iter-png-3/claude-sonnet-4-6 / tier-3-butt-hinge

画像を確認して気づいた問題点：

1. **ナックルが1本の大きな円柱になっている** – 左3個・右2個の互い違い配置になっておらず、全体が繋がった1本の筒に見える。`knuckle_base_fill` の `hull()` が Y 方向に連続してしまっているのが原因。
2. **ピンが片側(Y=0側)しか飛び出ていない** – 両端 1mm ずつ飛び出るべきだが、片端しか見えない。
3. **右板のナックルが見えない** – ナックル間の隙間が表現されていない。
4. **`knuckle_base_fill` の `linear_extrude` の軸方向が誤り** – rotate と linear_extrude の組み合わせが意図通りでない。

修正方針：`knuckle_base_fill` を `hull()` + 正しい押し出しで作り直し、各ナックルを独立した個体として明確に分離します。

```openscad
// Butt Hinge - 180° open position
// Pin axis along Y, leaves extend in -X and +X directions

$fn = 64;

// Parameters
leaf_width  = 25;
leaf_length = 30;
leaf_thick  = 2;

pin_dia    = 4;
pin_r      = pin_dia / 2;
pin_length = 32;

knuckle_od = 8;
knuckle_or = knuckle_od / 2;
knuckle_id = pin_dia + 0.3;
knuckle_ir = knuckle_id / 2;
knuckle_h  = 6;

// Knuckle Y start positions (each 6mm segment)
// Left leaf  (3 knuckles): segments 0,2,4 → Y start 0, 12, 24
// Right leaf (2 knuckles): segments 1,3   → Y start 6, 18
left_knuckle_y_starts  = [0, 12, 24];
right_knuckle_y_starts = [6, 18];

// Pin axis is at Z = knuckle_or above plate top face (Z=0)
knuckle_z = knuckle_or;

// Screw holes (M3 countersunk)
screw_cs_dia   = 6;
screw_cs_depth = 1;
screw_thru_dia = 3.2;
screw_count    = 3;
screw_pitch    = 8;

function screw_y(i) =
    (leaf_length - (screw_count - 1) * screw_pitch) / 2 + i * screw_pitch;

// ─────────────────────────────────────────────
// Single knuckle: cylinder + web connecting it to the plate
// y0 = Y start of this 6mm segment
module single_knuckle(y0) {
    yc = y0 + knuckle_h / 2;   // centre of knuckle in Y

    // Knuckle tube
    translate([0, yc, knuckle_z])
        rotate([90, 0, 0])
            difference() {
                cylinder(h = knuckle_h, r = knuckle_or, center = true);
                cylinder(h = knuckle_h + 0.1, r = knuckle_ir, center = true);
            }

    // Web / gusset: hull between flat plate rect and knuckle circle,
    // extruded along Y for the length of this knuckle
    translate([0, y0, 0])
        linear_extrude(height = knuckle_h)
            hull() {
                // footprint at plate top (Z=0): thin wide rect
                translate([0, 0])
                    square([knuckle_od, 0.01], center = true);
                // knuckle cross-section at axis height
                translate([0, knuckle_z])
                    circle(r = knuckle_or);
            }
}

// ─────────────────────────────────────────────
// Countersunk hole, opening at Z=0, going into -Z
module cs_hole() {
    // Countersink cone (wide at top, narrow at bottom)
    translate([0, 0, 0.01])
        cylinder(h = screw_cs_depth + 0.01,
                 r1 = screw_cs_dia / 2,
                 r2 = screw_thru_dia / 2,
                 $fn = 32);
    // Through shaft
    translate([0, 0, -(leaf_thick + 0.01)])
        cylinder(h = leaf_thick + screw_cs_depth + 0.02,
                 r = screw_thru_dia / 2,
                 $fn = 32);
}

// ─────────────────────────────────────────────
// Left leaf
module left_leaf() {
    difference() {
        union() {
            // Flat plate (extends in -X)
            translate([-leaf_width, 0, -leaf_thick])
                cube([leaf_width, leaf_length, leaf_thick]);

            // 3 knuckles
            for (y0 = left_knuckle_y_starts)
                single_knuckle(y0);
        }

        // Screw holes on the plate (centred in X over plate)
        for (i = [0 : screw_count - 1])
            translate([-leaf_width / 2, screw_y(i), 0])
                cs_hole();

        // Pin bore along entire Y span
        translate([0, -1, knuckle_z])
            rotate([-90, 0, 0])
                cylinder(h = pin_length + 2, r = knuckle_ir);
    }
}

// ─────────────────────────────────────────────
// Right leaf
module right_leaf() {
    difference() {
        union() {
            // Flat plate (extends in +X)
            translate([0, 0, -leaf_thick])
                cube([leaf_width, leaf_length, leaf_thick]);

            // 2 knuckles
            for (y0 = right_knuckle_y_starts)
                single_knuckle(y0);
        }

        // Screw holes
        for (i = [0 : screw_count - 1])
            translate([leaf_width / 2, screw_y(i), 0])
                cs_hole();

        // Pin bore
        translate([0, -1, knuckle_z])
            rotate([-90, 0, 0])
                cylinder(h = pin_length + 2, r = knuckle_ir);
    }
}

// ─────────────────────────────────────────────
// Pin: Y from -1 to +31 (1mm overhang each end: 0..30 + margins)
module pin() {
    translate([0, -1, knuckle_z])
        rotate([-90, 0, 0])
            cylinder(h = pin_length, r = pin_r);
}

// ─────────────────────────────────────────────
// Assembly
color([0.75, 0.75, 0.78]) left_leaf();
color([0.75, 0.75, 0.78]) right_leaf();
color([0.85, 0.70, 0.20]) pin();
```