Looks like there are still a few issues with repeatability left to solve but I got pointed to new tools and processes which might help. I also had a lengthy discussion with a Rio Grande dealer about how I am doing my investing, so I think I have a good chance of increasing the number of good casts out of each batch.

Some interesting things that came up:

- When putting sprues on, both the sprues and the model have to be very clean (i.e. trim all imperfections with hot knife and exacto knife). Investment will get in those and then break off during burn-out, fall on cosmetic surfaces as dust and jagged particles and get imprinted in the casting.
- Fewer sprues is actually better, because that will create less turbulence of streams of metal mixing together and possibly destroying more investment on the inside.
- More investment & less water for heavy pieces.
- Instead of doing the complete burn out inside a kiln (which so far has cost me $300/month due to having to replace burnt out coils, not to speak of black smoke that gets everywhere), flasks can be boiled in a pressure cooker/canner, which gets most of the wax out in a very clean way. It can then be collected from the bottom of the cooker in one piece and thrown away
- Jewelers use flex-shaft tools for chasing and finishing work, which are stronger than dremels - got one to try it out
- Got sticky wax and a wax warming pot (that looks like a little food tray with sections and a built-in hot plate). Apparently sticky wax, besides helping to put the sprues on quicker, is a much stronger bond after cooling (not flexible). Got a hot knife also (waxer pen with tips and a wire going to the power supply with potentiometer).
- Got more pre-made sprue sizes
- Longer burnouts are necessary both for larger flasks and for detailed parts. The longer burnout will harden investment more and not let metal destroy small details when swirling inside.
- It's good that I've been using risers, that still helps even with vacuum casting