module mycube(x, y, h){
minkowski() {
// make rounded edge
 $fn = 45;
 cylinder(h, 1);
 cube(size=[x,y,h]);
 } 
}

module mycylinder(h,r){
// 
 $fa = 1;  // maximum size of the facets
 $fs = 0.1; // maximum angle of the facets
 translate([5,26,0])
 cylinder(h, r);
 translate([5,28.5,0])
 cylinder(h, r);
 translate([5,31,0])
 cylinder(h,r);
}

difference(){    
union(){
    mycube(10,80,1.5);
    mycylinder(7,1);   
}
 translate([5,17,-1])
 cylinder(20, 1);

}