Use a spherical modifier mesh. Create a sphere that fills the ball in your CAD file and export the STL for the sphere separately from the main part stl file. In slic3r, drop the main part on the plater, then bring in the sphere stl as a modifier mesh and set its infill to 0%.
There's a tutorial on modifier meshes here: [
slic3r.org]
If you try to print a sphere that doesn't use infill, the top of the sphere will come out very bad because it is a very steep overhang that normally would require support. It might be better to print your object as two parts, with the halves of the sphere both facing upward, then glue it together after printing.
Edited 1 time(s). Last edit at 08/20/2018 12:02PM by the_digital_dentist.
Ultra MegaMax Dominator 3D printer: [
drmrehorst.blogspot.com]