I still have a couple small voids I want to fill, but here’s the main tank. I think at this point I have filled, sanded & painted at least 5 times. I was hoping the wrappers’ slightly different thicknesses would give enough of an impression of weld lines that I wouldn’t have to do anything else to it, but all the sanding has pretty much negated that. One more layer of paint, and I’m afraid they’ll disappear all together. I will probably use some Archer .030" weld bead decals to compensate.
My end castings ended up being about .040" bigger than the body, so I re-molded & the shrinkage from that process took up most of the difference. The 2nd generation of castings was only a hair larger than the tank body, but I still had to do another round of Bondo & spot putty to even out the seam. Here it is after a fresh coat of paint. I still have a couple spots to fill & sand, but I’m almost there.
Since the body has a slight V shape, I had to do something to account for that in the connection between the body and the bolsters. I made a temporary jig to align the bolsters.
(http://burlrice.com/_LS_CornSyrup/bolster_jig1.jpg)
They’re hard to see, but on top of the bolsters are two wedge shaped castings. The patterns for these were 3d printed, using the body angle to derive the angle of the wedge. They are tacked to the bolsters with two tiny drops of CA. A larger quantity of CA is put on top of the wedges, then the body is aligned on top of the whole thing.
(http://burlrice.com/_LS_CornSyrup/bolster_jig2.jpg)
After the CA has set up, the wedges are popped off the bolsters with a flat tipped X-acto blade:
(http://burlrice.com/_LS_CornSyrup/bolster_jig3.jpg)
Then they’re beefed up with some .040" styrene. This should make it easy to keep the production castings in alignment when assembling the finished model.
(http://burlrice.com/_LS_CornSyrup/bolster_jig4.jpg)
And here’s a dry fit:
Very nice quality build. Innovative from beginning to the end
Yes, It’s great to see this level and attention to detail. I’m watching with great interest. Thank you for sharing again!
Thanks guys. It’s been an enjoyable build so far. I think there are a few things I’d do different if I did it again - but then, there always is.
Starting on the final coat of paint today. Decals (weld beads) have been applied, and all mounting holes have been drilled. I’ll have to let this dry for a couple days before I paint the top. I’d hate to get smudges on it from sitting in the cradles.
Burl,
I thought of this build the other day when BNSF had a string of these 1.5 miles long by my odometer.
I’m a little behind where I wanted to be. I had to reposition a few weld lines (I just wasn’t happy with them). Then the ice storm hit, and I couldn’t paint. Then I had to take the space heater out of my shop because a power surge fried the fan motor in our HVAC unit. Its taken about a week and a half to get back to normal around here.
How are you making the weld lines BTW?
didn’t know there was such a thing. cool.
(http://burlrice.com/_LS_CornSyrup/moldbox3.jpg)
Pulled the mold out of the mold box today.
The aluminum foil worked fairly well as a release. I still had to take a couple sides off to get the whole thing to release. One thing I learned from my previous project: the mold box needs to be able to be disassembled from the outside.
I wish I had put some stock in on the ends for spacers. As it is with the mold length equal to the inside width of the box, it is difficult to get in and out. This got fixed by cutting about 1/8" off one end of the mold.
I’ve never seen plastic casted like this before. I used to cast HD high temp ceramic sleeves from slurry at work and never thought to apply any of the techniques to model building! This is interesting stuff!
Burl
How did it come out??
Were you happy with it?
While trying to figure out how to make up for the shrinkage of the mold material, and how to get the mold out of the machine, I had the idea to use plastic sheeting. By wrapping the mold before I close up the box, it makes up for the shrinkage incurred when the RTV cured. The packaging doesn’t say what its made of, but the sheeting acts like polypropylene in that resin doesn’t stick to it. It also gives me something to hold onto when I’m taking it back out:
(http://burlrice.com/_LS_CornSyrup/moldbox4.jpg)
The first casting had too much resin heaped up on one side, and I pulled it out too early anyway. Strangely, I feel better about losing the first one. The last large mold I did poured perfectly the first time, and it took me months to figure out how to get another good one out of it.
(http://burlrice.com/_LS_CornSyrup/casting1.jpg)
My theory for the first failure is that the resin was too thin, allowing the majority of it to congregate in the bottom, instead of sticking to the walls. It accumulates heat too quickly this way, and once it begins to kick (accelerated by the heat), it stops flowing all together.
To compensate, I added micro balloons to increase the viscosity. It seemed to work. In the second casting, you can see where it has kicked. Each dark wave is one pour. This was four pours, three ounces each, giving a total of twelve ounces of resin. This photo is a 15 second exposure in a dark room, with a flashlight held to one end of the casting:
(http://burlrice.com/_LS_CornSyrup/casting2.jpg)
In the next casting, I will try increasing the viscosity with more micro balloons. I will also insert a straw in the pour hole to help the resin flow in faster. That should give me a little more working time.
Interesting Burl, Thanks for keeping us informed.
So it looks like the tank will be made up of solid resin, any idea of the weight ?
I’m not sure what I said to make you think it’s solid?
I would suspect it will weigh 12 oz, since I put 12 oz of resin in it.
What’s a micro balloon? And how does it help the resin?
Micro balloons are small hollow glass spheres. See:
http://alumilite.net/ProdDetail.cfm?Category=Dyes%20-%20Fillers&Name=Microballoons
http://www.smooth-on.com/Urethane-Plastic-a/c5_1119_1214/index.html?catdepth=1
I’m using them to make the resin thicker, so it will cling to the walls of the mold better as it rotates.