3d Printer roller cart

module carrito()

{
$fn = 90;
rotate(270, [0, 1, 0])
translate ([12.5,0,0])

difference (){

//main cube;
translate ([-12.5,-55,-2])
cube ([12.5,110,52]);

//hueco pa caja de bolas IZQUIERDA;
translate ([-13,-40,35])
rotate(90, [0, 1, 0])
cylinder (h=7,r=11);
translate ([-13,-40,35])
rotate(90, [0, 1, 0])
cylinder (h=20,r=9.5);

//hueco pa caja de bolas DERECHA;
translate ([-13,40,35])
rotate(90, [0, 1, 0])
cylinder (h=7,r=11);
translate ([-13,40,35])
ro