iter-png-3/gpt-5.3-codex / tier-3-butt-hinge

```openscad
$fn = 96;

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

pin_d           = 4;
pin_r           = pin_d/2;
pin_len         = 32;    // 1mm protrusion each side from 30mm knuckle stack

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;      // -15

// ===== Utilities =====
function seg_center(i) = y0 + knuckle_seg*i + knuckle_seg/2; // i=0..4

left_idx  = [0,2,4]; // left leaf knuckles (outer, center, outer)
right_idx = [1,3];   // right leaf knuckles (middle two)

hole_y = [-8,0,8];   // 8mm pitch along Y

// ===== Features =====
module countersunk_hole_through(plate_t=2) {
    // Through hole
    translate([0,0,-plate_t/2-0.05])
        cylinder(h=plate_t+0.1, d=csk_thru_d);

    // Countersink from +Z surface (top): tapered, depth 1mm
    // top dia 6 -> bottom dia 3.2
    translate([0,0,plate_t/2-csk_depth])
        cylinder(h=csk_depth+0.01, d1=csk_thru_d, d2=csk_head_d);
}

module leaf_plate(side=1) {
    // side +1: right (x>0), side -1: left (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_half(yc, side=1) {
    // Half-cylinder shell centered at X=0, axis along Y, length=6
    intersection() {
        translate([0,yc,0])
            rotate([90,0,0])
                cylinder(h=knuckle_seg, d=knuckle_od, center=true);
        // keep x>=0 (right) or x<=0 (left)
        if (side>0)
            translate([0, yc-knuckle_seg/2-0.01, -knuckle_or-0.01])
                cube([knuckle_or+0.02, knuckle_seg+0.02, 2*knuckle_or+0.02], center=false);
        else
            translate([-knuckle_or-0.01, yc-knuckle_seg/2-0.01, -knuckle_or-0.01])
                cube([knuckle_or+0.02, knuckle_seg+0.02, 2*knuckle_or+0.02], center=false);
    }
}

module leaf_with_knuckles(side=1) {
    idxs = (side>0) ? right_idx : left_idx;

    difference() {
        union() {
            leaf_plate(side);
            for (i=idxs) knuckle_half(seg_center(i), side);
        }

        // Knuckle bore in each segment
        for (i=idxs) {
            translate([0,seg_center(i),0])
                rotate([90,0,0])
                    cylinder(h=knuckle_seg+0.2, d=knuckle_id, center=true);
        }

        // Screw holes near free edge
        hx = (side>0) ? (leaf_width_x-5) : (-leaf_width_x+5);
        for (yy=hole_y) {
            translate([hx,yy,0]) countersunk_hole_through(leaf_thick_z);
        }
    }
}

module pin() {
    // Pin axis on global Y axis
    rotate([90,0,0]) cylinder(h=pin_len, d=pin_d, center=true);
}

// ===== Assembly (180° open, both leaves coplanar) =====
union() {
    leaf_with_knuckles(-1); // left leaf to x<0
    leaf_with_knuckles( 1); // right leaf to x>0
    pin();
}
```