-switch, and integrate the WTC with the HUNLEY's linkages.
The Forward Dry Space A removable forward bulkhead pops on and off for easy access for battery swap or to get at the devices mounted above the battery. By removing two mounting screws the entire device tray can be slid out for even better access to the devices, enough slack in the power and control wires has been provided for this. The receiver antenna has been wrapped around a mandrel eliminating the need to run the antenna external of the WTC's cylinder. On the dry side of the forward ballast bulkhead resides the ballast servo.
The Ballast Tank Within the ballast tank is a gas bottle and blow valve to provide an emergency back-up means of blowing the water out. The receivers fail-safe point for that channel has been set to drive the ballast servo to full extension in the 'blow' position should the receiver fail to see a transmitted signal. At all other times the transmitter sends only enough 'blow' position to activate the LPB, but not enough travel to engage the emergency blow valve. Normal blow is via LPB only. Emergency blow both the LPB and gas source work to discharge ballast water.
The After Dry Space Within this space is housed the motor bulkhead with installed 380 sized motor that is geared 3:1 to the drive-shaft. Set into the motor bulkhead are three servo pushrod seals and single drive-shaft seal. Mounted on an aluminum tray on the dry side of the motor bulkhead are the three servos (rudder, bow planes, and propeller shaft pitching mechanism), and on the other side of the tray is mounted the little diaphragm pump-motor (LPB) used to blow air into the ballast tank during a normal blow operation.
For over three decades we manufactured and sold hundreds of WTC's to the world market. Now retired I make occasional use of the jigs, fixtures, templates, and parts still at hand in the shop for the occasional 'fun' job like this. Here I'm using one of the 2.5" diameter mark-off templates to identify fastener, vent, and flood-drain hole locations that will be drilled and machined out.
Poly Vinyl Chloride (PVC) Lexan plastic is very tolerant of drilling, milling, and grinding and will not crack or craze as readily as the cheaper and more available Acrylic plastic. Lexan has been our cylinder material of choice from the beginning. Here I'm drilling a starter hole that will later be milled out as a square hole to accommodate the ballast tank vent valve body. The cylinder for this job is 2.5" in diameter with a wall thickness of 1/16".
The brass tube conduit permits dry passage of the power and control cables and leads between forward and after dry spaces. Here I've attached the two internal ballast bulkheads together with the aid of the conduit to demonstrate how the bulkheads divide the cylinder into three discrete spaces. As you can see the cylinder has already been machined with ballast tank flood-drain holes and holes for the internal bulkhead securing screws. Installed are the ballast linkage bell crank within, and the tank vent valve atop the cylinder. The black Electrician's tape covers the holes that pass the ballast linkage bell crank and hold its pivot pin in place.
As this particular WTC had to pass many more cables and servo leads than the mass-produced varients of the WTC's we sold, a bigger diameter conduit was needed. So, I drilled out the original cast-in-place O-rings that made watertight the original, smaller diameter, conduit -- you see, in cut-away, to the left, one of the stock ballast bulkheads demonstrating the cast-in-place O-rings typically used. As you can see the new conduit is much larger in diameter. That meant fabrication of a new set of sealing O-rings for the ballast bulkheads.
The two brass nipples you see inset within the after ballast bulkhead will eventually make up to lengths of flexible hose. That plumbing will route air from the surface -- through the HUNLEY's snorkel tubes -- to the LPB which will discharge that air into the ballast tank, blowing out the ballast water during a normal blow.
In foreground are cut-aways of the shaft and pushrod seals we produced and used with our line of WTC's. It's all about keeping the water out and the magic in!
To the left is a typical seal designed to make watertight a rotating shaft. The sealing element is a rubber 'cup seal' that features a chevron shaped inner and outer lip that makes a light but effective seal between shaft and seal body. This type seal is best employed for shafts that rotate instead of traveling axially. However, manufacture is labor intensive as the plastic resin body requires lathe work. Adding to the seals complexity is the need of a close tolerance Oilite bearing to prevent wobble or lateral motion of the rotating shaft within the seal body -- if unrestricted such motion would unseat the seal, resulting in water getting past it; that bearing is there only to keep the shaft centered, not for axial thrust loads.
For making watertight axial traveling shafts, such as pushrods, simple embedded O-rings within cast resin bodies suffice. Two sizes on display here, 1/8" and 1/16" diameter pushrod seals. Note that the smaller pushrod seal features two encapsulated O-rings, a recent improvement -- a bit more friction, but a sure-fire water-stopper.
Once an appropriate diameter of brass tube was identified to serve as this WTC's conduit I selected an O-ring diameter that made a slight interference fit to the conduit, then milled into one side of a ballast bulkhead a depression that made a slight interference fit to the outside of the O-ring. The two O-rings would make watertight the conduit where it penetrates the ballast bulkheads. Each O-ring is held in place with a RenShape retaining ring secured in place with CA.
The conduit O-ring retaining rings were turned from a raw chunk of dense RenShape model-making medium. Here, my over-achieving Taig lathe is pretending to work like a turret-lathe. I love these machines: simple, sturdy, and great support from the factory when you need accessories and repair parts. If you don't have a Taig lathe... get one!
I needed two retaining rings, but three gave me a little 'insurance'.
And here are all the sub-assemblies ready for installation within the Lexan cylinder of the HUNLEY's WTC.
This shot gives you some appreciation why I had to engineer a larger diameter conduit -- that thing was gonna be fed a lot of spaghetti! The power cables to the LPB, The power cables to the propulsion motor, and the three servo three-wire leads would all pass through the ballast tank.
I disassembled the motor bulkhead and pulled the devices off the tray to give you an idea of what all the nonsense back aft is about. The cast resin motor bulkhead is made up of the forward motor-mount which bolts to the forward face of the motor bulkhead proper. Sandwiched between the two parts is the pinion gear that drives the motor-shaft. That shaft passing through a cup type watertight seal. Set into the motor bulkhead and projecting into the water are the watertight seals through which the servo pushrods travel axially, and the motor shaft rotates. On the bottom of the tray sits the three servos held in place with servo-tape and a bracket. On the bottom face of the tray is the servo-taped LPB.
Before stuffing all the cables and leads through the conduit I hard-wired everything together with jumpers and operated the devices as a system. So configured any problems are easily fixed with things still accessible. Much better than if I had to fish leads and cables out of the tight confines of the conduit with the inevitable need to de-solder, fix/replace, then solder things back together.
Well, after about two-weeks of work I got this little HUNLEY WTC to work as advertised. Here I'm doing a practical in-water test of the systems ballast sub-system. The hose under my thumb leads to the suction side of the Low Pressure Blower (LPB) diaphragm pump. When the inlet side of that hose is in the air, such as when the model submarine broaches the surface in preparation to surfacing, the LPB is turned on, compressing air and blowing it into the flooded ballast tank, blowing out the water, lightening the boat, causing it to surface and assume surfaced trim.
Most r/c submarine transmitters are configured like aircraft as to specific stick and switch function, what is called, 'mode 2'.
Typical r/c submarine transmitter controls go like this: The two-axis stick on the right hand side of the transmitter: Bow planes, up(rise)/down(descend). Rudder, turn right/left.
The two-axis stick on the left hand side of the transmitter: Throttle up(ahead)/down(astern); ballast water, left(vent)/right(blow).
The stern planes, in the special case of the HUNLEY model, controls the propeller thrust line about the pitch axis, counter-clockwise(rise)/clockwise(dive). Its the knob seen atop the right-hand side of the transmitter case.
This picture denotes the happy ending of a long, and sometimes frustrating process of getting the system organized, assembled, and working in some semblance of a coherent whole.
I needed to extend the three servo leads to lengths that would not only interconnect the two dry spaces through the ballast tank conduit, but would also be of significant length to afford the slack required to pull both the forward device tray and after motor-bulkhead clear of the cylinder ends. Initially I simply soldered on extensions to the servo leads, but later found that the added thickness at the solder unions became an interference issue within the conduit. Rather late in the game I was forced to abandoned the soldered extensions and substitute three-wire servo leads of appropriate length from a bulk spool I had at hand. The soldered unions in this case occurred back in the after dry space, well clear of the tight confines of the conduit.
The ch-4 output from the receiver controls the ballast sub-system servo and LPB electronic switch (2IS). As power and signal is shared between the two devices I soldered together a Y-connector to control the two devices from one input, that work underway on the left side of the photo.
The two heavy wire pairs below are for the LPB (white wires) and motor (black wires). These pairs, along with the three three-wire servo leads, all eventually run from the forward dry space, through the ballast tank conduit, and into the after dry space.
Soldering is straight forward using 60/40 (Lead/Tin) rosin core solder, a 25-Watt iron, and a non-acid liquid flux. Wires are first tinned, secured in some holding device, heat applied to adhere the wires together, and everything insulated and made nice and tidy (and, as it turned out with the three servo leads... too damn bulky to fit the conduit!) with heat-shrink tubing. I should have staggered the length of each wire of a three-wire lead. But... nnooooo! I piled each splice atop the other like a moron. Lesson learned!
I made use of the excellent little KME magnetic mission-switch. This device permits on/off operation of the system by the simple wave of a magnet over the switches sensor. This type switch eliminates the need for the bulk and complexity of a typical toggle-switch outfitted with a watertight boot. Here I'm wiring it up the magnetic switch to the system.
Not many are into the r/c vehicle game as deeply as me, but years ago I found that by shelling out the money for a proper crimping tool and sets of crimp-on connectors specifically designed for the type-J connectors (favored by all modern makers of r/c equipment) a great deal of time, and space within the tight confines of a WTC could be saved by making up my own leads and/or shortening existing ones.
Here I'm demonstrating how the process works. A big advantage to the type-J connector is that the crimped in place pins can be removed from the plastic body easily -- without damage, to permit running of the (typically three) lead wires through the tight confines of a conduit -- and re-assembling once on the side of the conduit.
Note how I've secured the KME mission-switch atop the RenShape foundation with two loops of sail-twin. Sometimes the old stuff is the best stuff.
That green painted Iron doughnut is an inductive spike smoother-outer. Overkill for this job and the damned thing took up too much real-estate -- had to go! I get an unwanted DC pulsing from the battery eliminator circuit by doing that, but today's receives are smart enough to filter that minor fluctuation out at the front end and process the pulse-train just fine.
The KME magnetic switch will eventually be mounted atop that brown, RenShape plastic foundation glued to the forward end of the device tray. This places the sensor close to the top of the WTC's cylinder so that there will be a short distance between it and the activating/deactivating magnet that will be swept by the WTC to turn things on and off. That foundation is also a strain-relief block for the cables that run to the battery-system Deans connector.
I've already run the LPB and motor power wires through the WTC's conduit. And everything has been wired up and connected except for the three servo leads.
Before cramming the three servo leads into the already tight conduit I did a complete systems test. I've just turned the system on with a magnet and will fiddle all the sticks and knob to make sure everything works as advertised. Note that I have yet to mount the mission-switch or remove the BEC's choke doughnut. This initial systems test a preliminary -- you don't want to get too far ahead of your skies: if there is going to be an issue make that issue apparent because of one or two steps taken since the last test, not a whole series of operations since the last test. Make trouble-shooting a whole lot easier if you can keep the number of suspects to a minimum during fault identification. In the Navy we called it, 'Easter egging'.
AND THAT, SPORTS FANS, IS WHERE EVERTHING WENT SOUTH!!!!
I mounted the tray into the forward dry space, and started to route the servo wires through the conduit. NO GO! Those fat splice points along the length of the leads would jam within the conduit. And that's what made me chop these leads off close to the servos and graft on three lengths of virgin lead from my stash of three-wire lead. That took an evening, but I was then able to fit the three leads into the conduit!
A final dry run-up of the installed and buttoned up system and... amazingly... it all worked. Hell yeah! Suck it, Murphy!
First practical test, an important one, is to check for leaks. At either end is mounted a tire-valve (Schrader-valve) on a bulkhead.
When you push home the last of the two end bulkheads, it creates a slight over-pressure within the cylinder. That over-pressure is dumped by depressing the Schrader-valve stem momentarily to get the interior of the WTC equal to that of atmospheric pressure.
To leak-test the WTC I remove the core-valve from the valve body and press-fit a length of flexible hose. Submerging the WTC underwater and blowing on the hose (while doing so, firmly holding the two outboard bulkheads on tight so they don't pop off) will cause any leakage points to bubble and reveal the exact point of leaking. In this case, the WTC passed this test the first time. The hose removed and the core of the Schrader-valve re-installed (only an idiot would forget to put the core back in before the next in-water test... guess who!).
Mike Bratley, formerly a rag-hat bubble-head (he actually served as crew aboard one of the DSRV's in the day!) is today a high-ranking COD driver (you know, those uglier than sin, gray, turbo-prop flying mail-trucks used aboard Carriers). In his off-hours, which are few, he's a bit of a model-builder. He's into r/c boats, high-power rockets, and now r/c submarines.
He dragged my sorry butt into his first r/c submarine project, a 1/72 Revell SKIPJACK. Not taking my advice to 'start slow' -- to keep the system components as basic as possible so he could learn and enjoy the many frustrations even a simple r/c submarine will present -- he completely ignored me and jumped into fancy lighting and autonomous control circuitry. What he needed me for was help with the fully retractable mast array!
Holy-shit! His first r/c submarine?!...
Normally I dismiss this kind of thing as stupid-talk. But, he's almost finished with it, and from what I've seen, it's a rational, well thought out piece of work. Only hiccup is the means of translating the mast actuation servos unusually long travel from a motion that originates along the submarines longitudinal axis to a sharp 90-degree bend upward to push the masts up, and pull them down on command.
At his place Mike handed me what appeared to be a length of stainless aircraft quality control cable (wonder where THAT came from?!), and sent me on my way after forcing me to eat steak and consume massive quantities of diet Mountain Dew. I told him I would work the problem back at the shop. And here are the gory details of what I came up with:
So I came up with this mock-up of a three pulley mechanism to translate cable motion by 90-degrees. Nothing new here, airplanes have been doing this for over a hundred years.
However, as the stainless steel cable was rather stout it experience a lot of internal stress and friction as the lay of the individual wires rubbed and twisted against each other as they negotiated the tight radius turn offered by the one-inch diameter main pulley. I know that Mike's servo can deliver the force to move the cable, but the weak link in his linkage is the magnets used to couple servo travel, within the SD, to outside travel, external of the SD. The experiment points to the need to find a more flexible cable material -- one that won't bind up when stressed like this. We're on the right track, but need to experiment with different type cabling.
Most hair-brained ideas are first sketched out to get a better feel of the mechanics involved. Here a isometric of the pulley arrangement is presented graphically. It's at this point in the design process that you identify the size limitations of the environment it will fit, which drives the size of the mechanisms components. I settled on the main pulls diameter being one-inch. That, along with the two smaller pulleys, and eventual frame that would support the pulleys, the entire mechanism would have to fit the narrow annular space between SD and the hulls inner surface.
A simple lathe job turning some machine-brass round-stock to size and shape. I've completed the main pulley and am just about finished with the two smaller ones, still chucked up and ready to be parted away.
Brass pins press-fit into holes drilled into some particle-board with a nice, clean white veneer. The pulleys rotated freely about these pins.
The pulleys secured with wheel-collars, the cable reeved between the pulleys, and a determination of the force required to overcome the friction caused by the twisting wires within the lay of the cable.
Ouch!
Nearly a half-pound of force required to get the cable in motion. That won't do at all! We've got to come up with something of similar diameter, nearly as stout, but producing less internal friction when traveling over a tight radius pulley.
Today I went from mock-up to practical three-pulley fairlead. I was delighted to find that the drag of the mechanism went down to only five-ounces. Not bad. I think Mike can work with that.
With the linkages for the pitching propeller and rudder worked out in head and on paper, things moved to manufacture, installation and... after the usual bumps in the road... successful operation. The rudder would wag, and the propeller would pitch up and down.
The bow planes.
Time had come to work out a practical linkage to connect the outrageously heavy HUNLEY bow planes to the WTC's bow plane servo.
Here's the end-game of the work required to interconnect the two bow planes. That U-shaped item between the planes is a 'yoke', needed to achieve clearance over the installed WTC. The inclusion of that WTC negated the ability to run a simple, one-piece bow plane operating shaft between the planes.
Nothing's EVER simple or easy!
The control horns used to rotate the control surface operating shafts were made from DuBro wheel-collars soldered to strips of brass sheet. A finished horn attached to its operating shaft of the bow plane on the right, parts of a soon to be assembled control horn next to the bow plane on the left. Note the flat milled to the end of the operating shaft that fits the bow plane.
This shot also denotes the three means of active control of the r/c model HUNLEY: The pitching propeller, used to vary and maintain the pitch-angle of the submerged submarine; the linkage used to swing the rudder for yaw control; and the means of rotating the bow planes to make fine adjustments to the submarines depth when running submerged.
Initially I planned to put a control horn to each bow plane operating shaft but found that it would be easier to run a yoke between them rather than employing a two-legged pushrod (with each leg engaging an operating shaft control horn). As the eventual yoke carried both operating shafts, I needed only one horn and one push rod. KISS! (Keep It Simple, Stupid!).
The WTC's servo pushrods terminated in magnets which matched up to corresponding magnets that continued the linkages to the mechanisms that swung the rudder and pitched the propeller. Here is a look at the magnets and how they were secured to the push rods and bell-cranks.
The example to the right is a completed magnet assembly secured to a length of 1/16" diameter brass rod -- the same type rod that passes through the WTC's watertight seal. Note that the position of the magnet on the rod can be adjusted by simply loosening a set-screw, repositioning the magnet along the length of the push rod, and re-tightening the set-screw -- great for 'centering' a control surface.
A sterling example of how the use of magnetic couplers, as elements of a linkage used to control mechanical functions outside the WTC, is this array of pushrods at the after end of this 1/72 GATO's WTC. The magnets interconnect the rudder, stern planes, bow plane deploy/retract mechanism, and bow planes to the WTC. Use of these magnets permits quick, easy, no-tools-required attachment and offer near zero back-lash.
I was faced with little wiggle-room back aft so had to get creative when designing the linkage elements between rudder servo pushrod and torque-rod that drove the rudder mechanism. First, a paper study; then a cardboard bell-crank to check for fit (three efforts there before I had one that worked); then cut out of the actual bell-crank from brass sheet and bend to shape. Check twice, cut once!
I turned brass bushings for the bow plane operating shafts from machine-brass. Here I'm dunking the finished parts in Ferric Chloride acid. This quickly oxidizes the metal, a process called 'pickling', producing microscopic pits onto the parts surface. This to enhance the 'grab' of the glue to the brass part by vastly increasing the surface area of the part engaged by the adhesive, producing a strong bond. After pickling the part (and... oh, yeah... my fingers) are douched in water spiked with baking soda to kill the acid. Things are then rinsed with fresh water, dried, and ready for bonding (and nose-picking).
Here I'm CA'ing one in place within the well left after I yanked the massive original aluminum bushings -- those pulled early on in this restoration effort to make room for the WTC. That transverse rod is a stand-in for the eventual bow plane operating shafts, there to insure that the bores of the two installed bushings are inline with one another -- care was taken not to get any glue on that! I built up fillets around the bushings with baking soda saturated with CA adhesive. The high pH of the powder insures a quick cure of the adhesive and becomes hard as a rock in seconds.
As I had nothing to do with the fabrication of this HUNLEY model I sometimes found myself amazed at some of the engineering behind this representation of this historically important war vehicle. A pleasant aside from the many obvious wrong turns was the approach the original model-maker took to represent the make-up of the bow plane operating shaft to the bow planes. As the actual control surfaces of the HUNLEY -- the rudder and pair of bow planes -- were likely cut from iron plate the most rational means of attaching the round operating shafts to the planes was indeed practiced on this model: mill flat the outboard end of an operating shaft, place it onto a face of the control surface and make it fast with a riveted retainer plate. Likely what the real submarine had and a practical solution on the model itself.
All I had to do was mill flats at the ends of the two bow plane operating shafts, slip them into the bores of the control surfaces and make everything fast with CA adhesive.
Complicated assemblies to be welded, glued, or soldered sometimes benefit by the use of a holding fixture to secure the pieces in correct alignment as they are fixed in place. This arrangement of aluminum tube, machinist's vice, and anvil all pressed into service to hold the two wheel-collars in alignment and correct spacing as the yoke are is soldered to them. Not pretty, but functional.
Why an aluminum tube? Because typical solders won't adhere to aluminum!
Yet another quick-and-dirty holding fixture used to manufacture control horns from brass strip and DuBro wheel-collars.
This shot demonstrates why the need for a bow plane operating shaft yoke: to jump over the installed WTC. Note the counter-weight mounted to the yoke -- its job to balance the heavy brass bow planes; without the counter-weight the servo and linkage would have been subjected to an excessive back force when working in the 'dive' direction. Note the control horn on the port operating shaft that makes up to a pushrod that connects back aft of the WTC to the bow plane servo pushrod.
The after end of the bow plane push rod terminates in a magnetic coupler which in turn makes up to a stiff piece of brass strip that engages the bow plane servo pushrod through two 1/16" inside diameter wheel-collars soldered to it, those collars making up to the wet side of the servo pushrod. You can just make out down deep within the bowels of the HUNLEY models hull how those wheel-collars make up to the servo pushrod projecting from the after end of the WTC.
Well, time has once again come to assemble yet another 1/96 SKIPJACK. This one to replace a unit I gave away to a good friend. The current build has been on the wall, about 80% complete, for three years. But, now that I'm retired -- and need a break from the HUNLEY project, which was giving me a dose of the dreaded, 'builder's block' -- I have the time to complete this thing and add it to the fleet being readied for next years regatta circuit. So, the other day I yanked it down to work-table altitude and got to work on completing the paint-job.
Everything was done but for the oil-canning effects, non-skid over the deck and sail planes, markings, and weathering. Here I'm preparing the parts that evidence dishing-in of the external plating: the stern planes, horizontal stabilizers, bow planes, sail, and rudders.
Here are some of the photos and drawings I've gathered that outline placement of the oil-canning on the various structures. The task involves masking tape and off-color variations of the two fundamental colors: dark-dark gray and anti-foul red. Either darkened or lightened colors are shot within or obliquely to the unmasked portions of a structure. More on that later as I progress.
Work starts by cutting narrow strips of low-tack masking tape. The raw tape is stuck to a sheet of Sentra (brand name for a foam-core PVC plastic sheet favored by model-builders) which is firm enough not to warp under the pressure of the knife, but soft enough not to dull the tip of the blade as I make the cuts.
In foreground you see how the strips are used to define the 'high' points of internal structures, the stringers and frames which give a structure strength. It's between these high points that sheet metal eventually sags giving things that oil-can look. On the model such representation is a painting cheat: to give the illusion of physical distortion of the surface, where in actuality, its just shades of base color.
The following shots show what I'm going to shoot between the masking tape strips -- those strips representing stringers and frames. I'm jumping ahead to show the finished work on one of my 1/72 SKIPJACK models. On this shot you see the oil-canning on the submarines sail.
Air-brushing the off-color anti-foul red on the faces of the horizontal stabilizers.
... and the masking removed.
Initially the oil-canning effect is too stark but is later toned down with a misting of the base color give only a suggestion of deformed plate.
On real submarines the areas of deck (and sail planes in this case) that get foot traffic receive a coating of a very course, crushed rock-binding resin paint called 'non-skid'. The rough texture of this 'non-skid' paint, though almost always over-painted with hull black, tends to bounce light in a way that at almost any angle the non-skid portions of hull appear to be a shade lighter than the surrounding black.
And that's the off-shade of the hull black used to represent the non-skid areas on a model. Below is a shot of the non-skid dark gray applied to both the upper deck of the submarine as well as the top portions of the sail mounted fairwater planes.
As future work to weather the model will require re-masking of the non-skid areas, the specially cut masks used to achieve the demarcation lines between hull black (actually a very, very, very dark gray) and non-skid gray will be needed later, so they are preserved on this scrap piece of Sentra sheet.
Clear plastic sheet stencils (being clear its a simple matter of tracing their outlines over a scale plan-view of the subject) were cut to shape. These stencils would guide my knife as I cut the low-tack masking tape counter-mask and mask proper used to define the line between non-skid and black. The counter mask elements were further divided longitudinally into halves, this done so I could place them dead-center atop the deck. The purpose of the centered counter-masks is to guide me as I butt the edges of the mask proper elements up against the outboard edge of the counter-masks. This method insures symmetry of the masked outlines.
For clarity I've pulled the masks back a bit from the counter-masks so you can more easily see that one set of masks is the mirror of the other. Of course, after this shot was taken, I relocated the masks up tight against the counter-masks. You can just make out the deck and fairwater plane clear stencils bottom, left.
With the outboard masks butted up against the counter-masks all I had to do was remove the counter-masks -- taking care to save them for later use -- leaving those portions of deck that will get the non-skid gray exposed.
I've still got to mask out those portions of the aft 'international orange' marker-buoy, the top of the safety track, as well as the circular seating surfaces around the forward and after escape trunk McCann rescue bell/DSRV seating surfaces.
The circular masks were cut out of masking tape with simple circular punches. These are made from brass tube that have had an end beveled in and out to produce a knife-edge. Simply press the tool into the tape and, like a cookie-cutter, the tool produces a perfect round mask and counter-mask.
All masking in place I mixed up a slightly grayer version of the hull black. These days I use that cheap-ass Walmart water-soluble acrylic paint (a lot cheaper than that outrageously expensive crap you get from the hobby shop) for this kind of work. It's easy to prepare, is very easy to clean the brushes and air-brush after use, and dries almost immediately when pushed a bit with a hot-air gun. In this shot you'll note that I've added more pieces of masking tape to ward against any over-spray from getting to places I don't want it. Tape is cheap, fixing over-spray mistakes is aggravating!
Laying down the anti-skid gray.
Masking removed and saved for later use. The non-skid and black areas of hull are now ready for weathering. More on that later.
Well, time has once again come to assemble yet another 1/96 SKIPJACK. This one to replace a unit I gave away to a good friend. The current build has been on the wall, about 80% complete, for three years. But, now that I'm retired -- and need a break from the HUNLEY project, which was giving me a dose of the dreaded, 'builder's block' -- I have the time to complete this thing and add it to the fleet being readied for next years regatta circuit. So, the other day I yanked it down to work-table altitude and got to work on completing the paint-job.
Everything was done but for the oil-canning effects, non-skid over the deck and sail planes, markings, and weathering. Here I'm preparing the parts that evidence dishing-in of the external plating: the stern planes, horizontal stabilizers, bow planes, sail, and rudders.
Here are some of the photos and drawings I've gathered that outline placement of the oil-canning on the various structures. The task involves masking tape and off-color variations of the two fundamental colors: dark-dark gray and anti-foul red. Either darkened or lightened colors are shot within or obliquely to the unmasked portions of a structure. More on that later as I progress.
Work starts by cutting narrow strips of low-tack masking tape. The raw tape is stuck to a sheet of Sentra (brand name for a foam-core PVC plastic sheet favored by model-builders) which is firm enough not to warp under the pressure of the knife, but soft enough not to dull the tip of the blade as I make the cuts.
In foreground you see how the strips are used to define the 'high' points of internal structures, the stringers and frames which give a structure strength. It's between these high points that sheet metal eventually sags giving things that oil-can look. On the model such representation is a painting cheat: to give the illusion of physical distortion of the surface, where in actuality, its just shades of base color.
The following shots show what I'm going to shoot between the masking tape strips -- those strips representing stringers and frames. I'm jumping ahead to show the finished work on one of my 1/72 SKIPJACK models. On this shot you see the oil-canning on the submarines sail.
Air-brushing the off-color anti-foul red on the faces of the horizontal stabilizers.
... and the masking removed.
Initially the oil-canning effect is too stark but is later toned down with a misting of the base color give only a suggestion of deformed plate.
With the deck and sail plane non-skid gray applied, the two remaining tasks were to represent the slight metal plate dishing of the control surfaces and horizontal stabilizers (the dishing of the sail would come later), and scuffing of the non-skid surfaces by foot traffic.
The dishing, sometimes referred to as 'oil-canning' on the real thing, is due to the elasticity of steel plate (everything is elastic to one extent or another) which will, over time, dip inward slightly against the rigid under-structure of frames, ribs, bulkheads, strings and other such foundations upon which the plating is secured.
Light reaches our eyes when looking at such structures will change in color slightly from the convex-concave variances produced by the slight dishing of plate between under-structures. A model makers cheat is to vary, every so slightly, the color between the supposed high and low portions of the plating by tinting the base color ever so slightly and shooting it over the surface upon which narrow masking strips are placed, those strips over where the under-structure would meet the plating. The below shot illustrates the desired result: the suggestion of oil-canning.
A process to represent actual plate distortion... and advocated by the criminally insane... is to mask the high points and sand-blast within the masking. Works only if the entire structure is of one type substrate.
A rather grizzly fact: The source I used to find the pattern of such oil-canning on the SKIPJACK was examination of the relevant pictures of the sunken SCORPION The Mystery of the Sinking of the USS Scorpion (warhistoryonline.com) . All was revealed when that boat imploded: tremendous pressure pulses were created that physically distorted the plating to an extreme extent. See: 'explosive metal forming' Microsoft PowerPoint - explosive forming.pptx (hermeticsolutions.com). Anyway, that's how I worked out the pattern of dishing for the horizontal stabilizers, stern planes and rudders. I juxtaposed the layout for the sail planes to those of the stern planes.
DuPont ChromaColor two-part, polyurethane automotive paint was used to achieve the base colors of dark, dark gray for the upper hull, sail planes, portion of the upper rudder, and sail; and the anti-foul red of the hull, horizontal stabilizers, rudders and stern planes. This system is a very tough chemical, UV, and abrasion resistant coating. Has to be. Its auto paint... duh! The only liability about this stuff is the care I have to take when cleaning the tools after a painting session as this stuff cures exothermically, and if I don't jump right on it after spraying I'll loose my precious spray-brush/gun. Unfortunately this wonderful stuff is no longer available. Rule of thumb: the more toxic it is, the better job it does of sticking and warding off damage.
(Now, god help us, the EPA, OSHA, and other goose-stepping federal and State agencies have foisted water-soluble paints on the automotive industry! I've lived too long -- thanks to California and the other tree-hugers, the good coating systems are no longer commercially available).
Anyway...
For the detail painting and weathering work I go to a more user friendly chemistry such as water-soluble acrylic paint, artist's oils, pastel chalks, colored pencils, and soft artist crayons, to name just a few of the agents I'll employ to give the model that 'used' look. These are not durable agents, but after their application the entire model will be give a protective ChromaClear coat that will be flattened down considerably to give the presentation the proper, uniform sheen.
You see here the mask marking stencils (for masking the non-skid areas of hull and sail planes); cutting board where strips of masking tape are cut to length; the ever reliable Paasche model-H air-brush; and a selection of base colors and tints of them needed to achieve the oil-canning effect.
The process for the appendages -- different for the sail, which will get it's own chapter -- is to cut out very narrow strips of low-tack masking tape and apply them across the face of an appendage, following the documentation that denotes the high points of the plating.
Then, as near the center of each 'square' as possible I gently blasted on a spot of toned down base color. In this case the anti-foul red. Here I've already done the rudders, and stern planes. And I just started
to remove the masking from the starboard horizontal stabilizer.
I'm using my ancient Paasche spray-brush with the #1 tip. Just right for this kind of work. Air pressure was dialed down to about ten-psi. As long as possible during the build I keep the control surface operating shafts 'wild', i.e. they can be removed easily. This so I can make use of a special handle which gives me the ability to move the work in relation to the spray-brush with ease.
In the previous chapter I temporarily removed the deck non-skid masking to show off the work. Here I'm reinstalling it. An easy task; all I had to do was follow the painted on demarcation line between the lighter toned non-skid and the dark, dark gray hull, placing the inboard edge of the mask pieces right on the line. This in preparation to stippling on scuff-marks put there by people walking atop the hull and sail planes. A pristine model looks like a toy. One properly beat up and weathered looks real.
The non-skid gray was toned down with more white to stand out when stippled onto the surface of the hull and sail plane non-skid portions. At this point the scuffing is too distinctive and will be toned down in a few moments.
Notice the ragged ends of this poor paint-brush. It was selected for this stippling job just for the randomly splayed out brush hairs. A suitable stenciling brush. It is loaded with paint, which is then wiped out as best I can on a rage (to the right). There is some residual paint in the brush and that's all I need to get it on the model parts. No strokes of the brush, just gentle stabbing onto the work, the brush held at a right-angle to the work.
The over-stated scuff-marks were over-coated with a light misting of the base dark, dark gray to tone things down to an acceptable level. The same was done to the none-skid scuff-marks atop the sail planes.
This coming fall the North Carolina Model Boat Club will again host the annual 'Fleet-Run'. An all 1/96 scale r/c boat (and submarine) group run at City Lake in the city of Rocky Mount. I've attended one of these events and it's a wonderful three days of running at one of the best boating venues on the East coast. Currently I'm just about the only guy who operates r/c submarines over there. However, next year I will be joined by J. Hoffman who will operate a German Type-21 U-boat. This guy is renowned for his very well crafted, scratch-built model warships, and its a pleasant and instructive task to study his work in and out of the water.
I'm a submarine guy. Mr. Hoffman want's to be a submarine guy. So, we agreed to a collaborative effort: he wanted a German Type-21 submarine to add to his 1/96 fleet, and I agreed to help him equip it with the gear needed to make it a fully functional r/c submarine.
And here it is, in foreground, next to my still in-work 1/96 SKIPJACK. Remarkably, they are both just about the same length.
The entire model kit was fabricated in a printer, I don't know at this time if it was a filament or resin type printer. You see that blue tape on the sides? That's to hold the three pieces of hull together for these shots. I assume it was printed this way owing to the machines maximum height build-up ability. Anyway, I will eventually glue the three hull pieces into one, then, at the waterline, I'll split most of the upper hull from the lower hull. This will give us access to the interior for installation of the water tight cylinder (WTC) that will contain the control, ballast, and propulsion sub-systems needed to animate the model.
Though only some 31" long, the hull has room for a 2" diameter WTC with all the gizmos needed to permit control of the propulsion, stern planes, rudder, bow planes, and ballast sub-systems. I've yet to determine how much water the ballast tank has to hold, so I'm deferring assembling the WTC till I have that number in hand, which will drive the length of the WTC's centrally located ballast tank.
Most Allied nations, after the war, conducted evaluation of the surviving 21's. Those submarines, the most advanced production submarine of the war became the grand-daddies of the first post-war designs to join the cold-war. Quit a legacy! There's a little 21 DNA in the SKIPJACK's. Both true underwater fighters.
To make things easy I elected to work out the propulsion shafting and bearings; rudder operating shaft and control horn; and stern plane operating shaft and control horn with the after section of the hull removed from the rest of the hull. In this shot I've already made up the propellers -- I was surprised and delighted at the strength of these and the other thin cross-section printed parts -- to 1/16" diameter brass propeller shafts, and installed them into the stern tubes embedded at the trailing edges of the horizontal stabilizers.
There were no bore holes in the propeller hubs, and that meant some careful work starting and finishing off interference-fit bores for the 1/16" diameter brass rod propeller shafts. The bores started life as a punch-mark, then a shallow plunge with a #80 bit, followed by a reaming with a hand-twisted #53. At that point the bore was only 1/32" deep, a good enough pilot-hole to let me use the big gun with an assurance that the bit would not wander off-center.
On the drill press, with the hub tip residing in a hole drilled into a scrap piece of shelving board laid atop the machines bed. This way the three blades of the propeller rest atop the board and in so doing presented the hubs base at a right-angle to the drill-presses 1/16" bit. Then -- with very light, shallow stabs of the bit into the work -- I deepened the hub bore hole. Sweat-pumps to Fast!
Damn! I didn't break anything. Notify the Media! Wrench-wrist Dave pulls another one out of the hat!
Just some of the tools used to hand-bore the pilot-holes into the propeller hubs. The same tools were used to bore out the propeller shaft stern tube bores -- I was glad to find that even the horizontal stabilizers were hollow, and of very thin section, which made that job a cinch.
A nasty characteristic of the 21's was that differential use of the screws to aid in the turn was backwards from most vessels. This is because the thrust line of these toed-in shafts intersects the crafts longitudinal center a bit aft of the vessels center of mass. But, since this model will have these two propellers spinning at identical RPM, in counter-rotation to one another, that's not an issue for this model. Here I'm sliding a propeller shaft into its stern tube.
Now, to work out the rudder and stern plane linkages. God help me!
Thank you, sir. The kit was provided by Joe Hoffman, and he 3D printed the thing (I believe using the resin bath process). If you wish I'll ask him if the file is available.
The hard part will be getting all the control surface operating shaft linkage elements within the stern and not resorting to external horns and pushrods. We'll see.
The oil-canning effect applied to the sail. An involved process as it entails multiple applications of strips of masking tape, each piece evenly spaced and applied to right angles to one another. The end result is a checker-board pattern of squares, each with a small feather of light gray in the lower, after corner -- the lighter gray against the dark dark gray suggesting the light source (sun) to be ahead of the subject, denoting late morning, or early afternoon.
The strips of tape are laid down in checker-board fashion. It will take several cycles of lay-down of these strips to get the full array of plating with the phony, painted on, oil-canning. Note the drawing used as reference --used to guide me as I determined strip width and placement on the sail.
If you will, the direction of the imagined light source is pointed to by the after tip of the Paasche air-brush used to apply the lightened color to the lower, after corner of each exposed 'square'. Know that only one-quarter of the dished in panels have been represented. The masking will have to be shifted three more times to get them all.
After the first pass, the masking is removed -- and saved. Then, using the faint variance between dark dark gray and the lighter gray I re-applied the masks to get the second set of squares painted.
And the last round of strip shifting followed by a corner squirt of paint, and the sail oil-canning is done. Inevitably the work is over-done, but will be toned down later with a careful, well cut mist coating the the dark dark gray till things take on a more realistic look.
Wrapping narrow strips of tape radially around the diesel exhaust line fairing. I used a discarded strip of tape (sized in width to produce the checker-board sail pattern of the sail) to insure correct spacing between the narrow strips of masking. I've seen no evidence of oil-canning on this fairing, but sometimes, when I get into a weathering task I lose all self control. Anyway... it looks nice... screw it... sue me!
The lightened gray was shot between the narrow strips of masking tape. That done, the masking was removed.
A fiber-glass bristle 'correction pencil' was used to scrub away the light gray to achieve the look of slight dishing.
As a practical matter all the hand-hole access points, doors, dead lights, air-induction grating, emergency stern light, and other flush-mounted items on the sides of the sail do not have stringers or frames under them. So, those items are not subject to the distortion, as does the surrounding plating, that gives us the oil-canning look. Those items (with the exception of the dead lights, induction grating, and emergency stern light which later get an even lighter shade of gray) are addressed with the dark dark gray of the hull.
This masking around those items looks like a tedious and exacting task doesn't it?... and it was totally unnecessary! If was not such a dumb-ass at the beginning of the sail weathering job I would have masked these areas themselves before going through the above oil-canning process -- which would have been so, so much easier. One step forward, one step back. Duh!
Stepping back a bit to a previous picture. In the last thrilling, action packed, hair-raising installment I masked off those portions of the sail where oil-canning would not be evidenced. So, I applied the masking needed to paint the doors and other items the hull dark dark gray. Note the use of circular brass tube punches to cut discs out of masking tape. Very useful tools.
Here's the raw oil-canning (not yet toned down) with the hand-hole access plates, doors and other stuff painted the dark dark gray and all masking removed. This is near the end-game of sail weathering before the toning down process.
laying down the dark dark gray paint within the masks. Removed here for clarity is the use of post-it notes to provide shielding from over-spray as I shot paint onto the non-oil-canned portions of the sail.
Removing the masking.
One more shade of gray, a very light one, will be applied to the dead lights and emergency stern light lens. But, first, all that crass oil-canning work had to be toned down with careful mist coating of the entire sail structures with the dark dark gray. In this shot you have to squint real hard to make out the oil-canning -- and that's as it should be: weathering is at its best when it complements a display but does not distract from it. As they say: less is more.
And, finally, the dead lights and emergency stern light lens are masked off and painted a light shade of gray, representing transparent structures. Post-it notes make for good, broad coverage masking elements -- their low-tack edge sticks to the work fine, but not to any degree of 'stick' that will damage the paint upon removal.
At this point all that fragile acrylic paint work was protected with a heavy clear coat of ChromaClear. That product seen in the larger containers in background. Note the use of hemostat, handles, and machine vices to hold the smaller items as they sit under two infra-red lamps, those heat-sources used to accelerate the cure of the clear-coat.
Enough SKIPJACK work. I'm sick of it! Moving on to that neat little 1/96 Type-21 project.
Picture 1 had me wondering how you were ever going to fit in all the electrical gubbins. Then, after all the mucking about along the waterline, came the circular saw and hand saw. Behold, indeed. Ace!
Picture 1 had me wondering how you were ever going to fit in all the electrical gubbins. Then, after all the mucking about along the waterline, came the circular saw and hand saw. Behold, indeed. Ace!
Three days after splitting the top from the bottom of the 1/96 3D printed Type-21 hull I find both halves warped significantly, radially and longitudinally. FUBAR!
I've seen phenomenon like this with round and box cross-sectioned extruded tube stock. Seems the manufacturing process, with the unequal temperature dissipation after extrusion, causes internal stress that only relieves itself once the structure is split longitudinally.
Any Material Engineers want to jump in here? Thoughts? Suggestions? Accusing finger pointing in my general direction?...
Anyway, the model is ruined, dead Jim, tits up, wasted, useless...
Here's the plan: get another three-piece Type-21 off the darned machine, just like this poor thing cluttering up my shop (and for god's sake, this time make it at least a .070" wall). I'll glue the sections together as before. But, this time, I make a proper glove-mother mold from which to produce proper GRP hulls -- as Nature, in her infinit wisdom, would have it. Not this good-time-Charlie, quick, no-brains-involved robot Replicator crap.
Interesting information on possible limitations of 3D printed parts. Internal stresses (or other anisotropic properties) could be particularly severe in metal parts, or even used to some advantage given enough control over the manufacturing process and implementation. Making a mold off of a printed form is also going to be something of an experiment (stresses and thermal effects there as well?); another potential route would of course be to print the top and the bottom separately to begin with.
The HUNLEY is finally at that point where I can address some of the broken detail items and prepare the model parts for paint. Here I'm soldering together the broken off forward 'cut-water' that sat just forward of the forward access hatch/conning station.
Before any filler, putty, or priming the entire model was scrubbed with a mild hydrocarbon solvent to free the surfaces of any oil or other contaminants that would otherwise inhibit adhesion of the above mediums.
All raw metal parts that were to later receive primer and paint were first pickled with Ferric chloride acid, rinsed in fresh water spiked with a bit of baking soda, then thoroughly dried.
Where needed air-dry touch-up putty was applied and later wet sanded smooth.
Though no longer commercially engaged in the sale of water tight cylinders (WTC), I do have a wall full of uncompleted models that will eventually need a cylinder to make them operational. I recently sat down and banged out ten single-shaft WTC's for those upcoming projects.
The motor-bulkheads are two-piece, cast resin units that contain a 3:1 gear reduction; three water tight seals for 1/16" diameter pushrods; a 3/16" output shaft with water tight seal; antenna lug; pass-through nipples for ballast induction and discharge air; and an equalization valve.
Attached to the dry side of the motor-bulkhead is an aluminum and resin device tray and bulkhead upon which will be placed the servos, receiver, low pressure blower, angle-keeper and other devices needed to make the model submarine operational.
Sheet-metal work on display. Here I'm using templates to lay-out the aluminum parts.
Once the aluminum parts are cut to outline they are bent to shape in this poor-man's break I use for thin gauge metal work.
The metal-to-metal attachments are made with pop-rivets.
WTC's awaiting assembly. As I near completion of a model I will select a cylinder of the desired length and take it to completion, populate it with the devices and battery needed, and get that model operational. That's the plan... if the creek don't rise, that is.
Casey Thrower and I, though only physically meeting one another recently at the 2021 SubFest event in Georgia last Summer, have been in this game together for the better part of a quarter-century; we've been kicking around ideas and projects all that time. At the event he drove some of my boats -- and in no time he became infatuated with the easy handling and speed of my little Small Worlds Models, 1/96 BLUEBACK. By time the three-day event was over, and we all started packing our stuff for trips back to our respective homes, I agreed to help Casey get his own BLUEBACK up and running in time for the upcoming 2022 regatta season.
Below is pictured my BLUEBACK at the 2019 Groton Sub-Base fun-run. For video of this and other models in and out of the water I strongly recommend you look over the 2021 SubFest video.
The next few chapters chronicle the work I have done and will do to provide my friend with an assembled, outfitted, and tested WTC for his own BLUEBACK. Included will be a discussion on my partial assembly of a BLUBACK hull kit and integration of Casey's WTC within it. This shot illustrates what it takes to turn a nice fiberglass, resin, and metal kit into a practical, well running r/c submarine: The hull kit itself -- now offered by The Nautilus Drydocks -- and a suitable WTC, under development, but soon available from the same source.
The term, 'static' denotes the mode of operation of the model submarine; this type, like the real thing, takes on an amount of ballast water whose weight counters the buoyant force of the above waterline portions of submarine when they become immersed.
This differentiates the 'Dynamic' type boats from the 'Static' type. The dynamically diving boat can only slip beneath the surface by plowing under at speed; relying on the dynamic force of the hull and appendages to force the always positively bouyant submarine beneath the surface -- not at all scale like. But, good enough if you are OK with toy-like performance. Yes, I'm a snob. Sue me!
I took this shot yesterday. I had just taken delivery of the BLUEBACK hull kit and box of devices that were dropped shipped to me from the Nautilus Drydocks Remote control submarines | The Nautilus Drydocks (rc-submarine.com) on behalf of my partner in crime, Casey Thrower. It only took me a days work to assemble his WTC. I'll spend the weekend populating it with the servos, receiver, angle-keeper, BEC, ESC, fail-safe, battery, mission-switch and other goodies to make it an operational system.
You get an idea here of what a tight fit the 2.5-inch diameter WTC is to the 1/96 BLUEBACK model.
Remember all those WTC's I put together in the ruff? One of those was pressed into service as Casey's BLUEBACK WTC.
Here is the victim, showing off the internal bulkheads, forward bulkhead (removable to access the battery space), and the after removable motor-bulkhead with attached aluminum device tray, mounting bulkhead and resin servo foundation.
OK. Let's stick this sucker together into a coherent whole, shall we?
Though retired I still have bins full of excess parts Ellie and I manufactured while operating under the D&E Miniatures banner. My recent retirement was not planned and occurred with the parts bins nearly full. The result is a shop and two sheds teaming with sub-assemblies, jigs, fixtures, rubber tools, sheet-metal, brass stock, resin, templates, and cylinder stock. Everything needed was at hand.
First task was to employ the 2.5" marking templates to identify where to drill holes for the vent valve, internal bulkhead mounting screws, emergency gas bottle neck, flood-drain holes, external manifold ports, and where to cut away the not needed length of cylinder.
The raw circular edge of the cylinder was trued up on a belt-sander equipped with a specially made fence that holds the work perpendicular to the machines bed -- this is how I face of the cylinder ends. Easy peazy.
Lexan cuts like hard cheese. That property of polycarbonate plastic makes chamfering an easy task best accomplished with a knife. Lexan is also very forgiving of shock and stress and will not crack as readily as acrylic plastics.
A spray coating of oil within the cylinder eases insertion of an internal bulkhead as it's pushed into position.
And that's exactly what I'm doing here: pushing in the second of the two internal bulkheads that separate the three spaces within the cylinder. The central one being the ballast tank. Note the use of Teflon 'plumbers tape' to tighten up the O-ring seal between bulkhead and cylinder. Once an internal bulkhead is positioned, holes are drilled through the cylinder to match threaded holes in the foundation nibs of a bulkhead so it can be secured in place with flat-head machine screws.
The internal bulkheads in place I then populate the ballast tank with the vent valve bell-crank, pivot-pin, emergency gas bottle and blow-valve, brass tube conduit, and external manifold that will route induction and discharge air from the low pressure blower (LPB) from the after dry space to the ballast tank.
Your typical r/c model submarine WTC is a system comprising control, ballast, and propulsion sub-systems; everything needed to manage the model submarine in a scale like manner.
Here is the basic WTC -- already outfitted with most of the ballast, and propulsion sub-systems -- ready to accept the devices needed to bring it to life. I so loath this part of the job!! Electron chasing is not my idea of fun.
It's good practice to first validate correct operation of all devices off WTC. Better to trouble shoot with elbow room than to fish around in the tight confines of a cylinder.
First task was to break out the r/c system Casey sent me and check it out. Good old, rock-solid Futaba gear. I love 'em. That done I was now in a position to set up the devices that interface with the servos and transmitter (through the receiver) and check them for correct operation.
But, not now. I'm not in the mood! Drank too much coffee today -- system integration often leads me to screams and throwing shit through windows. Not today, no way!
I instead elected to play with the BLUEBACK's tail-feathers; get them and the sail mounted fairwater planes working properly.
I want to make it clear, up front, that the kit I was offered by Nautilus Drydocks could be one that had a few production flaws (they would discount me a considerable amount for those shortcomings) or a pristine kit.
Cheap bastard that I am, I swung for the discounted kit. Upon inspection of the arrived kit the only real issues were some voids in a few of the cast resin pieces. The GRP and metal parts were perfect. So, I spent most of the day working the control surfaces and their adjacent structures.
Initially I ground away at some flash and sprue nubs with moto-tool and hand files.
The resin part voids were filled with CA and baking soda grout. Once those masses had hardened (very quickly, I might add) I got things back to contour with files and sanding block.
These special round-gouges were used to chase out flash from the stern plane leading edge channels built into the trailing edges of the horizontal stabilizers.
I bored out a 1/4-inch diameter hole to accept the propeller shaft Oilite bearing.
All resin pieces were then soaked with lacquer thinner and scrubbed wet with an abrasive pad. This to remove all oils and other contaminates that would otherwise interfere with proper adhesion of later applied adhesives, putties, fillers, primers and paint.
Operating shafts were made up to the stern planes, rudders, and fairwater planes. The control surfaces were then test fit to their respective connective pieces: yokes for the stern planes and rudders, and a magnetic bell-crank for the fairwater planes.
Here you see how the linkage to the fairwater planes ('sail planes' in this shot) is made up -- a simple set of magnets. Easy to install. And little back-lash.
And a check-fit of the control surfaces to the tail-cone and sail.
Tomorrow, back to work on getting the WTC operational.
Sniveling coward me decided not to do battle with the WTC electronics today. Instead electing to continue work getting the hull pieces to fit together.
Pictured is the end-game: an assembled tail-cone permanently bonded to the rear of the lower hull. A second BLUEBACK hull was in work at that time, and its lower hull, this time showing off the radial flange at the bow with its weird curvature -- actually a very clever move by the kits designer, Dave Manley. That curve follows the 'banjo line' of the lower sonar dome window, which neatly fits the slight gap between the radial break between upper and lower bow sections.
The two GRP hull halves split longitudinally at centerline. The lower hull half has a recessed longitudinal flange over which the upper hull slips over. But, this is not a perfect world, and just the single flange will do nothing to keep the upper hull half from springing out, spoiling an otherwise neat, well hidden separation line between hull halves. That's why I developed these little resin 'capture lips'. Secured within the upper hull they press the inboard side of the lower hull longitudinal flange up tights against the inside of the upper hull, insuring proper registration at the split between hull halves.
An artifact of some GRP hard-shell tools are conical waste pieces at both ends of a tapered hull. These were removed with the aid of a carbide cut-off wheel.
Most of the lower hull bow fairing was removed, leaving a 1/4-inch radial flange. Marked off here with the aid of a drafting compass equipped with a Sharpie marking pen. This flange, captured under the upper hull bow piece, would lock the forward end of the two hulls together when assembled.
(A single machine screw at the stern will hold the upper hull down tight on the tail-cone, and is all it will take to hold the assembled hull halves together).
Hand laid-up fiberglass structures, if great care is not taken to wick out excess resin from the glass weave, tend to vary in wall thickness -- because of gravity, excess resin will pool and produce hull pieces thick and heavy at the bottom of the lower hull and thick and heavy at the top of the upper hull. This excess material has to be ground away at the stern and bow to get the tail cone radial flange to fit properly when installed at the stern of the lower (and later upper) hull.
The wall thickness at the stern of the two hull halves, even after grinding, was a bit thicker than would be accommodated by the stern-cones radial flange, I found it necessary to turn the flange down about .050-inch using my handy-dandy-wonder Taig lathe. A neat attachment to this machine is a tapering tool-holder that can be set to the desired angle, and used to turn the correct taper angle, and do it with great precision.
The kit provided a blank with all the capture lips needed to hold the hull halves tightly together when assembled. All I had to do was break each one free with the aid of a razor saw and a bit of force. The upper hull was prepared by marking where each capture lip would go and roughing up the fiberglass surface with grinder and a sanding stick. The lips were then CA'ed in place.
The assembled hull is now nice and tight, but will need a lot of block sanding and filler to make the radial and longitudinal seams almost go away. And I'm just about ready to bond the tail cone to the lower hull. Tomorrow, maybe. Another reason to steer clear of the dreaded WTC outfitting!
Model building -- including its bastard step-child, kit assembly -- if done right is an exercise in proper planning and execution. You are tasked (often in the absence of coherent written and graphic instructions) to determine the material best suited for a given situation; optimum fabrication techniques; and to work out a rational assembly procedure. In short, establishing an overall methodology and chronology of tasks before lifting the first tool.
Here's the end-game: A long road from beginning to end, but a most rewarding trip if you do it right.
This step-by-step planning and execution regiment is personified in the tail-cone sub-assembly of this little 1/96 scale BLUEBACK r/c submarine model kit:
Where will cast resin, machined metal, cast metal, stock brass rod, and screw fasteners be best employed to achieve this component dense sub-assembly -- an assembly amicable to easy access or removal for later adjustment or replacement? How to engineer the linkages and running gear to work bind-free yet avoiding mechanical interference with other mechanisms sharing the tight confines of the tail-cones interior? And in what order are the manufacturing and assembly tasks most efficiently performed?
Chronology of tasks (the sequence of events) is a vital consideration: Fabrication and/or assembly of part-A to part-B is done and verified correct before addition of part-C. Proper planning, establishment of a rational methodology and chronology is key to streamlined and enjoyable model work.
It's all about avoidance of putting the cart ahead of the horse, or making the cart from the wrong stuff.
You'll notice that I have not yet attached the tail-cone sub-assembly to the lower hull. That's because it's much easier to handle this small, complicated item off-hull till all the inner workings have been installed and tested -- only then will the tail-cone be joined to the hull. And that general rule holds for most other sub-assemblies.
This is a kit. Every part needed should have already been at hand. But, no propeller... Shit! The other elements of the running gear -- propeller shaft, universal coupler, thrust washers, Oilite bearings -- were installed, but the sub-assembly was not complete.
Fortunately I still had in the shop one of my metal casting tools for 1/96th scale BARBLE class propellers. So, I made one. With that done, the propeller in place, and everything working in concert, I could confidently proceed with attachment of the tail-cone to the lower hull.
I find white-metal to be an ideal medium when the situation calls for reasonable strength from low wall thickness structures. It is also a medium that is easily machined by boring, threading, and worked with common hand-tools. When pickled properly this metal alloy will bond well with adhesives, fillers, and primer.
While I was set up for gravity pouring of molten metal I also worked up a few propellers for a 1/35th Type-23 model I'll be working on next year. You see the two rubber tools here. Note that the BLUBACK propeller tool has, as an element of the upper half of the tool, a long neck. This has running through it an extended sprue channel through which the molten metal is introduced. The height of the sprue, the 'pressure head', through gravity, produces a significant force at the bottom of the tool. That force insures a quick and complete fill of the propeller cavities when the liquid metal is introduced.
The Type-23 propeller tool needed a removable length of brass tube to produce the needed pressure head that insured a complete fill.
And you can see what happens when you screw things up!
You change the temperature of a substance enough you change its state. Liquid, solid, gas, or plasma. Metal casting is simply taking a metal that is a stable solid at room temperature, raising its temperature till it changes state to a liquid, then pouring that liquid into a mold (tool) and allowing it to freeze back to the solid state. Nothing to it.
Note the long neck of the upper tool half. The higher the sprue channel, the more pressure exerted at the bottom -- where the cavities that give form to the propeller blades and hub are -- insuring a quick, complete fill of the tool during the pour.
I've already installed a stainless steel pin (core) in the lower tool half that will produce the 3/16-inch diameter propeller shaft bore centered in the hub of the eventual propeller casting. Here I'm placing weighted discs atop the tool to squeeze the halves together tightly, this to minimize flash. Gravity is our friend: it holds the tool halves together and, because of the metals high density, produces the pressure needed to jam the molten metal into the tools cavities.
Once the molten metal is poured, and before it has time to change state, I jam a wooden dowel into the sprue hole. This prevents the solidified pile of excess metal atop the tool from linking with the column of metal in the sprue, which would present an entrapment situation. Guess what motivated me to employ this trick?!
This drilling fixture is used to hold the propellers rotational axis perpendicular to the bit of the drill-press, no matter the angular displacement of the propellers hub to the bit. Once the hole is drilled it is tapped for a 4-40 set-screw (grub-screw for you European's) that secures the propeller to the propeller shaft. During this work the long sprue column is retained as it serves as a useful handle during the drilling and tapping operations. The excess sprue is sawed off once the set-screw is in place.
The last major machining operation on the cast metal screw is to spin it in the lathe as the 'dunce-cap' tapper is formed. Here I'm zeroing a length of shaft to the chuck with the aid of a dial-indicator.
The propeller is secured to the chuck retained shaft and the work is brought up to speed.
A tapper tool-holder is mounted atop the cross-slide and used to produce the conical tapper of the propellers dunce-cap.
Dad taught me shop-safety. It went like this:
MACHINES DON'T CARE
MACHINES CUT METAL AND FLESH WITH EQUAL ENTHUSIASM
The three propellers to the left show the three major stages of cast propeller fabrication: Casting; trimming, which includes removal of flash and provision of the securing set-screw; and dunce-cap shaping.
The propeller shaft is prevented from lateral or axial motion but free to spin within two Oilite bearings. The bearing at the stern steadies the shaft laterally and absorbs ahead thrust load. The bearing at the front of the tail-cone steadies the shaft laterally (and along with the stern bearing assures that the shaft falls along the boats longitudinal center-line) and absorbs the astern thrust load.
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