Centrifuge having a rotor with convex surface matching concave surface of nut for securing rotor on drive shaft

A centrifuge comprising:

• a motor secured to an equipment frame by elastic members, said motor having a drive shaft, an upper part of said drive shaft having a convex surface;
• a rotor having a bearing hole receiving said drive shaft, said bearing hole including a concave surface matching said convex surface of said upper part of said drive shaft;
• said rotor freely attaching and detaching from said drive shaft in a direction of turning so that said rotor engages said drive shaft with said concave surface of said bearing hole of said rotor resting on said convex surface of said upper part or said drive shaft;
• said rotor including a center, arms extending radially outward from said center, buckets attached to said arms by shafts so that the buckets can swing freely, wherein an axis of said shafts is positioned in a plane containing a center of curvature of said convex surface of said drive shaft, whereby a center of swing of said rotor is positioned within said plane containing a center of swing of said arms, said drive shaft having a top with threads, said rotor is secured to said drive shaft by a nut threaded on said threads of said drive shaft, said nut having a bottom with a concave surface, said rotor having a convex surface matching said concave surface of said nut, and said nut is tightened on said drive shaft until said concave surface of said nut rests on said convex surface of said rotor.