Chatting with @bradcozine about various investments to use. Feel free to chime in on what you use and preference on techniques.
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What is the mix you’re using now for PLA and what burnout process?
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It depends. Sometimes suspendaslurry for my larger casts. #1 plaster mix with pool filter sand for smaller casts. I use my fire pit to burn out. Oak charcoal. Create a red out coal base. Insert the mold then cover with oak coal. And light the oak from the top. It does just fine for the shell molds. The plaster mix molds are hot or miss.
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The suspendaslurry acts as an exoskeleton keeping things together, which is why you’re probably having greater success with those castings. Your plaster only castings may be having issues due to thermal expansion or moisture trapped in the filament causing outgassing expansion. You may want to try making sure the PLA has been dried before printing and also annealing the PLA print to ensure that any trapped moisture is removed.
It’s possible that the plaster mix that you’re using has not dried sufficiently before burnout or is not porous enough. This guide on Lost PLA mentions using the two investments from Ransom and Randolph I had mentioned in our conversation… Uultravest and Plasticast.
I have a box of Plasticast at home and some Ultravest at work for you to try on a tricky model.
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I was partly assuming my issue with the plaster was my burn out. It’s such an inconsistent heat that the plaster wasn’t burning off properly. I really don’t want to have to invest in an oven. I also preheat all my molds for an hour at 450 before pouring. Really it’s the plaster mix I seem to have the most issues with. I have found ways to make the cast come out better with what I am doing. Mostly with orientation of the models. Right now just using plaster mix for coins cast in Nordic gold.
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