Tag Archives | mold design

Unusual shapes

There was no question that I would need to cast Elsie’s tail separately. What I hoped was that once I cut it free from the sculpture, I could find some kind of angle that would simplify the shape for mold-making. As it turns out, there wasn’t a magic angle. It was a shape that didn’t work well from any angle, and I was stumped about where to draw the mold lines.

I finally decided that I’d clay up one side, pour the first side piece and figure out what to do from there. I had high hopes that the planes would suddenly make sense once one was covered, but I also knew that I had rapidly degenerating rubber components. Polyurethane prepolymer (rubber Part A) degrades after it has been exposed to air, so I needed to use what I had left quickly. Experimenting seemed like a good idea.

The process did work, though there really wasn’t a simple answer. The strands of the tail move in too many directions for anything but a fairly complex mold. Right now I think it will be a five piece mold, though the area that fits inside the bend may work better broken from the rest of that piece. That’s five, possibly six, pieces and we haven’t made it to the body yet!

Meanwhile Oliver’s two production molds are about half-dry. I am dying to test them.

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Ponies that wear hats and ponies that don’t

Around here, most ponies wear hats. That’s because ears create an undercut; the area between them is hidden. So unless the mane is thick enough to cover the space between, there is a mold piece that goes there.

When horses have turned heads, there is sometimes a second piece that fits over the head or the head and neck. Both Finn and Vixen have these. I had assumed that Elsie would need a hat and most likely a second piece since her head and neck turn quite a bit. But after looking at her a bit, I’m rethinking that part.

One of the first things I did, back when I first started learning to make molds, was draw hypothetical mold lines on many of the Hagen-Renaker minis. I figured they were good examples since they were made with the same process (earthenware slip from plaster molds) and they were mass produced and sold relatively inexpensively. If anyone knew how to make workable molds, it would have to be them!

What I noticed was that many of the horses had heads that turned just right. That is, the turn shifted the ears and even the nostrils to one side of the mold. The rough outline of their mule above shows how this works. See how both the ears are visible? Nothing is hidden, so the mold can pull freely without the ‘hat’.

What I’ve found intriguing about Elsie is that her ears are the same way. I’m not sure I can design the mold to eliminate the hat altogether, but I have been surprised by just how much of her face is on the same plane.

But before I can think much about her face, I have her tail to worry about. As the picture shows, I was was able to cut it free with a jeweler’s saw. I am finding its abstract shape an absolute bear to mark for mold lines. Unlike a four-legged animal it isn’t an obviously two-sided object. I’ve decided to have a go at claying it up with only one set of lines drawn (the one side I can see clearly), and then seeing where I am.

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