bare/claude-sonnet-4-6 / tier-3-butt-hinge

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

// Parameters
leaf_width  = 25;   // X direction (when open)
leaf_length = 30;   // Y direction (along pin)
leaf_thick  = 2;    // Z direction

pin_dia     = 4;
pin_r       = pin_dia / 2;
pin_length  = 32;   // 1mm overhang each end

knuckle_od  = 8;
knuckle_or  = knuckle_od / 2;
knuckle_id  = pin_dia + 0.3;  // 4.3mm  ← clearance bore
knuckle_ir  = knuckle_id / 2;
knuckle_h   = 6;    // each knuckle height

// Screw holes (M3 countersunk)
screw_cs_dia   = 6;
screw_cs_depth = 1;
screw_thru_dia = 3.2;
screw_count    = 3;
screw_pitch    = 8;   // Y spacing
// screw column is centred on leaf_length/2 in Y, spaced 8mm apart
// positions: -8, 0, +8  relative to leaf centre → 7, 15, 23 in Y

// Screw X position: middle of the leaf (away from knuckle side)
screw_x = -(leaf_width / 2);   // for left leaf  (negative side)

$fn = 48;

// ─────────────────────────────────────────────
// Helper: single countersunk hole (centred at origin, going -Z)
module cs_hole() {
    // countersink taper (cone, wider at top)
    cylinder(h = screw_cs_depth,
             r1 = screw_cs_dia / 2,
             r2 = screw_thru_dia / 2);
    // through hole
    translate([0, 0, -leaf_thick])
        cylinder(h = leaf_thick + screw_cs_depth + 0.01,
                 r = screw_thru_dia / 2);
}

// ─────────────────────────────────────────────
// Knuckle: a tube of height knuckle_h, centred at origin, axis = Z
module knuckle() {
    difference() {
        cylinder(h = knuckle_h, r = knuckle_or, center = true);
        cylinder(h = knuckle_h + 0.02, r = knuckle_ir, center = true);
    }
}

// ─────────────────────────────────────────────
// Left leaf  (x ≤ 0 side)
// Leaf flat face at z = 0, body goes to z = -leaf_thick
// Knuckles protrude above the flat face (z = 0 … knuckle_od/2 from axis)
// but we keep knuckle axis at x=0, z=0 and orient them along Y.
//
// Knuckle positions along Y (knuckle centres):
//   Left leaf  owns knuckles 1,3,5  → Y centres: 3, 15, 27  (0-indexed segments 0,2,4)
//   Right leaf owns knuckles 2,4    → Y centres: 9, 21       (segments 1,3)
//
// Knuckle axis is Y, so we rotate the tube 90° around X.

left_knuckle_y  = [3, 15, 27];   // centres in Y for left leaf
right_knuckle_y = [9, 21];       // centres in Y for right leaf

// The leaf starts at Y=0 and ends at Y=leaf_length (30).
// Knuckle outer radius sits on the x=0 line; leaf extends to x = -leaf_width.

module left_leaf() {
    difference() {
        union() {
            // flat plate
            translate([-leaf_width, 0, -leaf_thick])
                cube([leaf_width, leaf_length, leaf_thick]);

            // knuckles (rotated 90° so axis is Y)
            for (yc = left_knuckle_y) {
                translate([0, yc, 0])
                    rotate([90, 0, 0])
                        knuckle();
            }
        }

        // countersunk screw holes — placed on the leaf, away from knuckle side
        // X centre at -leaf_width/2, Y positions centred on leaf
        for (i = [0 : screw_count - 1]) {
            ypos = (leaf_length - (screw_count - 1) * screw_pitch) / 2
                   + i * screw_pitch;
            translate([-leaf_width / 2, ypos, 0])
                cs_hole();
        }
    }
}

module right_leaf() {
    difference() {
        union() {
            // flat plate
            translate([0, 0, -leaf_thick])
                cube([leaf_width, leaf_length, leaf_thick]);

            // knuckles
            for (yc = right_knuckle_y) {
                translate([0, yc, 0])
                    rotate([90, 0, 0])
                        knuckle();
            }
        }

        // countersunk screw holes
        for (i = [0 : screw_count - 1]) {
            ypos = (leaf_length - (screw_count - 1) * screw_pitch) / 2
                   + i * screw_pitch;
            translate([leaf_width / 2, ypos, 0])
                cs_hole();
        }
    }
}

// ─────────────────────────────────────────────
// Pin: along Y axis, centred so it overhangs 1mm at each end
module pin() {
    translate([0, -1, 0])          // shift so Y=-1 … Y=31
        rotate([-90, 0, 0])
            cylinder(h = pin_length, r = pin_r);
}

// ─────────────────────────────────────────────
// Assembly — 180° open: both leaves in the same Z=0 plane
color("silver", 0.9) left_leaf();
color("silver", 0.9) right_leaf();
color("gold",   1.0) pin();
```