Creating a void in rhino

I am trying to creat a void from outer shell
I tried nonmanifoldmerg and used creatregions to take out inner parts
This is what I usually do but When i tried with this model it goes back to original shape
how should i do it?

new model.3dm (14.5 MB)

Hello - If the parts are disjoint, then NonmanifoldMerge is your only option if you want a brep - but the normals of the inner portion will not point inward. If a mesh is OK, then Mesh the objects, Flip the normals on the inner mesh and Join to make a disjoint mesh.