Preliminary sketch of an octahedron.

Here is a quick exercise I did to study intersections from cylinders to spheres.

The following were sketches I did a while back changing the template to Google Sketchup's crayon or charcoal, if I recall correctly. It imitates looser line in a sketch.

Wavy Cube 2

After reducing the wave amplitude.

Wavy Cube ~ Before Trimming Overlapping Intersects

Modulated Cube

Staying with five cycles of waves (across the diagonal on cube faces I lessened the amplitude of the cycles by half and got the above result.