Griglia casse

Griglia utilizzata per montare delle casse da 7cm su una tavoletta di legno.
questo il codice openscad:

difference(){
translate ([0,0,-3]) cylinder (3,47,50, $fn=100);
for (a=[0:20:340])
rotate (a){
for (i=[3:5])
translate ([0 + i*6,0,-5]) cylinder (8,1.2+i/2,.9+i/8, $fn=100);
}
translate ([0,0,-3]) cylinder (4,15,1, $fn=100);
translate ([0,0,-4]) cylinder (2,40,36, $fn=100);
for (a=[0:90:360])
rotate (a) {
translate ([-42.5,0,-3.1]) cylinder (4,3.5,2, $fn=100);
}
}
difference(){
translate ([0,0,-4]) cylinder (2,5,14.5, $fn=100);
translate ([0,0,-5]) cylinder (7,10.5,12.8, $fn=100);
}