1/96 Ohio SSBN/SSGN build underway

[Rogue Sub]

Wow Pete I couldnt even

Wow Pete I couldnt even find the discrpency in the sail until I enlarged your pic and looked at mine.

Some one have a photographic memory over there in New England? Ill see you boys soon enough!

[pirate]

Kevin,

They have a whole list

Kevin,

They have a whole list from 910 to 950. The last two digits is the shore hardness. So 930 is right in the middle of that as far as how stiff or flexible the mold will be. THat determines how well it will hold its shape without a mother-mold, or even in a mother-mold. With my Seawolf mold I have a hard time keeping the mold up on the sides of the mother-mold, even with keys, because it isn't stiff enough. With this one going to be even longer I don't want that problem. But yes, it is kind of hard to mix—very thick—but surprisingly not too viscous.

Also, the 930 has a higher tear strength, and I have a gram scale for mixing, which isn't so bad. It mixes 100:10. Anyone know why they don't just say 10:1? Isn't it the same thing?

Pete

[davietait]

Daniel in Gibraltar has taken

Daniel in Gibraltar has taken a few photos of the USS Florida SSGN conversion Pete

http://www.fotosdebarcos.com/viewtopic.php?t=15150

Plenty of close up details for you to save to your PC for reference

Davie

[pirate]

Ok, I'm back.

I've been working

Ok, I'm back.

I've been working to make molds, in particular, one for the turtle back. But I was also able to finish the one for the stern planes. I was using the Smooth-Sil 930 (blue). I'm not very happy with it. It holds a lot of bubbles and doesn't de-air on its own well at all. And when put in a pressure pot, if there are any bubbles left on the surface of the part, they don't crush all the way. They just spread out and leave a large dimple in the mold. It's taken two tries to get this one done.

I used straws attached to the part to make the pour and air release vents.

I made a hardback from epoxy resin and glass. Once this set up I drilled three registration holes to put screws through to make sure the two halves always line up properly very time.

Next, on to the turtleback mold.


First, I got a melamine board large enough to overlap the soft mold and the hardback. I used sulfer-free clay laid down at the perimeter of the deck, then pushed it down into it to hold it to the board, and begin create a clay wall continuation so the RTV wouldn't run under the part.


I finished filling in all around the deck with clay. Once this was done I scraped away the excess clay to make it as if the deck went all the way down to the melamine board.




Here you can see the clay shaped down to the board. The next photo shows how I made a retaining wall to hold in the RTV. I also used the clay to build keys to lock the other half of the mold to.

This picture shows the first layer of RTV poured over the surface very thin to capture the details. I used a brush and made sure the RTV was rubbed into all the fine details so they'd be picked up in the rubber.

You can also see that this RTV is clear colored. I switched to the Smooth-sil 920 like what Kevin McLeod used. His was pink, but now it's clear. It flows much better and degasses on it's own better too. It also has a 4 hour demold time, whereas the 930 was 16 hours. Way too long to make much progress. That's part of what has taken so long to get this post up—no progress waiting for RTV to cure, and waiting to get the new 920.

I forgot that Kevin thinned his out for the first coat somehow. How did you do that Kevin?

I thought you wrote that you used alcohol. But I tried 91% isopropyl alcohol at 5% of the total volume on a sample batch after this and it made it very thick, not thin. Like a thixotropic mix. If you read this Kevin, tell me what exactly you used.


Second layer.


Third and fourth layer put on with a tongue depressor after thickening the mix to a non-running viscosity. Smooth-on provides a additive for this.






Here you can see little nubs I made for keys. I used little pieces of cut drinking straws as small molds for the keys.


This photo shows the epoxy gel coat layer of the hardback.


This shows the first layer of glass applied.
Next, I removed to clay barrier and slid the whole thing sideways across the melamine to break it loose from the board. I then turned it over to begin the other side of the mold.
I built a new retaining wall of clay, used a separation agent, and poored more RTV.
Here you can see spray paint cans used to take up space so I didn't need to fill the whole void with expensive RTV. I also used Legos placed in the RTV upside down to create female keys in the rubber. I learned this idea of using Legos from Tim Smalley. Fabulously simple, but brilliant idea.




Here it is cured with the cans and Legos removed.

At this point it was 2 in the morning on Friday before the Subron 6 Fun Run in Carmel. I wanted to get the entire mold done so I could demold the master to take down and show the guys. But it still needed the hardback for this half of the mold.

I got up a 6 a.m. and started laying up fiberglass for the hardback. I used polyester resin out in the garage (because of the smell) this time so it would be cured by the time I got down to Carmel, a two-hour drive. Then I planned on demolding it there to show the guys how the mold went together and the model in person.

Well, I got the fiberglass backing all laid up and was able to leave by 10][/url]
Oh, well. You guys missed it.
Here I am at the pond.


And one more, a great shot of all the boats running.


I'll demold the turtleback tomorrow at home.

What's left is to make the molds for the main hull top and bottom. I'm also going to make a small piece to replace the very end of the stern which will contain the shaft bearings. THis will allow the builder to connect the shaft, propeller and dog bone holder outside of the hull, then attach it to the hull. The hope is that this will eliminate having to get into the tiny, closed confines of the stern from inside the hull to hook this stuff up.

I'll also be building the vaunted Ohio-class scimitar prop, minus the top-secret stuff, because it's top-secret. And I don't know it either.

Until next time...

[Rogue Sub]

That sucks that you got

That sucks that you got stood up Pete. Did you at least sail your boat around the pond. I really love that place.

Looks like yopu are becoming a master at mold making Pete makes me jealous. This boat is going to be awsome.

Kevin

[KevinMC]

Hi Pete,

A small correction on

Hi Pete,

A small correction on the products I used for the OSCAR II molds- I poured initial coats on the hull using SmoothSil 920, no thinning required. (As you found, it degasses all on it's own.) I then backed it up with a several more coats of Rebound 25, which is orange in colour. (Pink RTV?!?! Really! ) The first few coats of Rebound were poured straight, later ones were thickened with Thivex turning the RVT into the consistency of peanut butter.

I also used the SmoothSil 920 for making all my appendage molds, but I had to use the pressure pot to get good results. I've posted this pic several times now, but it's highly applicable to the subject so I hope you'll forgive me for posting it again. Can you tell which half wasn't cured in the pressure pot?


Your glass hardbacks look great, and I'm sure significantly lighter than the plaster ones I made. I'll definitely be making glass ones next time round...

[scott t]

Great work on the molds.

-Scott

Great work on the molds.

-Scott

[pirate]

Well not so fast there

Well not so fast there on the mold making compliments.

I removed the underside part of the turtleback mold and find that it most likely won't have enough rigidity to make a uniform edge to the deck. The reason is because I made a soft mold piece for it as well.

Before I get the part out of the top mold I need to make a new hard mold only for the inside half.

I used the polyester resin on the previous one only to get it done in one day to be able to take it down to Carmel and show the boys. But as polyester will do, it distorted quite a bit too. So this new hardback only side of the mold I will do out of epoxy resin as was used for the top half hardback. Slower cure equals less distortion and shrinking.

So hopefully by the end of the week I'll get this done and be able to start on preparation to make molds for the main hull halves.

Pete

[pirate]

Here is the first attempt

Here is the first attempt at a second-side mold.



It won't work as planned because the rubber part will be too flimsy to force the shape of the part. And also, it's too thin to hold tyhe same shape and position on the hard back every time.

This is the other side. I glassed on some cardboard feet so it will sit level and solid while glassing the part.



So here's what I accomplished this weekend.

This is the gel coat of epoxy to redo the second part of the mold to replace the rejected one shown above. The yellow-ish areas are back-filling the keys in the RTV underneath with regular resin so the glass will lay nicely over top.



Then I glassed over the gel coat. I also added some cardboard supports that I glassed over for better rigidity across the piece to help keep it true.





I realized there was one area that if I pulled this half of the mold straight up it would catch on an undercut. So I made an area over this part to make another part of the mold that could lift out without catching on the part.



Turns out that I didn't put enough mold release in this area and this section didn't come out separately. But I realized when I parted the pieces that if I turn it out at a certain angle each time it shouldn't catch the undercut.

So I drilled holes all the way around and bolted it back together, with the part still inside, and put it up in my garage attic to finish curing fully. It gets plenty hot up there to get it all cured well. The bolts will keep the two parts securely together and registered, and then force the back down into the epoxy when casting to force a consistent shape each time.

Next was on to making the parting board for the main hull mold process. I purchased a 8' x 11" piece of melamine board to do this on. The melamine is great because nothing sticks to it. All the mold pieces come off of it real clean.

Then I marked it with the outline of the hull, and cut in 1/8" inside it so the model would rest below with the midline just above the parting board.



Once I cut out the center I made a box to attach this melamine piece to.





Then I put a few layers of duct tape along the edge to soften it so it is less likely to cut into the master sitting in it.

I put a bead of clay all the way around the edge of the opening and rested the master in it.



Next came making a clay dam to stop the RTV from running all over and to create a flat edge to the RTV mold for the hardback to register to.



Then I brushed on the first layer of RTV to make sure it filled all the details.





Once this cures, I'll add two or three more coats until it's built up to about 1/2" all the way around. And then I'll make another hardback for it.

[bigdave]

Just a note on the

Just a note on the Rebound-25. I used it directly on the hull plug to make my molds. It captures detail very well and can be brushed on to a vertical surface. Plus the act of brushing the rubber on eliminates bubbles. I brush on more layers to the desired thickness and then back it up with Smooth-on Plasti-Paste. The plasti-paste is the best I have found for making the mother mold. Excelling job so far!! BD.

[pirate]

Thanks Dave. I think I'll

Thanks Dave. I think I'll stick to the epoxy glass for the mothermold on this one. It's so long I think it will need that reinforcement to keep from distorting.

[bigdave]

You are probably correct. I

You are probably correct. I am still new to this.
That is what Plasit-Paste is though. Chopped fiberglass suspended in a plastic resin. You apply it to the rubber clove mold like frosting a cake with a plastic squeegee. Most of my molds have been MUCH smaller than yours though. BD.

[pirate]

Here's another consideration Dave, what

Here's another consideration Dave, what size container does that plasti-paste stuff come in, and how much does it cost?

Pete

[bigdave]

Price is always a major

Price is always a major consideration.
I got what they call the gallon kit which is actually 1.5 gallons in amount. It is $55. I did not think it was bad. Sure is easier. You have to work quick though as it sets up in 8 minutes. Doing it in sections in small amounts is better. BD.

[pirate]

Thanks Dave. That's about 1/4

Thanks Dave. That's about 1/4 of what I pay for epoxy gelcoat, resin and glass. I'm going to give it a try.

Darn government cut and shipping makes it 150% higher in cost though. I've about had enough of this tax stuff.

Pete