For best accuracy and finish, shell molding, die casting and investment casting among others come to mind. All are capable of producing very accurate and near finished castings. Most require only light finishing and polishing for use. Exceptions of course would be surfaces requiring a machined fit such as mating surfaces, bearing housings etc., though items in this category are generally larger and not suitable for these processes, Shell molding and casting, covered in this article, will produce accurate and consistent castings, turbine blades have been produced with this method, an item normally produced by the investment process.
Shell molding and casting requires more equipment, a larger investment in materials and skill levels than green sand methods but if you require accurate small castings, once you are set up and comfortable with the process production can go quick.The most expensive part of the equipment would be the curing and heating oven, an inexpensive alternative is a toaster oven which can run at temps of 500-600*F, right were you want to be for non-ferrous work. For large work you can use the kitchen oven ( your partner might have you in the dog house for that one though, lol). Next would be the patterns, if you can make match plates you should be able to make these. Resin coated sand and silicone release agent are available at foundry supply sources.
So if you are interested here are two articles from "The Giant Book Of Metalworking Projects" on the shell molding and casting process.
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