Monday, August 10, 2009

silicon casting

This weekend I made my first foray into the wonderful world of silicon molds and resin casting!!

I picked up some supplies from and have so far found the guy to be helpful.

While waiting for the supplies to be delivered (UPS ground – I expected the full 10 days, but they really only took 3 or 4!), I made a few mold boxes with Legos and based some multi-piece metal model parts in clay as a foundation; these Legos will be forevermore dedicated to molds and casting, I bought lime green and orange so I remember to NOT mix them with the others I have collected over the years and plan to hand off to my grandchildren some day

I went out Saturday and bought several different sized dixie cups for measuring and mixing and poured the first halves of 2 two-part molds Saturday afternoon. The silicon I am using sets up in just over an hour, so I was able to strip the mold box down enough to pull off the clay base layer, swab the silicon with petroleum jelly, rebuild the box and pour the remaining half around mid evening. On the weekends I tend to stay up until 1am and actually managed to do my first resin cast in the molds before going to bed.

I was casting copies of a grav-bike from the game Void, which is a pretty spiffy model in my opinion. I plan to convert it over for use as a Tau Tetra for Warhammer 40,000, but I didn’t want to mangle the original because the company (i-Kore) has shut down (I’ll try to paint it up good enough to display).

I was also trying to make a copy of mini tank treads from an old GW Imperial Guard heavy weapon platform ( forget the name). This too is a multi-piece metal figure I’d like to NOT mangle, the casts are going to become the treads of an Adeptus Mechanicus heavy weapon servitor conversion.

The grav-bike pieces came out pretty good. I discovered that I got some bubbles in the mold, but the resin piece cleaned up nicely with a new X-Acto blade. I also discovered that the silicon mold picked up brush marks from where I used a large artists brush to swab petroleum jelly around between pours. The first cast picked up all the residual clay and petroleum jelly that was left in the mold and a second cast I did on Sunday came out nearly perfect. I need to find a way to patch the bubbles in the mold; I have an idea, but I am waiting for the guy from the supplier to get back to me about it. The brush marks that are in the mold should sand off the cast no problem.

The mini treads did NOT come out well at all!!! The way I set the mold up caused air bubbles to get trapped at critical points and I lost entire sections of the cast! I tried to clean up (expand) the air channels in the mold, but the second cast came out as bad as the first! If I can fix the bubbles in the grav-bike mold the way I think I can, I’ll do similar to fill in the pour spout on the treads mold and then cut new ones. The problem is that I did this as a tall, vertical mold where the resin is supposed to flow down through one piece and fill the other and continue to the top. Sounds great on paper, but didn’t work out well in practice. If I can plug the fill spout, I’ll cut new fill spouts and air channels so that I am filling the mold from a side; otherwise I’ll have to redo the mold.

Late last night I bit the bullet and tried to pour the silicon for a big block mold around an original defense barrier made from clay sculpted over Legos. The first batch of silicon only filled the mold box about half way, so I quickly made another batch and poured it in as well. The second batch left the mold about a quarter of an inch from the top and I knew that would mean there is less than a quarter of an inch of silicon over the highest point of the sculpt so I made up a little more and poured that in as well. I used my stirring stick (a popsicle stick) to try and integrate the three layers of still semi-liquid silicon.

This pour proved that I am having trouble getting a consistent mix with my current methods… By the time I got to the bottom of the mixing cup I saw that I needed to mix the two parts more and that showed consistently across all three portions of the pour.

I stripped the mold box off this morning before heading to work and I found that there were still several pockets of liquid silicon inside the mold. Fortunately, the skin of the mold didn’t tear and gush out the gooey liquid silicon! I put the mold out on the railing of the stairs to my apartment in hopes that the 90 plus temps today will help the mold finish curing. I’m hoping to get at least one good resin cast from this mold so that it isn’t a total failure that used about 3/8 of the silicon I paid $100 for… It doesn’t help that I had to destroy the original clay sculpt to get it out of the mold (this is a failing do to inexperience on my part, not the casting/mold making process – I have seen YouTube videos of other people where this doesn’t happen).

If things turn out well, I'll be fleshing the defense barrier out into a full line of terrain to sell. Then I am going to move on to sculpting an actual trench piece based on some photos from the first World War that will mount in a gaming board rather just sit on top of it.

I might do some scenic bases to sell as well, but I'm not sure yet... There is a ton of competition in that arena and I know a guy that does that already and wouldn't want to step on his toes.

I had planned to do some 15mm buildings for Flames of War, but I haven't gotten around to building the originals yet.

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