I’m designing a mold to create a plaster model and I want the model to be seamless. This is mostly a problem when it comes to the built in furniture. I’d like the mold to include the furniture since it’s a part of the building. See the pictures. I’m thinking that the inside where the furniture is could be made up of multiple pieces that fit together and hold the plaster in place while it hardens. Then the pieces would need to pull apart easily without damaging the model. I’m also thinking that the outside pieces of the mold could be made up of different sized pieces and fit together to form the entire mold. Plus the molds on the outside would be able to come off easily by sliding it out between the hexagons rails. For more context, in Rhino my model is exactly to real life scale: one foot in rhino = one foot in real life. However, my final model will be 1 foot = 1/2 inch. My printer is 9.5x9.5x9.5in. So each section of the molds needs to be within that size. Let me know of any tips or ideas. I attached photos and a copy of what I am working on in the pictures.
SPR2025PlasterMoldHelpForum.3dm (9.2 MB)
Hi @Reuland_Toby_J
I must admit it’s been many years since l did my last plaster cast, but a few thoughts:
a) Being unsupported on this corner, the roof will almost surely break unless you add reinforcements/rebars inside the plaster.
b) While it IS indeed possible to 3D print a mold that will assemble/disassemble, the practical application in this case will be very, very difficult. There’s a large number of undercuts and volumes larger than their exit, so the mold would have to be cut into several pieces and include several cores to hold the inner parts in place as the plaster is poured.
c) I would imagine that a mold from 3D printed parts will end up being not entirely leakproof and getting liquid plaster into those cores and gaps will make disassembly difficult.
d) Draft angles 
Normally you would want draft angles of at least 2°. It’s possible to go for less, but in this case, where the depth of the mold (as seen from the pouring surface) is fairly large, it will be hard to get the cores out without breaking the plaster, no matter how much release agent you spray on - especially considering the fairly rough surface of a 3D print.
e) A different approach would be to create the mold shapes from yellow foam (manually or cnc), glue them together and then disassemble the mold. The advantage of yellow foam is that you can easily cut/scrape it out afterwards. Take a look at the art of Boris Ipsum who uses this technique extensively.
My 2 cents 
-Jakob
To add to what Jakob mentioned, you need to consider venting out any air bubbles in the plaster or that will compromise the result.
Its unclear which side is up with this form, but it appears there will be issues regardless of the orientation.