Soviet PO-2 concrete (Lachman pattern)

/*
 * Hexagonal Box with Soviet PO-2 Fence Design (Version 11)
 * Corrected waffle pattern geometry using robust hull() primitives with shifted top ridge
 * Zero flat spacing between cells (extrapolated base sizes)
 * Blocks are exactly square, spanning the full window width (no ugly side paddings)
 * Concrete gray color styling
 * Perfect 120-degree bevel joints on the outer frame to eliminate V-notches
 * 45-degree chamfered inner frame edges to eliminate support-requiring overhangs
 * Adaptable for 3D printing (supports-free stacking joints)
 */

/* [Hexagonal Box Dimensions] */
// Maximum outer diameter of the hexagon (vertex-to-vertex) in mm
D_max = 250; // [100:5:300]
// Height of the box in mm
H = 105; // [30:5:200]
// Nominal wall thickness at the frame in mm
wall_thickness = 6.0; // [4.0:0.5:10.0]
// Add a solid floor at the bottom of the box
has_bottom = false;

/* [PO-2 Waffle Grid Pattern] */
// Number of columns of waffle pyramids per face (5 matches ref-pattern-3.png)
panel_cols = 5; // [4:1:16]
// Number of rows of waffle pyramids per face (4 matches ref-pattern-3.png)
panel_rows = 4; // [2:1:8]
// Minimum width of the border frame around each panel in mm
border_w = 6.0; // [3.0:0.5:12.0]
// Width of the grooves between waffle cells in mm (0.0 for sharp V-grooves)
groove_w = 0.0; // [0.0:0.1:3.0]
// Depth/height of the waffle pyramids in mm
pyramid_height = 2.0; // [1.0:0.1:5.0]
// Proportional length of the horizontal flat top ridge (0.0 to 1.0)
pyramid_top_ratio = 0.5; // [0.1:0.05:0.9]
// Vertical shift of the top ridge relative to cell height (0.167 gives 33% / 66% split)
pyramid_shift = 0.167; // [-0.3:0.01:0.3]

/* [Stacking Joint Parameters] */
// Height of the stacking ridge in mm
j_height = 3.0; // [2.0:0.1:5.0]
// Width of the stacking ridge in mm
j_width = 2.4; // [1.0:0.1:5.0]
// Chamfer size on the stacking ridge for easy alignment in mm
j_chamfer = 0.6; // [0.2:0.1:1.5]
// Clearance between top lip and bottom groove in mm
clearance = 0.2; // [0.05:0.05:0.5]

/* [Hidden] */
frame_height = 1.5;

// Derived geometry calculations
R_outer = D_max / 2;
R_face = R_outer * cos(30);
W = R_outer;

module po2_waffle_cell(cell_w, cell_h, pyr_h, top_w) {
    base_depth = 0.5; // Overlap depth into the base wall to prevent coplanar rendering artifacts
    z_shift = cell_h * pyramid_shift;
    
    // Extrapolate base size so that the cell size is exactly cell_w x cell_h at X = 0
    w_base = cell_w + base_depth * (cell_w - top_w) / pyr_h;
    h_base = cell_h * (1 + base_depth / pyr_h);
    
    hull() {
        // Base plate (at X = -base_depth)
        translate([-base_depth, -w_base/2, -h_base/2])
            cube([0.01, w_base, h_base]);
        
        // Top line segment (at X = pyr_h, shifted in Z)
        translate([pyr_h, -top_w/2, z_shift - 0.005])
            cube([0.01, top_w, 0.01]);
    }
}

module top_lip() {
    translate([0, 0, H])
    rotate([90, 0, 0])
    linear_extrude(height = W + 20, center = true) {
        polygon([
            [-wall_thickness/2 - j_width/2, 0],
            [-wall_thickness/2 - j_width/2 + j_chamfer, j_height],
            [-wall_thickness/2 + j_width/2 - j_chamfer, j_height],
            [-wall_thickness/2 + j_width/2, 0]
        ]);
    }
}

module bottom_groove() {
    h_recess = j_height + clearance + 0.1;
    w_recess = j_width + 2 * clearance;
    entry_chamfer = j_chamfer;
    
    rotate([90, 0, 0])
    linear_extrude(height = W + 20, center = true) {
        polygon([
            [-wall_thickness/2 - w_recess/2 - entry_chamfer, -0.1],
            [-wall_thickness/2 - w_recess/2, entry_chamfer],
            [-wall_thickness/2 - w_recess/2, h_recess],
            [-wall_thickness/2 + w_recess/2, h_recess],
            [-wall_thickness/2 + w_recess/2, entry_chamfer],
            [-wall_thickness/2 + w_recess/2 + entry_chamfer, -0.1]
        ]);
    }
}

module single_face() {
    // cell_size is determined solely by the width of the window, so they span it exactly
    W_win = W - 2 * border_w;
    cell_size = W_win / panel_cols;
    
    cell_w = cell_size;
    cell_h = cell_size;
    
    grid_w = W_win;
    grid_h = panel_rows * cell_size;
    
    difference() {
        union() {
            // Base wall
            translate([-wall_thickness, -W/2, 0])
                cube([wall_thickness, W, H]);
            
            // Raised border frame (extra width added so bevel cut resolves perfectly at corners)
            difference() {
                translate([0, -W/2 - 5, 0])
                    cube([frame_height, W + 10, H]);
                
                // 45-degree chamfered window cutout matching the grid size
                hull() {
                    // Back sheet (X = -2)
                    w_back = grid_w - 2 * frame_height - 4;
                    h_back = grid_h - 2 * frame_height - 4;
                    translate([-2, -w_back/2, H/2 - h_back/2])
                        cube([0.01, w_back, h_back]);
                    
                    // Front sheet (X = frame_height + 2)
                    w_front = grid_w + 4;
                    h_front = grid_h + 4;
                    translate([frame_height + 2, -w_front/2, H/2 - h_front/2])
                        cube([0.01, w_front, h_front]);
                }
            }
            
            // Waffle grid
            pyr_base_w = cell_w - groove_w;
            pyr_base_h = cell_h - groove_w;
            
            for (c = [0 : panel_cols - 1]) {
                for (r = [0 : panel_rows - 1]) {
                    y_pos = -grid_w/2 + (c + 0.5) * cell_w;
                    z_pos = H/2 - grid_h/2 + (r + 0.5) * cell_h;
                    translate([0, y_pos, z_pos])
                        po2_waffle_cell(pyr_base_w, pyr_base_h, pyramid_height, pyr_base_w * pyramid_top_ratio);
                }
            }
            
            // Top lip (male joint)
            top_lip();
        }
        
        // Subtract bottom groove (female joint)
        bottom_groove();
    }
}

module bevel_hull(h, wall_t, R_out, relief_h) {
    linear_extrude(height = h) {
        polygon([
            [-wall_t, -W/2 + wall_t * tan(30)],
            [relief_h, -W/2 - relief_h * tan(30)],
            [relief_h, W/2 + relief_h * tan(30)],
            [-wall_t, W/2 - wall_t * tan(30)]
        ]);
    }
}

module beveled_face() {
    intersection() {
        single_face();
        bevel_hull(H + j_height + 1, wall_thickness, W, pyramid_height + 2);
    }
}

// Assemble the hexagonal box in concrete gray color
color("LightGrey") {
    union() {
        for (i = [0 : 5]) {
            rotate([0, 0, i * 60])
                translate([R_face, 0, 0])
                    beveled_face();
        }
        
        // Optional bottom floor
        if (has_bottom) {
            r_in = R_face - wall_thickness;
            R_inner = r_in / cos(30);
            translate([0, 0, j_height + clearance])
                rotate([0, 0, 30])
                    cylinder(r = R_inner, h = 2.0, $fn = 6);
        }
    }
}