We used MDF sheet 4mm. thickness to make a sphere which is self-structure by the connecting of outer rings (vertical) to inner rings (horizontal). For us. less is more. One single vertical ring can make other ones together, so we don’t need another ring.   For inner rings, MDF sheet was lasered cut into each pieces in different radius but for the outer ring, we have divided it precisely and laser cut it to connect with inner rings. To make the over structure be more rigid, we need to laser cut the joint between end point of each outer ring in the locking shape by itself   Finally, we connected all pieces together then we got the minimal clean sphere diameter 12 cm. which is  the hollow core without any supporting element.