$fn = 64;

// --- Parameters ---
rail_length = 500;
rail_width = 40;
rail_depth = 15;

// Dovetail settings
dt_bottom_w = 26;
dt_top_w = 16;
dt_depth = 8;

// Mounting hole settings
hole_spacing = 100;
hole_start = 50;
screw_shaft_d = 5;
screw_head_d = 10;
countersink_h = 3;

difference() {
    // Main Rail Body
    cube([rail_length, rail_width, rail_depth]);

    // Dovetail Cutout
    // Profile is drawn in XY, extruded along Z, then rotated to run along X
    translate([-1, rail_width / 2, rail_depth - dt_depth])
    rotate([0, 90, 0])
    linear_extrude(height = rail_length + 2)
    polygon([
        [0, -dt_bottom_w / 2],
        [0, dt_bottom_w / 2],
        [-dt_depth - 0.1, dt_top_w / 2],
        [-dt_depth - 0.1, -dt_top_w / 2]
    ]);

    // Mounting Holes
    for (x = [hole_start : hole_spacing : rail_length - 1]) {
        translate([x, rail_width / 2, -0.1]) {
            // Screw shaft
            cylinder(h = rail_depth + 0.2, d = screw_shaft_d);

            // Countersink for screw head
            translate([0, 0, rail_depth - dt_depth - countersink_h + 0.1])
            cylinder(h = countersink_h, d1 = screw_shaft_d, d2 = screw_head_d);

            // Clearance for screw head inside the dovetail slot
            translate([0, 0, rail_depth - dt_depth + 0.1])
            cylinder(h = dt_depth + 0.2, d = screw_head_d);
        }
    }
}