bare-low/claude-fable-5-1 / tier-3-butt-hinge

```openscad
// Small butt hinge for furniture — open 180°
// Pin axis = Y axis (+Y), leaves lie in Z-normal plane

$fn = 64;

// ---------- parameters ----------
leaf_len   = 30;   // along Y (hinge axis)
leaf_w     = 25;   // along X (opening direction)
leaf_t     = 2;    // thickness (Z)

pin_d      = 4;
pin_len    = 32;
clearance  = 0.3;
kn_od      = 8;
kn_id      = pin_d + clearance;   // 4.6
kn_seg     = leaf_len / 5;        // 6 mm

hole_pitch = 8;
hole_d     = 3.2;
csk_d      = 6;
csk_depth  = 1;
hole_x     = 18;   // distance from pin axis to screw line

// ---------- helpers ----------
module knuckle(y0, y1) {
    // cylinder along Y from y0 to y1, centered on X=0, Z=0
    translate([0, y0, 0])
        rotate([-90, 0, 0])
            cylinder(d = kn_od, h = y1 - y0);
}

module pin_bore() {
    translate([0, -1, 0])
        rotate([-90, 0, 0])
            cylinder(d = kn_id, h = leaf_len + 2);
}

module screw_hole() {
    // through hole + countersink on top face (+Z)
    union() {
        translate([0, 0, -1])
            cylinder(d = hole_d, h = leaf_t + 2);
        translate([0, 0, leaf_t - csk_depth])
            cylinder(d1 = hole_d, d2 = csk_d, h = csk_depth + 0.01);
        translate([0, 0, leaf_t - 0.001])
            cylinder(d = csk_d, h = 1);
    }
}

// Generic leaf; sgn = -1 for left (x<0), +1 for right (x>0)
// segs = list of knuckle segment indices (0..4)
module leaf(sgn, segs) {
    difference() {
        union() {
            // plate: from knuckle to outer edge, top face at Z=leaf_t/2
            translate([sgn > 0 ? 0 : -leaf_w, 0, -leaf_t / 2])
                cube([leaf_w, leaf_len, leaf_t]);
            // knuckles
            for (i = segs)
                knuckle(i * kn_seg, (i + 1) * kn_seg);
        }
        // pin bore
        pin_bore();
        // gap cuts between knuckles (so adjacent segments don't touch)
        for (i = [0 : 4])
            if (len(search(i, segs)) == 0)
                translate([-kn_od, i * kn_seg - 0.15, -kn_od])
                    cube([2 * kn_od, kn_seg + 0.3, 2 * kn_od]);
        // screw holes
        for (j = [-1, 0, 1])
            translate([sgn * hole_x, leaf_len / 2 + j * hole_pitch, -leaf_t / 2])
                screw_hole();
    }
}

module pin() {
    translate([0, -1, 0])
        rotate([-90, 0, 0])
            cylinder(d = pin_d, h = pin_len);
}

// ---------- assembly (open 180°) ----------
color("silver")     leaf(-1, [0, 2, 4]);  // left leaf: outer 2 + center
color("lightgray")  leaf( 1, [1, 3]);     // right leaf: middle 2
color("gold")       pin();
```