l=90;
l_bar=12.5;
w=70;
h=3;
mt=h;
$fn=100;
hole_l=76.6;
hole_w=61.72;
hole_dia=4;
arc_offset=-8;


module square(){
    difference(){
        cube([l,w,mt],center=true);
        for (x = [-hole_l/2,+hole_l/2], y = [-hole_w/2,+hole_w/2]) translate([x,y,0]){ 
            cylinder(r=hole_dia/2,h=h+0.2,center=true);
            translate([0,0,h-h/2])cylinder(r=hole_dia,h=h+0.2,center=true);
        }
        cube([l*0.85,w*0.75,mt+0.2],center=true);
        translate([l_bar,0,0])#cube([l,w+0.1,mt+0.2],center=true); //easier mounting bar
    }
}

module bracket(){
    difference(){
        rotate([90,0,0])cube([hole_l+mt*2,mt,hole_dia*2],center=true);
        for (x = [-hole_l/2,+hole_l/2]) translate([x,0,0]){ 
                cylinder(r=hole_dia/2,h=h+0.2,center=true);
              //  translate([0,0,h-h/2])cylinder(r=hole_dia,h=h+0.2,center=true);
        }
    }
    difference(){
        rotate([90,0,0])translate([0,arc_offset,0])cylinder(h=hole_dia*2,r=hole_l/2-mt,center=true);
        rotate([90,0,0])translate([0,arc_offset,0])cylinder(h=hole_dia*2+0.1,r=hole_l/2-mt*1.5,center=true);
        translate([0,0,-l/4-mt/2])cube([l,hole_dia*2+0.1,l/2],center=true);
    }
}

translate([100,0,0])square();
//translate([0,mt/2,0])rotate([-90,0,0])bracket();