Tuesday, October 20, 2009

Pouring Up Some More Test Belts

I have a few things running simultaneously right now, but I'll try to give the full update. First up is the progress on the two part mold of the back plate of the chest emblem. I poured another layer tonight, which basically makes this thing done. Just need to let it fully cure, then I should be able to start running parts out of it.

The rest of this post focuses on what I am doing with the belt mold. Overall, I am very happy with the mold. it's nice and clean. However, there are some challenges that come with it, and I'm trying to debug my pouring method so that I can predictably and repeatably get pristine pulls out of it.

I did a test yesterday that was focused on figuring out if one of the urethanes I have selected would be opaque enough for my likings. I did a couple tests with a couple different types of urethanes, along with a few different pigments. Just for testing.

You can see from that pic that there are a few different colors going on in there. Here is a closeup of the buckle:

Overall, it came out pretty clean, but I did learn some valuable lessons from this pull. First up, I'm not completely satisfied with the pigmentation on any of the urethanes I tried. The belt is just not opaque enough. Even worse, the shore strength is not right. I need to bump it up. These belts were poured at 60, which is just too soft and squishy. I need to drive it up to 80. So that was a good lesson.

So that's what I learned from this multi color belt. Not opaque enough, not rigid enough.

For the next test, I switched to a shore 75 urethane, one that I have used sucessfully in the past. I also stuck with a pigment that I knew would give me the opacity I wanted, but the cost is that it's a VERY bold yellow. Also, because the tint is not part of the "So-Strong" line that I am using elsewhere, it is a bit harder to control the way the tint behaves. If I want to soften it up a bit, by adding black, for example, it tends to turn green. Go figure.

But this test was all about pouring techniques. The goal was to try one technique and see how it pans out. The basic deal is that I poured the urethane into ONE corner of the mold, and let it seep out over the entire mold. I then laid in the straps. Here's the results:

Another problem I have noticed is that the straps tend to sink down to the bottom of the mold while the urethane is curing, and the end result is that you can see the ends of the straps through the belt. Not cool.

So I'm going to change the way I do the straps. From now on, I will do one pour to fill up the mold, and then add the straps in on a second pour. I will mix up some urethane, dip the tip of the strap into it, and then just set it down on top of the cured urethane. This will be cool, as it will also allow me to add some reinforcement to the thinner parts of the belt, like where the belt loops go.

Here is the bright yellow belt all trimmed up. If I leave it out in the sun for a few hours, it will REALLY knock down the boldness of the yellow.

Here's the last pour I did for the night. Two things I did differently this time. I left out the straps, and I used a spray in mold release. Still did the pour from one corner technique. I'm curious to see how the mold release effects it, if at all.

I forgot to outline what the real goal here is. I want a bubble free casting. Every csting I have done so far has one or two bubbles in it. Not cool. To the casual observer, I'm sure they would be invisible. But I want it to be perfect.

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