intersection()
{
difference()
    {
    cube(30, center = true);
        union()
        {
        sphere(r = 35/2, $fn = 200);
        cylinder(h = 100, r = 12, center = true , $fn = 200);
        rotate([90,0,0])cylinder(h = 100, r = 12, center = true , $fn = 200);
        rotate([0,90,0])cylinder(h = 100, r = 12, center = true , $fn = 200);
        }
    }
    sphere(r = 42/2, $fn = 200);
}