bare/gpt-5.3-codex / tier-3-butt-hinge

```openscad
$fn = 96;

// ===== Parameters =====
leaf_len_y      = 30;    // along hinge axis
leaf_width_x    = 25;    // opening direction
leaf_thick_z    = 2;

pin_d           = 4;
pin_r           = pin_d/2;
pin_len         = 32;

knuckle_od      = 8;
knuckle_or      = knuckle_od/2;
knuckle_id      = 4.6;   // pin + 0.3 clearance
knuckle_ir      = knuckle_id/2;
knuckle_seg     = 6;     // 30/5

csk_thru_d      = 3.2;
csk_head_d      = 6;
csk_depth       = 1;

y0 = -leaf_len_y/2;      // start of knuckle stack (-15)
z_face = leaf_thick_z/2; // plates occupy z in [-1, +1]

// Knuckle segment centers (5 equal 6mm segments across 30mm)
function seg_center(i) = y0 + knuckle_seg*i + knuckle_seg/2;

// Left leaf has segments: 0,2,4
left_idx  = [0,2,4];
// Right leaf has segments: 1,3
right_idx = [1,3];

// Screw hole Y positions (8mm pitch, centered)
hole_y = [-8, 0, 8];

// ===== Modules =====
module countersunk_hole(z0, z1) {
    // through hole
    translate([0,0,z0-0.1])
        cylinder(h=(z1-z0)+0.2, r=csk_thru_d/2);

    // tapered countersink from top surface
    // top diameter 6, bottom diameter 3.2, depth 1
    translate([0,0,z1-csk_depth])
        cylinder(h=csk_depth+0.01, r1=csk_thru_d/2, r2=csk_head_d/2);
}

module leaf_base(side=1) {
    // side=+1 => right leaf (x>0), side=-1 => left leaf (x<0)
    x0 = (side > 0) ? 0 : -leaf_width_x;
    translate([x0, y0, -leaf_thick_z/2])
        cube([leaf_width_x, leaf_len_y, leaf_thick_z], center=false);
}

module knuckle_shell(yc, side=1) {
    // Outer knuckle body attached to leaf edge at x=0
    intersection() {
        translate([0, yc, 0])
            rotate([90,0,0])
                cylinder(h=knuckle_seg, r=knuckle_or, center=true);
        // keep half by side
        translate([(side>0)?0:-knuckle_or, yc-knuckle_seg/2-0.01, -knuckle_or-0.01])
            cube([knuckle_or, knuckle_seg+0.02, 2*knuckle_or+0.02], center=false);
    }
}

module leaf_with_knuckles(side=1) {
    difference() {
        union() {
            leaf_base(side);

            idxs = (side > 0) ? right_idx : left_idx;
            for (i = idxs)
                knuckle_shell(seg_center(i), side);
        }

        // knuckle bore (only where material exists)
        for (i = (side > 0) ? right_idx : left_idx) {
            translate([0, seg_center(i), 0])
                rotate([90,0,0])
                    cylinder(h=knuckle_seg+0.2, r=knuckle_ir, center=true);
        }

        // 3 countersunk holes near free edge of each leaf
        hx = (side > 0) ? (leaf_width_x - 5) : (-leaf_width_x + 5);
        for (yy = hole_y) {
            translate([hx, yy, 0])
                countersunk_hole(-leaf_thick_z/2, leaf_thick_z/2);
        }
    }
}

module pin_axis() {
    translate([0, 0, 0])
        rotate([90,0,0])
            cylinder(h=pin_len, r=pin_r, center=true);
}

// ===== Assembly (180° open) =====
union() {
    leaf_with_knuckles(-1); // left, x<0
    leaf_with_knuckles( 1); // right, x>0
    pin_axis();
}
```