$fn = 64;

// --- Parameters ---
rail_length = 300;
rail_width = 35;
rail_thickness = 15;

dovetail_top_width = 15;
dovetail_bottom_width = 25;
dovetail_depth = 7;

hole_diameter = 4.5;
countersink_diameter = 9.5;
countersink_depth = 4.5;
hole_positions = [30, 90, 150, 210, 270];

// --- Module ---
module wall_rail() {
    difference() {
        // Main body
        translate([0, -rail_width/2, 0])
            cube([rail_length, rail_width, rail_thickness]);
        
        // Dovetail slot cut
        translate([-1, 0, rail_thickness - dovetail_depth])
            rotate([90, 0, 90])
            linear_extrude(rail_length + 2)
            polygon([
                [-dovetail_bottom_width/2, -0.01],
                [dovetail_bottom_width/2, -0.01],
                [dovetail_top_width/2, dovetail_depth + 0.1],
                [-dovetail_top_width/2, dovetail_depth + 0.1]
            ]);
        
        // Mounting holes
        for (x = hole_positions) {
            // Main screw shaft
            translate([x, 0, -1])
                cylinder(d=hole_diameter, h=rail_thickness + 2);
            
            // Countersink for screw head
            translate([x, 0, rail_thickness - dovetail_depth - countersink_depth])
                cylinder(d1=hole_diameter, d2=countersink_diameter, h=countersink_depth + 0.01);
                
            // Clearance above countersink to ensure flush seating
            translate([x, 0, rail_thickness - dovetail_depth])
                cylinder(d=countersink_diameter, h=dovetail_depth + 1);
        }
    }
}

// --- Render ---
wall_rail();