I’m going to post as much as I can about the cylinder casting process on here, Jurrian and I have exchanged a lot of emails (he either speaks excellent English or is kind enough to translate for me) and I think we have a good plan. He owns the design of the cylinder, porting, etc so I won’t share those numbers, but since I’m developing the casting process I will post what I learn.
I have decided to try the ‘swing for the fences’ approach and do a direct burn out lost-PLA. In this process the positive is 3d printed from PLA using an FDM printer, then it is cast in a block of plaster, and put in a burnout oven to melt the plastic out. Molten metal is poured into the cavity left behind and when it cools, the plaster is broken away. This is the fastest process when it works, but can be extremely frustrating when it fails since you waste a week of work, and a lot of money in plaster.
I’ve only successfully cast one part with this method, but I learned a lot after failing 8 times that will help me with this part. Its 8 less failures I will have on this one. The most important thing is to design the mold flow into the 3d printed part. The plaster is very brittle during the burnout process and breaks easily if there are small unsupported pieces so I’ve asked Jurrian to make some design changes to the fins and some other parts to ensure the plaster is well supported and structurally sound.