$fn=64;

// --- Parameters ---
columns = 5;            // Number of columns (5x2 = 10 tubes)
rows = 2;               // Number of rows
tube_diameter = 26;     // Fits standard 20-25ml paint tubes/droppers
hole_depth = 25;        // How deep the tubes sit in the rack
wall_thickness = 4;     // Minimum plastic thickness between holes
base_thickness = 3;     // Thickness of the floor under the tubes
step_height = 15;       // Elevation difference between rows

// --- Calculated Variables ---
spacing = tube_diameter + wall_thickness;
rack_width = (columns * spacing) + wall_thickness;
row_depth = spacing + wall_thickness;

// --- Geometry ---
difference() {
    // Main solid body (stepped)
    union() {
        for (y = [0 : rows - 1]) {
            translate([0, y * spacing, 0])
                cube([
                    rack_width, 
                    row_depth, 
                    hole_depth + base_thickness + (y * step_height)
                ]);
        }
    }

    // Subtract tube holder holes
    for (x = [0 : columns - 1]) {
        for (y = [0 : rows - 1]) {
            cx = wall_thickness + (tube_diameter / 2) + (x * spacing);
            cy = wall_thickness + (tube_diameter / 2) + (y * spacing);
            cz = base_thickness + (y * step_height);

            translate([cx, cy, cz])
                cylinder(h = hole_depth + 1, d = tube_diameter);
        }
    }
}