// Vierkante opening 13.8x19.3
difference() {
 union() {
  cube([9,10,2.2]);
  translate([9,5-20/2,0])cube([15,20,3]);
 }
 translate([9+15/2,5,-1]) cylinder(d=10,h=20,$fn=80);
}

difference() {
 translate([9+15/2,5,3]) cylinder(d=14,h=10,$fn=80);
 translate([9+15/2,5,2]) cylinder(d1=10,d2=11,h=20,$fn=80);
}
//translate([-15,-15,-1])