iter-png-2/gpt-5.4-nano / tier-3-butt-hinge

```openscad
// Small butt hinge (3 parts assembled) in open position (180deg)

$fn = 96;

// ---- Parameters ----
t = 2;                 // leaf thickness (Z)
Ylen = 30;             // leaf length along hinge axis (Y)
Xspan = 25;            // leaf length along opening direction (X)
pin_d = 4;
pin_len = 32;          // total pin length (centered)

knuckle_len = 30;     // along Y
knuckle_segments = 5; // split into 6mm each (=> 6mm)
seg = knuckle_len/knuckle_segments; // 6mm (not strictly required further)

clear = 0.3;
bore_d = pin_d + clear; // 4.6mm

kn_outer = 8;
kn_inner = bore_d;

gap = 0.2;             // boolean robustness

// M3 countersunk holes (3 pcs per leaf)
cs_d_top = 6;         // countersink cone top diameter (mm)
cs_depth = 1;         // countersink depth (mm)
through_d = 3.2;     // through hole diameter (mm)
hole_ys = [8, 16, 24];// pitch 8mm along Y

// ---- Helper: cylinder whose axis is along Y ----
module cyl_y(d=1, h=1, center=true) {
    rotate([90,0,0]) cylinder(d=d, h=h, center=center);
}

// Leaf plate centered on hinge plane at X=0.
// It lies in YZ plane when centered at X=0? In this model: create as XY-plane leaf with Z thickness.
module leaf_plate(x_sign=1) {
    // leaf on x<0 or x>0; flat faces are parallel to X-Y plane, thickness along Z
    translate([x_sign * (Xspan/2), 0, 0])
        cube([Xspan, Ylen, t], center=true);
}

// Knuckle sleeve along Y at X=0, centered at given y.
// Bore is along Y.
module knuckle(y_pos=0) {
    difference() {
        translate([0, y_pos, 0])
            cyl_y(d=kn_outer, h=knuckle_len, center=true);
        translate([0, y_pos, 0])
            cyl_y(d=kn_inner, h=knuckle_len + 2*gap, center=true);
    }
}

// Countersunk + through hole along Z axis, centered at current origin.
// Countersink is cut from +Z face (and will still be valid as subtraction).
module m3_hole_z() {
    // through
    cylinder(d=through_d, h=t + 6*gap, center=true);

    // countersink cone: top diameter cs_d_top at +Z face
    // We place cone center so that its base aligns at z=+t/2 (plate top).
    // Cone height = cs_depth.
    translate([0,0, (t/2 - cs_depth/2)])
        cylinder(h=cs_depth, d1=cs_d_top, d2=through_d, center=true);
}

// One leaf with knuckles and screw holes; knuckle bores for pin are subtracted here,
// but since the other leaf also subtracts, this is safe (shared hole remains).
module leaf_with_knuckles_and_holes(x_sign=1, kn_positions=[]) {
    difference() {
        union() {
            leaf_plate(x_sign);

            // knuckles at X=0 plane
            for (y in kn_positions)
                knuckle(y);
        }

        // Subtract the pin bore through the knuckles for this leaf
        for (y in kn_positions)
            translate([0, y, 0])
                cyl_y(d=kn_inner, h=kn_outer + 4*gap, center=true);

        // Subtract 3 M3 screw holes at far side from knuckles.
        // "far side away from knuckle" => leaf face at x = x_sign*(Xspan/2)
        // Hole axis is along Z at that x location.
        for (yy in hole_ys) {
            translate([x_sign * (Xspan/2), yy, 0])
                rotate([90,0,0]) {
                    // no rotation; m3_hole_z expects axis along Z at its own position
                    // (keep as-is)
                }
            translate([x_sign * (Xspan/2), yy, 0])
                m3_hole_z();
        }
    }
}

// Pin: cylinder along Y
module pin() {
    cyl_y(d=pin_d, h=pin_len, center=true);
}

// ---- Knuckle Y positions ----
// centers at Y = -12, -6, 0, 6, 12 spanning 30mm with 6mm steps
kn_centers = [-12, -6, 0, 6, 12];

// Left: outer 2 + central 1 => [-12, 0, 12]
// Right: middle 2 => [-6, 6]
left_kn = [kn_centers[0], kn_centers[2], kn_centers[4]];
right_kn = [kn_centers[1], kn_centers[3]];

// ---- Assembly in open position (180deg) ----
module butt_hinge_open180() {
    union() {
        leaf_with_knuckles_and_holes(x_sign=-1, kn_positions=left_kn);
        leaf_with_knuckles_and_holes(x_sign= 1, kn_positions=right_kn);

        pin();
    }
}

butt_hinge_open180();
```