Why not use an investment casting method for this?From what I have been reading, people heat the plastic up to get it soft enough to withdrawl from the sand, but avoid overheating the sand.
Apparently bound sand can take a lot of heating.
I think I was reading about sodium-silicate molds getting heated to allow removal of the 3D print.
I have flamed resin-binder molds with a gentle propane flame, and also burned off the moldcoat, without problems, so they are pretty heat resistant.
Hopefully I will not have to get the 3D print fully molten to remove it from the sand.
I am thinking about using a 2-part print, with a removeable round core that takes up perhaps 80% of the print, and then separately print the teeth with a little backing. Then I can remove the center part of the gear, and then heat and remove the teeth.
A bound sand mold I think will be as accurate as a ceramic shell, or almost as accurate depending on how well the teeth spaces ram.
This may be a case where excess binder is used, which makes for a very hard mold or core, but that may be desirable, unless the mold gets too hard and prevents expansion of the molten metal.