bare/gemma-4-e4b / tier-3-butt-hinge

```openscad
// ======================================================
// Furniture Butt Hinge Model (180 Degrees Open)
// Components: Left Leaf, Right Leaf, Pin Axis
// Dimensions: 30x25 leaf, D4 pin, 2mm thickness.
// ======================================================

// --- Global Parameters ---
LEAF_WIDTH = 25;   // Width along X axis
LEAF_HEIGHT = 30;  // Height along Y axis
THICKNESS = 2;     // Thickness along Z axis
PIN_DIA = 4;       // Pin diameter
KNUCKLE_OUTER_DIA = 8;
KNUCKLE_INNER_DIA = PIN_DIA + 0.3; // 4.3mm clearance hole

// Screw parameters (M3)
SCREW_DIAMETER_THROUGH = 3.2; // mm
SCREW_DEPTH_COUNTERBORE = 1;   // mm
SCREW_COUNTERBORE_DIA = 6;     // mm

// Y-coordinates for knuckle centers
KNUCKLE_Y_L = [-12, 0, 12];    // Left Leaf (Outer 2 + Center 1)
KNUCKLE_Y_R = [-6, 6];         // Right Leaf (Intermediate 2)

// Y-coordinates for screw holes (3 spots, approx 8mm pitch spacing)
SCREW_Y_POSITIONS = [-10, 0, 10];


// ======================================================
// 1. Pin Axis Component
// ======================================================
module pin_axis() {
    translate([0, 0, -(THICKNESS/2)]) {
        cylinder(h=LEAF_HEIGHT + 4, r=PIN_DIA/2, $fn=60);
    }
}

// ======================================================
// 2. Single Leaf Module (Handles the basic shape and cutouts)
// @param is_left: True if this leaf should be modeled for the left side (X<0).
//               False if for the right side (X>0).
// @param knuckles_y: Array of Y coordinates for knuckle placement.
module hinged_leaf(is_left = true, knuckles_y, screws_y) {

    // Determine translation offset based on position
    translate([-(LEAF_WIDTH/2) * (if(is_left)) : 1, 0, 0]) {
        color([0.4, 0.2, 0.1]) { // Brownish color for wood look
            difference() {
                // A. Base Block (The solid leaf)
                cube([LEAF_WIDTH, LEAF_HEIGHT, THICKNESS]);

                // B. Cutouts to make space for knuckles and screws
                union() {
                    // 1. Knuckle Holes (These holes must pass through the center axis Y=0)
                    for (y = knuckles_y) {
                        translate([0, y, -(THICKNESS/2)]) {
                            cylinder(h=THICKNESS + 0.1, r=(KNUCKLE_OUTER_DIA/2) + 0.5, $fn=60); // Slightly larger to guarantee removal
                        }
                    }

                    // 2. Screw Holes (3 spots per leaf)
                    for (y = screws_y) {
                         translate([0, y, -(THICKNESS/2)]) {
                            // Counterbore cut (D=6mm, Depth=1mm)
                            cylinder(h=SCREW_DEPTH_COUNTERBORE + 0.1, r=(SCREW_COUNTERBORE_DIA/2), $fn=36);

                            // Through hole (Must pass through the full thickness)
                            translate([0, y, SCREW_DEPTH_COUNTERBORE]) {
                                cylinder(h=THICKNESS + 0.1, r=(SCREW_DIAMETER_THROUGH/2), $fn=36);
                            }
                        }
                    }

                    // 3. Pin Axis Clearance (Must pass through all knuckles)
                    // This cutout ensures the central pin can rotate freely while leaving structural integrity around knuckle centers.
                    translate([0, -15, -(THICKNESS/2)]) { // Start slightly outside Y range to ensure full passage
                        cylinder(h=LEAF_HEIGHT + 3, r=(KNUCKLE_INNER_DIA / 2) + 0.3, $fn=60);
                    }

                }
            }
        }
    }
}


// ======================================================
// ASSEMBLY AND DISPLAY (180 Degree Open State)
// ======================================================

// Use a union to display all parts together in the final open configuration.
union() {

    // 1. Left Leaf (X < 0 side)
    // Knuckles: Y=-12, 0, 12
    hinged_leaf(is_left = true, knuckles_y = KNUCKLE_Y_L, screws_y = SCREW_Y_POSITIONS);

    // 2. Right Leaf (X > 0 side)
    // Knuckles: Y=-6, 6
    hinged_leaf(is_left = false, knuckles_y = KNUCKLE_Y_R, screws_y = SCREW_Y_POSITIONS);

    // 3. Pin Axis (Central Pivot)
    pin_axis();
}
```