Scratch-built 1/96 Oscar II

[KevinMC]

With the carpenters glue now

With the carpenters glue now dry, I took the sail to a large disk sander to bring it to shape. This was done with the sail upside down on the sanding bed, using the 1/16" ply base as a guide for how much material to remove. I then put a tilt on the base for the sander and repeated the process, this time leaving a slightly beveled edge on the sail. A quick pass with a fine-grit paper loaded block sander, and here is the result]http://www.subcommittee.com/forum/new_sail_blocks_sanded.jpg[/img]



The next task was to radius the upper corner. I did this by eye last time, and spent an inordinate amount of time trying to get it "just right", which it still isn't. This time 'round I've decided to make a radius sanding tool to get the edge exact the whole way round. The tool itself is dead simple to make, and worked really well. (Moral here- It's definitely worth spending the time to make tools and jigs to accomplish even "simple" tasks.)

Step one was to make the "base" for the tool. It's nothing more than three pieces of lite-ply glued together to look like a corner-sanding tool. (This part of the tool was built in place, but first I placed a square of some plastic bag material underneath so I didn't inadvertently glue the tool to the sail as I was making it!)



Next for the radius- I found a piece of large diameter brass-tubing that looked like it would be just perfect for the job. I gave the tube a quick buff with some wax and PVA in preparation for use as a radius mold. Next I gooped some Icing into the corner of the radius tool, and sank the brass tube down into it.



Once the Icing kicked off the tube was removed leaving a perfectly round surface for creating the radius.





Almost done now- I 3M77'd a piece of 150 grit paper into the radius. Not so clearly visible, where the sanding paper isn't I placed some clear packing tape to help the tool to slide along the surface of the sail.



And to set the tool in action. The keenly observant will notice that this radius below looks a bit bigger than what's shown above. That's cause it is- When I completed sanding the radius the first time it looked a little too small, so I simply pulled up the sanding paper, found a slightly larger diameter form (this time it was a small diameter aerosol can) and molded the new radius into the same tool. Here's the result:




And here is a glamour shot of the new sail in it's place...

[anonymous]

Perfect. I'm glad to see

Perfect. I'm glad to see I'm not the only one that works with balsa.

Very nice Kevin!

Steve

[KevinMC]

Steve- Thanks. I've been told

Steve- Thanks. I've been told that I need to "get into the 21st century" and "stop using that antiquated building material!" But being an airplane guy I already have large quantities of balsa in all shapes and sizes. It's easy to cut and easy to shape. I just hate it when it acts like a sponge while I'm wet sanding!

[boss subfixer]

Kevin,
This one heck of a

Kevin,
This one heck of a how to! I already have a binder ready so I can print this for reference, with your permission of course. keep up the great work.
P.S. I especially appreciate the "this is a mistake I made and how I fixed it" parts.
Don

[gerwalk]

P.S. I especially appreciate the

P.S. I especially appreciate the "this is a mistake I made and how I fixed it" parts.
Don

[color=#000000]Don]

[KevinMC]

Don- By all means print

Don- By all means print it off, but you certianly don't need my permission!

I must admit it was tough the first time to say "Uhh, hey guys I screwed up." But making mistakes does seem to be such a natural part of the hobby, and there's no doubt that you'll never learn more than by watching someone else's mistakes...

[boss subfixer]

Kevin,
Even though this is a

Kevin,
Even though this is a public forum I still respect others work as soley theirs, and even though it may be or seem implied I was brought up to ask.
Don

[KevinMC]

Don- Your courtesy is both

Don- Your courtesy is both noted, and appreciated. Thank you sir.

Allright, I've pulled the sail from the vac-bag and cleaned it up. There was some minor pinholing in the glass so I painted on another layer of epoxy, gave a light sand and hit it with the primer. Here's the result in place on the hull.





The sail has a bit of a rock to it sitting on the curved upper surface of the hull so I decided to correct the fit. I did this by running a bead of Icing on the underside of the sail and "squishing" it into place. I don't want to make a mess of my unfinished master though so here's another trick worth remembering (if you've not seen it already): I used a couple of strips of packing tape as a release surface to mold against. I gave the tape a quick wipe down with some PVA to ensure that the Icing would break away more easily, and with that I had a perfectly smooth surface to mold against that matches the upper contour of my hull exactly.



Next I mixed up some Icing and smeared it in a thin bead around the periphery on the bottom of the sail. Then line it up and quickly push it into place. I used one of my ballast weights (Not that kind of ballast Art! ) to ensure that the sail stayed completely seated on the top of the hull while the Icing kicked off.



Once cured to a jelly-state, use a sharp hobby knife and trim away the excess Icing that oozed out from underneath the sail.





The last thing to do once the Icing has completely cured up is to break the sail free from the hull. Be advised that this took a good strong (but careful) whack with the heel of my hand. Here's an "after" shot of the underside of the sail to show how far in from the edge the Icing oozed.

[KevinMC]

Now it's time to mark

Now it's time to mark the panel lines on the sail. As with the hull (although I didn't actually mention this before) I've tried to separate the "major" features, like hatch openings, from "minor" features like anechoic tile breaks. I'll only be using panel tape on the major feature, any minor features I shoose to detail will be left until after the hull has been pulled from the mold.

Once again I'll be using 0.015" ChartPak tape for the panel lines. I generally start by marking the most significant features and work my way down to the itty-bitty things. On the sail, the first thing I marked was the Sierra escape module break lines, and then hatch for the COD EYE targetting system. The panel lines demarking the Sierra module are diagonal elements that start at the base of the sail and wrap up and over the top. The COD EYE hatch is predominantly rectangular and wraps down around the side of the sail, except for the side that is on top of the sail which is semi-circular. (As an aside, the COD EYE is a huge cylindrical antenna with a domed top. As best as I can tell it's primary function is to send mid-course targetting updates to the Granit cruise missiles once in flight.) To mask the arc I'd decided to use electrical tape again. Unfortunately as I started into doing this it was about 9]http://www.subcommittee.com/forum/icon_wink.gif[/img] ) a small block fo balsa, T-pin, a #11 X-acto blade. Yes, while growing up I watched alot of MacGyver! I started by jamming the blade into the balsa block until the tip was just peaking through the bottom. This would hold it securely and prevent it from wandering as I cut.



Next I pushed the T-pin into the bottom of the block spaced away from the blade by the radius of the arc. By starting from the bottom I could create a hole in the block to hold the pin and still precisely control where the pin exited on the bottom side of the block.



Last I removed the T-pin from the bottom of the block and re-inserted it into the block from the top. Presto! Instant compass.



I put the electical tape down on top of the sail and gave my compass a spin, and I'm pleased to say that it worked great. The second (uncut) piece of tape was put down to ensure that I could get the T-pin to seat where I wanted it.



My original plan for cutting the inner arc was to move the T-pin closer to the cutting blade by 0.015". After trying it out though I found it easier just to move the blade over a hair. This was done by trial and error, and it took me several tries to get it where I thought it was right. The other thing I found in doing this was that I didn't get the blade moved by exactly 0.015", it actually turned out to be closer to 0.020". Fortunately for me I also have some 0.020" ChartPak, so I used that to finish outlining the main part of the COD EYE hatch. (The other line to the left of the COD EYE is the aft break line for the Sierra escape module.)



The hatch also has a couple of visible "hinges" so I marked and cut these out as well. Notice that I've layed all the tape down first and cut all the pieces second. This ensures that the tops of the hinges are both in alignment. (Same procedure as shown when I marked similar features on the Granit doors.)

[KevinMC]

After much time on Saturday

After much time on Saturday morning, I finished marking all the hatches. Like with the COD EYE arc, I also marked the observation windows using elecrical tape. This was cut to height in a single strip, layed in place, and then I cut the individual windows in place. Again, following the process used on the hull, I'll leave off adding the raised features on the sail until after I've primed it up to the level of the tape.







Here's the sail getting loaded up with primer. Being a smallish part, I've glued a balsa "handle" to the bottom of the sail so I have something to hold on to while I prime it. This will just be broken off and trimmed up once the priming stage is complete.

[novagator]

Wow, she is looking beautiful.

Wow, she is looking beautiful.

[KevinMC]

Thanks John.

Well, things are starting

Thanks John.

Well, things are starting to slow up again and I seem to be accomplishing most of my work on the weekends. I have a bunch of photos to add, but I'm short of time so the annotations will be brief...

Having primered the sail I started adding the raised features. By far the most prominent feature on the Oscar sail is the hump that covers the Sierra escape module. Because of the way it intersects the top of the sail I wanted to build this as a separate assembly and then glue it into place. I made a f/g base to build the hump on to by placing packing tape on the top of the sail and laying several layers of f/g cloth down onto that. In the layers of cloth I also placed a paper template that I could use as a guide to ensure the hump covered the appropriate footprint on top of the sail.







To keep everything laying down flat I pulled a piece of clear plastic over the cloth and weighed it down. (I suppose this could be likened to a poor-man's vac-bag. )



And here's the result, ready to be built-up.



Now I've added Icing and contoured the upper surface to the shape I want. Notice the sharp angle at which the hump cleanly intersects the upper surface of the sail at- this would have been much more difficult to achieve had I built the hump in place.

[KevinMC]

I also added the lamp

I also added the lamp on the front of the sail. I used a small piece of balsa CA'd in place to support the bit of brass rod I used to replicate the lamp housing. This was all faired in with Icing.



I also built up the raised features on the side of the sail. I've no idea what the forward one is, but the aft (right) bit is the port nav-light modeled in the retracted position.



The Sierra hump well cured in place, I went back to my photo collection started second guessing the height I'd created as what I had looked too tall. (Doh!) I reprofiled the height of the hump but managed to stay away from the intersecting area on the top of the sail.





This also gave me the opportunity to improve the recessed detail on top of the hump which looked too simplistic the first time. I've given the sail a last shot of regular primer and peeled up all the panel tape now.









Now it's onto the fins and cooler scoopes.

[KevinMC]

I've started building the stern

I've started building the stern horizontal and ventral planes. In somewhat of a departure from my "using readily available materials" theme, (and thanks to repeated prodding in the background from a certain Sub Master) I got hold of a small brick of RenShape 540 from a local prototyping shop. For anyone that hasn't tried it, this is some really great stuff!!! Here are a couple of blocks I've cut out in preparation for plane construction.



I 3M77'd paper a template to each block. Note that each block is double the thickness of what it really needs to be- this is so I can cut the profile of both the L and R planes in a single step. Then I'll use a bandsaw to separate the L and R halves.

[KevinMC]

Oye! I'm getting behind.

I stayed

Oye! I'm getting behind.

I stayed up a while last night sanding the fins to shape. I can't speak highly enough of this RenShape. With it I've made more accurate, crisper fins in a fraction of the time it took for me to make the previous set out of balsa.

After splitting the fin "blanks" I marked the midpoint (using the previously shown pencil spaced off the table trick) and then glued paper tip and root templates to each. (Still visible on the horizontal mainplanes.) With templates in place, I went to work on the disk/belt sander to rough the fins down to shape. Final shape sanding was accomplished with 220 grit paper on a block, the results shown here


I also started cutting the rudders from the ventral fins. This was done by first marking where to cut...



Then the marked lines were scored with a sharp hobby knife.



Finally, the parts that could be accessed with a razor saw were sawed, the parts that could not were repeatedly scored with the knife until the moveable part could be snapped off. Did I mention I'm thoroughly impressed with this RenShape stuff?



There should actually be one more shot to this sequence, but I somehow forgot to take it. I took things to the next step where I also drilled the hole for the torque rod and final sanded the parts. (I'll have it up tomorrow...)