If you have the Power Boolean for Rhino product,
it is possible to switch
from doing NURBS Booleans to MESH Booleans. If you select meshes
or a combination of NURBS (PolySurfaces & Surfaces) as operators the
PowerBoolTree command will automatically utilize MESH Booleans. If
you select only NURBS, PowerBoolTree can convert them to meshes and
use the Mesh Boolean if you select the "MESH Booleans with MESH Result"
Boolean Engine option. The NURBS objects will be automatically meshed
prior to Boolean using the criteria specified in the "Tessellation Settings".
Note that Filleting only works with NURBS Booleans so filleting options will
be ignored by the MESH Booleans.
Note that the resulting MESH object will be a
closed "STL compliant" mesh
if the original objects are closed Rhino Meshes, PolySurfaces, or Surfaces.

Original Object produced by NURBS Booleans with
NURBS Result

Select the "Meshing" button to set the Mesh Boolean
Algorithm.

Select the Boolean Engine option to do Mesh
Booleans.

This is the resulting MESH object produced by the
Mesh Boolean.

Here we set the Maximum Edge Length to 3.0 to
produce this mesh which has more
polygons but better quality polygons.

In the case where all objects are meshes, the Mesh
Boolean will be used automatically.

This is the result of subtracing the Cylinder and
Sphere meshes from the Box mesh. Note
that you can still move the original meshes and change the Boolean operation
type just like
you can do with NURBS Booleans.

The "Clean-up Coplanar Edges" option can be used to
simplify the resulting mesh without
saccrificing the visual quality or accuracy of the result.

Note that you can still move the original meshes and
change the Boolean operation type
just like shown previously with NURBS Booleans.