Questions regarding flask and vacuum setup for first casting

Hello, novice here preparing for my first casting (14k gold engagement ring) and have a couple of questions.

  1. I have just enough casting grain for the ring and not much extra at all. How should I set it in the plaster and with the sprue? Do I just make a very short sprue and put the ring near the top of the flask?

  2. My vacuum chamber is a sort where you set the entire flask inside of the chamber, put a lid on top, and turn on the vacuum. I don’t think this should be an issue for when I’m initially removing excess air when mixing the plaster. However, in my research I’ve seen people use vacuum chambers where the cover has a hole to place the flask in so that the top of the flask (where the molten metal is pulled in) is sitting on “top” of the vacuum, outside of the chamber. This makes sense as I can see how the vacuum pressure would pull the molten metal “down” into the cavity. If I place the entire flask in the chamber and put a lit over it, will my molten metal still be “pulled” into the empty space of the cavity? On the one hand I can see this still working fine as the vacuum will still pull air from within the casting and create a vacuum that pulls in the metal. However, I could also see it not pulling down correctly without the atmospheric pressure on top. Is this something I need to worry about, or should my vacuum setup be just fine as is?

Thank you for reading and please feel free to share any other advice you think would be helpful for my first casting.

Vacuum casting is complicated in that there is a lot to coordinate at the same time. I would never advise someone to do a gold engagement ring for their first casting. To be honest, that’s kind of crazy. I highly recommend that you do at least 5 castings in sterling silver before you graduate to gold. Chances are really good that you’ll mess up your first vacuum castings and then get better as you figure it out.

This is one of those things that is very hard to give advice just with written words. By any chance do you have anyone with experience near by to help mentor you in-person with your initial castings? That would be the best.

Part of the challenge with casting is that there are lots of opposing theories and they’re all potentially correct.

For instance. I think you’re talking about a perforated flask vs a solid flask. I prefer perforated flasks for vacuum casting that fit inside the casting machine, but others prefer solid flasks that sit on a table. Neither way is better for all. It’s what works best for the individual. That’s where hands on experience comes in to play.

As far as spruing goes, most people are taught to sprue the object at the thickest part. I do that, but I also don’t do that if putting the sprue in the thickest part of the object will mess it up the design.

Can you post some images of your wax models and your casting machine? That might helps us guide you better.



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I do not cast…but i recall conversations here where posters say having enough button metal to draw from is important…perhaps you can clarify how much the ring should weigh and how much total metal you have…


Did you factor in an extra 1/2 oz of metal for the sprue and the button? And do what Jeff recommended. Run experiments first with silver.
Also you will need at least 30 lbs pressure for casting. And we use solid flasks. It’s very important that the rim at the top of the flask is smooth and clean where it contacts the surface of the casting table and that the investment is not higher than the flask edge.