Hello Tim,

In SpaceClaim, on the Design tab, first create a solid body in the shape you want to have split from the larger part, then use the Combine tool to subtract from the larger target body the new tool body you created. It will create a third body of the intersection of the target and tool bodies, so you will have to delete the tool body when you are done.

If you don't want to use contact to connect these two bodies, go to the Workbench tab and click the Share button to have the mesh connect them.