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Unread 03-14-2013, 06:57 PM   #13
msleeper
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Whoops, forgot about my thread here! The spam filter eating my posts kind of discourages me.

So last I posted, we were about to mold and cast the rear base. That didn't go so great. My inexperience has caused me some problems that made fixing interesting.

To try and conserve some silicone while filling in the big gaps (namely, between the "drums" where there is a deep valley) I shredded up an old silicone mold and put it in one of the layers. Well, that was apparently not the smartest idea after all because the two silicones didn't stick to one another, and actually caused the silicone immediately around the shreds/chunks to not cure at all.

(I have since found out the cause for this: tin cure silicone will not stick to platinum cure silicone. This is really interesting as I've never heard this before, all I've ever read is "silicone always sticks to silicone". So take notes, true believers!)

What this caused is these hollow spots along these areas where resin got into. Not the end of the world, but definitely a problem I didn't want or plan on having. The bigger problem is that when trying to demold this part I had no choice but to cut out some of the silicone here. So, any further pulls are going to immediately have this awful cleanup needing to be done in these spots.

That wouldn't be as much of an issue if I wasn't going to need at least 1 more pull from the mold. There were some minor alignment / sagging problems, mostly due to thin sections of silicone, at the "top" of the mold where the 3" pipe section is, and on the actual drums. My second pull had less problems and I've decided to go ahead with using it.

It's not a complete disaster, but this whole fiasco is definitely the sloppiest and most expensive mistake I've made thus far on the project. I'm not super happy with the results, but I have got to continue moving forward. Unfortunately the only way to fix the problem is to remold it the master, and if I'm going to remold it then I might as well just remaster it too. Since I'm not made of money that won't happen right away, but I would like to eventually. My coworker has offered to let me use his 3D printer (which printed the heatsink) for other parts, so maybe if I can break things down small enough to fit into his machine.

What's absolute brilliant news though is that the entire rear section is only 1.5 pounds, which is about 80% lighter than the plaster. Weight was going to be a major factor here so having things be as light as I can get them is great.

So, on to the picture show. Here's a montage of building up the silicone and the mother. I can only post 6 images, so check out my Imgur album for lots more.





Here's the first casting that I've made. You can see the pockets where the silicone chunks were filled in with resin.



Here's the the "front" part where the silicone was too thin, so the whole thing sagged in on itself in the mother. The upside is that all of the hard edges are still square, so I can fill in the sagging with putty and not have it be a total bust. Still, it sucks that it could have been an easily fixed problem by buying/using more silicone.





But it's not an entire wash I guess . . .



. . . I still have a Gravity Gun now.

The next step is to clean up my (far superior) second casting, and then start assembling and painting this mother.
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