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1/96 Ohio SSBN/SSGN build underway

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Postby Wayne Frey » Sun Apr 20, 2008 1:44 pm

Any updates Pete? It is getting close :)
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Postby Pirate » Fri May 02, 2008 12:00 am

I'mmm baaaack.

I've been building. I've been building the sail. I found from my information that the sail needed to be a little larger than the one given to me by another model builder.

That sail was made in two pieces; the bottom–built open on both the top and bottom like a tube, and the top like a cap.
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THe bottom part has a mold with a protrusion coming down from the top half that goes down through the center. This part is hard to get out of the cast part.

I built the sails to my Seawolf and Virginia as one piece, but that still required the protruding part of the rubber mold to make the center hollow on the casting. Again, it is hard to get out, and makes it easy for the mold to get torn and therefore easily ruined. This is my Virginia sail and mold.
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For this Ohio model I wanted to do it a little different. One problem in shaping the sail by hand is getting the curve around both sides of the sail to be symmetrical. But if I make one half that can be used for both sides, then they are sure to be symmetrical. Then also it will only need a simple two-part mold.

I started by making one side from MDF wood.

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Then I made a two-part mold for it.

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I cast two pieces in it in a Harbor Freight pressure pot.

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I created a tab system on the back sides of each, then fit them together. With them together I could shape the curve on the bottom to fit the forward slope on the turtleback deck. Once these are detailed I will make a new mold for each side. These will reproduce much easier and quicker with less rejected pieces. This picture shows the two halves tacked together to get everything lined up and detailed.

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Next step was to make the sail planes. Since these are also symmetrical, I could make one and duplicate it for the other side. I made one, then sanded it against the side of the sail to get the curve to match up perfect. Then I applied a piece of the chart tape that I used to detail the hull around the sail where the articulation is supposed to be. I then painted it to get a recessed line at that point.

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I like using the square brass shafts for the control surfaces because the control horns will not slip and rotate around it like they can on a round rod.

I made a mold of this piece and made two castings. Then I cut them at the line with a razor saw.

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I attached the short, curved piece to the side of the sail. And then repeated this for the other side. Since both sails are identical, I'll only need one mold for both side sail planes.

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I filled and finished off the sail plane roots. Made the side marker lights and attached them, and applied the rest of the details to the sides, including the diesel exhaust ports, the radar window, the dive horn and the floating antenna on the port side.

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I made the top piece out of MDF also.

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Here are some shots of the sail master completed, although I still need to add the holes on top for all the masts—that's next. Then molds for each part.

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Pete
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Postby Rogue Sub » Fri May 02, 2008 7:12 am

oh crap pete you are almost there buddy! Just have to finish of the back end and prop and your there. Think you will have the master done for the Regatta?
Excellent jog with the sail. You got the diesel exhaust, floating wire and even the ships horn. BZ
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Postby Pirate » Fri May 02, 2008 8:48 am

Kevin,
Thanks.
Hey, I'm not understanding how the safety track is raised on the back end of the turtleback.

Does it come way off the deck to flow smoothly into the part of it on the hull, or does it curve down with the shape of the turtleback to the deck, which seems to me like that would cause a funny kink in it?

Can you draw me a side-view of where in comes off the turtleback into the deck?

Thanks.
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Postby Rogue Sub » Fri May 02, 2008 9:48 am

thereis not funky kink it is a smooth transition.
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Postby Scott T » Fri May 02, 2008 1:02 pm

You say its hard to get the plug out of the middle of
the sail. Could you put a hole down through the
plug and cover hole with tape, then use air to blow into
the hole to pop casting off the plug?

I saw something like this over on a SP hull building thread.
Seems like the air might give even force to push the finished
piece off.

Or shove a rod through the hole to push the finished piece off?

-Scott
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Postby Pirate » Fri May 02, 2008 2:00 pm

Scott,
That's a good suggestion, but the mold piece is soft RTV rubber. The friction caused from the sides being so long (deep) against rubber does not move too easily. And a rod would just poke into the rubber in that spot.

As well, the hole would have to be in the top of the sail where one is not desired.

The process you're describing works very well against hard molds though.
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Postby Scott T » Fri May 02, 2008 3:52 pm

Here is what I was thinking it might look like. The image is better at
the url listed.

http://subcommittee.com/SubComm/images/photos/00%20mold%20release.jpg

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The tube would push against the hard casting.
The air would lubricate or lift the mold, sort of
like a hover craft.
If the air bleeds out to much in one area, pinch it
closed at that spot and another leak should start.
Pinch it all the way around and it might balloon
out the rubber mold.

edit: how about shooting soapy water in to get it sliding
edit two: update drawing

-Scott
Last edited by Scott T on Mon May 05, 2008 4:25 pm, edited 1 time in total.
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Postby wlambing » Fri May 02, 2008 4:54 pm

Pete,

I couldn't tell from the pics, but I think you may have missed the taper on the upper leading edge of the sail. On T-hulls the sail angles with a slight sweep as you go upwards from the SONAR window to the top. There may also be an angle on the sides, above the running lights, resulting in the sail top being slightly thinner in cross-section than the sail base (below the running lights). A good profile and head on photo will reveal the angles for you.
Very nice work, in general! Keep it up!!!!

Take care,

Bill
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Postby Pirate » Fri May 02, 2008 9:24 pm

Scott,

I think you misunderstood the configuration. Look again at the top of the page at the photo of the Virginia sail and mold sitting together.

What you've drawn as a hard casting to push out is actually the soft RTV mold on it. So the hole would need to be through the top of the sail and push the soft rubber out from inside of it.

No bother though. I get by using it to make multiples. It's just very delicate work de-molding it.
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Postby Pirate » Fri May 02, 2008 9:30 pm

Bill,

Thanks for that info. The source I have for plans does show that taper from looking at the sail head on. But at scale it's not even a 1/16" difference from the side at the plane root to the top. I didn't think it would be too noticeable at this size. But I guess if I'm going to show close up pictures like this it better be right, or someone will notice, huh? Someone named Bill.

After looking at the plans again, I need to add more curve over the top. So I may go ahead and add this taper.

For you guys who are wanting your model sooner, it's Bill's fault. ;)

Pete
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Postby wlambing » Sat May 03, 2008 9:17 am

Pete,
I'll carry the weight on the that one, for I have broad shoulders, big feet, and practiced as a Senior Chief Petty Officer in the Finest Navy The Planet has ever known!! ;^)
Actually, the angles are very prominent in all the pictures and real life.

Take care,

Bill
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Postby Pirate » Mon May 05, 2008 11:19 am

Okay guys, I took another look at my reference and added the taper at the top of the sail. And it also tapers at the bottom of the sail. So that has been changed too. Doing this gave a more accurate curve to the top piece as well, which wasn't quite right before either. And while I was looking at the reference material again, I took some more measurements and found that the sail planes were a bit to bulky at the ends. I thought they looked kind of heavy. So that has been changed as well. Thanks Bill. Really, for your expertise.

Pictures of the new and improved sail to come tonight after I get some new sail planes out of the new mold which has been curing overnight.

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Postby Pirate » Tue May 06, 2008 12:19 am

Alrighty then. The plan shows the taper at both the top and the bottom.
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So in this picture I have the new and improved, tapered sail. There is a new, slimmed down sail plane on the right, and the old, fat, over-weight one on the left. See the difference?

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And the curve over the top of the top cap is now on the money too.
This shot shows both new sail planes sitting in place. It's kind of cock-eyed (the camera angle), and it's looking up at them just a tad, but I think you can still tell they are thinner.

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Here I've started to make a new mold for the stern plane roots. I added those little brass pins in the root of the plane (towards the bottom of the photo) so that they'll be part of any new casting. They line up with the hole markings I made on on the hull to help more quickly and easily line up the stern planes when mounting them, and help them stay on better.

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I'm going to make a urethane plastic tail piece that will have the propeller shaft hole pre-drilled to accept a bushing. This will go on after cutting the marked section off of the hull pieces and line up perfectly. The shaft, propeller, bushing and dogbone can all be mounted to the stern as one assembly then. This will eliminate having to getup into the stern from the inside, past the linkages, to try to hook things up.

After that, I think it's off to making tools for everything like the one for this stern plane root.

Kevin McLeod, I got some of that Smooth-on RTV to try. The 930-blue. This stuff has a really high shear strength. It's almost impossible to tear, and I haven't post-cured the first mold I made for the sail planes yet. After that, I can't imagine how many castings I'll be able to get out of it. Truely great stuff! Thanks for the info on that.

Pete
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Postby KevinMc » Tue May 06, 2008 7:03 am

Woo hoo- McLeod's spelled right! 8) Oh yeah, and good work too. ;)

I'm glad to hear you're having success with the SmoothOn products. How'd you get turned on to the 930 product? I used 920, which is really easy to mix 'cause it's 1:1 by volume.
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