//initial version from https://www.instructables.com/OpenSCAD-The-Instructable/

$fn=100;
cube_side=10;
rad=0.7*cube_side;
cylrad=rad/3;
cylht=2*cube_side;
difference()
{ 
   // // intersection()
    // //{
       // //    cube([cube_side,cube_side,cube_side],center=true);
       sphere(r=rad);
   // // }
  union()
    {   
        union()
        {   
            rotate([0,60,0]) 
            cylinder(r=cylrad,h=cylht,center=true);
            cylinder(r=cylrad,h=cylht,center=true);
        }
        rotate([0,120,0]) 
        cylinder(r=cylrad,h=cylht, center=true);
    }
    union()
    {   
        union()
        {   
            rotate([60,0,0]) 
            cylinder(r=cylrad,h=cylht,center=true);
            cylinder(r=cylrad,h=cylht,center=true);
        }
        rotate([120,0,0]) 
        cylinder(r=cylrad,h=cylht, center=true);
    }
      sphere(r=0.8*rad);
}