Step 3: Dismantle the proto-heart part 1
Undo the clamp.
Put the mini-tower on one of it's growth rings sides.
Mark the midpoints of the cubes.
Link the midpoints with a line. Exactly under this line lies your axis.
Draw two other lines on a parallel distance of the middle-line.
Cut the tower on the two parallel lines.
If the blade of the circular saw doesn't go deep enough - like mine's ' - finish the job with a regular saw. Or use a band saw.
Sand the two sawed surfaces with a sander.
Pay attention to have a board with equal thickness everywhere (mine's was one inch).