Sinoid Sphere Plotter - fz(a,b) = sin( 2a )

Customized version of http://www.thingiverse.com/thing:175490

This Thing is made with the Version 1 of the sinoid sphere plotter using this functions:

function rx(a,b) = cos(a )*cos(b )*gr ;
function ry(a,b) = sin(a)*cos(b )gr;
function rz(a,b) = sin( a2 ) *gr;