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.
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 10:30. Arrived at the Carmel pond at 12:10. I was pouring down rain at this time and there were no Subron 6 members to be found.It stopped raining about 10 minutes later, but there was no one to show the boat to. So here's a photo of it in the back of the van—woo hoo!
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...