bare/gpt-5-nano / tier-3-butt-hinge

```openscad
// OpenSCAD: 2 leaves + pin axis butt hinge (180° open state)

// Dimensions (mm)
leaf_w  = 25;
leaf_h  = 30;
leaf_t  = 2;

knuckle_d = 8;     // outer knuckle diameter
knuckle_r = knuckle_d/2;
pin_d     = 4;     // pin diameter
pin_r     = pin_d/2;
hole_d    = 4.6;   // inner hole diameter for knuckle/pin clearance (approx)
hole_r    = hole_d/2;

// Arrays defining knuckle positions along Y (as described)
left_knuckles_y  = [-12, 0, 12];   // 3 knuckles on left leaf (X ~ -4)
right_knuckles_y = [-6, 6];       // 2 knuckles on right leaf (X ~ +4)

left_holes_y  = [-12, 0, 12];      // interleaved knuckle holes on left (Y positions)
right_holes_y = [-6, 6];            // interleaved knuckle holes on right (Y positions)

// Base left leaf (X negative side)
module left_leaf() {
    difference() {
        // Base plate for left leaf: X from -25 to 0, Y from -15 to 15, Z from 0 to 2
        translate([-25, -15, 0])
            cube([25, 30, 2], center = false);

        // Left knuckles: cylindrical bosses (outer diameter 8 mm) along Y
        for (y = left_knuckles_y) {
            translate([-4, y, 1])
                rotate([90, 0, 0])
                    cylinder(h = 30, r = knuckle_r, center = true);
        }

        // Holes for pin along Y (inner diameter 4.6 mm)
        for (y = left_holes_y) {
            translate([0, y, 0])
                rotate([90, 0, 0])
                    cylinder(h = 30, r = hole_r, center = true);
        }

        // M3 mounting holes (approximate via simple through-hole cylinders)
        // 3 holes with 8 mm pitch along Y; using through holes (simplified)
        for (y = [-12, -4, 4]) {
            translate([0, y, 0])
                rotate([90, 0, 0])
                    cylinder(h = 30, r = 1.6, center = true);
        }
    }
}

// Base right leaf (X positive side)
module right_leaf() {
    difference() {
        // Base plate for right leaf: X from 0 to 25, Y -15 to 15, Z 0 to 2
        translate([0, -15, 0])
            cube([25, 30, 2], center = false);

        // Right knuckles: cylindrical bosses along Y
        for (y = right_knuckles_y) {
            translate([4, y, 1])
                rotate([90, 0, 0])
                    cylinder(h = 30, r = knuckle_r, center = true);
        }

        // Holes for pin along Y (inner diameter 4.6 mm)
        for (y = right_holes_y) {
            translate([0, y, 0])
                rotate([90, 0, 0])
                    cylinder(h = 30, r = hole_r, center = true);
        }

        // M3 mounting holes (simplified)
        for (y = [-6, 0, 6]) {
            translate([0, y, 0])
                rotate([90, 0, 0])
                    cylinder(h = 30, r = 1.6, center = true);
        }
    }
}

// Pin axis (along Y, centered at origin, length 32 mm to protrude 1 mm past each leaf)
module pin_axis() {
    // Cylinder along Y by rotating a Z-axis cylinder
    rotate([0, 0, 0])
        rotate([90, 0, 0])
            cylinder(h = 32, r = pin_r, center = true);
}

// Assemble hinge in 180° open state:
// - left leaf at X < 0
// - right leaf rotated 180° around hinge axis (Y) to lie in the same plane as left leaf (open state)
module hinge_open_state() {
    union() {
        left_leaf();
        // Opened state: rotate the right leaf around hinge axis (Y) by 180°
        rotate([0, 180, 0])
            right_leaf();
        // Pin passes through both leaves
        pin_axis();
    }
}

// Increase resolution for circles/arcs if desired
$fn = 60;

// Output final model
hinge_open_state();
```