Help making a negative mold for Cranioplasty

Hello, this is my first post here. Im a neurosurgeon from Brazil working in the public healthcare system and Im trying to give some of my patients a free 3d modelled skull.
I never worked before with 3d modelling but Ive learned quite a lot trying to make two pieces and it worked for those patients. I have used mostly meshmixer to make the "positive" mold by boolean operation and the "negative" by extruding the inner and the outter face. Like I said it worked but wasnt perfect, there are some “holes” at the edges and I couldnt solve it, so Im trying to do it using Blender now.

So what do I need is a method of making a negative 2-part mold from a concave irregular object.
The best solution I think would be is finding the largest diameter and split both faces (in and out) at this diameter.!

Or instead of creating a negative, you just split the positive model (scan) into upper and lower part (since planes have no thickness/volume) then simply use those as negative surface parts. Volume stays “perfect” aka intact, as it’s not processed, thus not modified in any way.

I have to be able to remove the acrylic after curing inside the mold that’s why I’m looking to split it at the maximum diameter. There’s any automatized macro to find it ? And I need some volume at the edges to be able to print it.

The parting line is not likely to conform to a plane.

Its possible to use Blender’s built in 3D print overhang analysis tool as a crude draft analysis, but it won’t actually split the model. In the Blender manual this image shows approx where the parting line would be.
By creating a curve that approximately matches where the dark blue changes to grey, one could split the model on the curve.

Maybe someone has made an add-on that does draft analysis and splits the model?

would it be possible to upload some sample file so we can experiment - work
and better understand the problem

might help to find a way to do it !

happy bl

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If you have the skull mesh to work with and had to do it on your own, I would suggest taking some inspiration from this https://zachariasreinhardt.com/how-to-set-up-retopology-in-blender-tutorial/

I know this is an old topic but I’ve found it quite hard to find (not expensive) ways to define non-planar parting lines on a complex surface. So I was impressed when I came across this tutorial where the whole thing is done in meshmixer.
take a look