Advance Fee Fraud (day 66)

Today I separated the mold halves for the upper leg and used epoxy putty to make hollow copies of the part. I also added a bit of missing detail to the sole of the foot.


I built the sole detail for the foot back in 2010 or so, I guess, but apparently I missed a spot, so I took a little time to correct that.

After waiting for a couple days for the mold rubber to cure fully I decided I didn’t feel like waiting any longer, so I pulled the mold halves apart. They separated very easily, except for one spot where I had tried to use mold rubber to repair an air bubble in the first half of the mold… This made the two halves of the mold bonded to gether at that spot, and I had to tear them apart at that spot to separate them. This in turn revealed another, larger bubble in the mold under the location where the first one was… This kind of thing is why I need to get set up for pressure casting again.

With the mold separated I decided to move forward and attempt a casting from it. For these cast parts I’m using a technique I haven’t used previously: instead of pouring liquid resin into the mold, I’m manually applying epoxy putty to the inner surface of the mold. I’m doing it this way to produce a hollow part without needing a technique like slush-casting. Doing things this way wouldn’t be great at capturing detail probably but since there’s not much detail on this part, it’s OK.
This process played out a little differently than I’d expected: I found it a little harder than expected to apply the epoxy putty to the inner surface of the mold, and while manipulating the putty, it would often separate from the mold walls. When I pulled the first casting I did with this method, the resulting part had a lot of gaps where different bits of epoxy putty had come together without blending properly.

After giving the first hollow-cast leg part time to cure, I removed it from the mold and did another casting. This time I tried to apply all the epoxy putty for each half of the mold as a single sheet of material, so there wouldn’t be as much need for different sections to knit together. The results still aren’t perfect but I think it’s a big improvement. (I am tempted to do a third casting so I don’t have to use the first one…)

At this point the parts are cured enough that I can remove them from the mold and not feel they’re going to warp or collapse… When they’re fully-cured, I can begin the process of differentiating them for the left and right sides of the body, and adding functional bits, like joints for connecting to the knee and hip and the connection point for the leg power cables.

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