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Rubber Domes with Stems

So I've been playing with the new molds I had made. I had a large sheet machined with 24 dome-side molds, and 8 stem-side molds.

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The dome-side molds can be used by themselves in the method described in the OP, or can be combined with a stem-side mold to create a stemmed dart tip. The stem makes the process of centering and attaching the dome much easier, but due to the increase in the amount of silicone and the decrease in aerobic surface area, the cure time is drastically longer. If the stemmed darts are to be made in one step using normal caulking silicone, the cure time is a little bit over 2 weeks, although a 2-step process can reduce this to about 1 week.

For the 1-step process, simply overfill all of the domes, then bolt on the stem-side sheet. As you tighten the 2 sides together, the extra silicone will rise up to fill the stem-side of the mold. Then wait at least 2 weeks, and separate the 2 molds. Normally, the tips will stick to the stem-side, and should be pushed through rather than pulled out to avoid tearing at the neck of the dart tip. 

The 1-step process can also be used with the anaerobic, mixed silicone RTVs to avoid the long cure time, but my experience is that this is more trouble than it's worth. The stuff that we used is about 3 times as expensive as the caulking silicone, doesn't come in a convenient dispensing cartridge, and has a lower viscosity prior to curing which generally leads to more waste. And then, you still have to mix another batch to attach the heads. It's much faster, but much more work.

For the 2-step process, fill and wipe the dome-side mold as usual, wait for it to cure, then add more silicone and bolt on the stem side sheet. Once again, the silicone will rise up the stem as the two sheets are tightened together. This process still takes about a week, with 2 days for the domes to cure, and ~5 days for the stems to cure and fuse with the domes.

Separating the molds can be tricky, I've usually used a razor blade to pry them apart. There are a variety of simple fixes for this that I keep forgetting to implement.

Although stems made with polyurethane goo might be easier to affix to the foam, my experience indicates that they take about twice as long to cure, which is even more impractical with the dome+stem method than caulking silicone.

The molds are now for sale here

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