Example openscad

example.scad

// Ensure objects have a sufficient number of faces.
$fn = 30;

// Draw a flat panel 100mm * 100mm * 3mm and then remove 3mm holes for screws.

panel_size = 100;
screw_size = 3;
screw_distance_from_edge = 10;


difference() {
    cube([panel_size,panel_size,3]);
    translate([screw_distance_from_edge,screw_distance_from_edge,-1]) {
        cylinder(d=screw_size, h=5);
    }
    translate([screw_distance_from_edge,panel_size-screw_distance_from_edge,-1]) {
        cylinder(d=screw_size, h=5);
    }
    translate([panel_size-screw_distance_from_edge,screw_distance_from_edge,-1]) {
        cylinder(d=screw_size, h=5);
    }
    translate([panel_size-screw_distance_from_edge,panel_size-screw_distance_from_edge,-1]) {
        cylinder(d=screw_size, h=5);
    }
}