$fn=64;

// --- Parameters ---
rows = 4;
cols = 8;
bit_hole_diameter = 7.4;  // Clearance for standard 1/4" (6.35mm) hex bits
hole_depth = 15;
base_thickness = 4;
hole_spacing = 12;        // Center-to-center distance between bits
edge_margin = 8;          // Distance from edge to first hole center
corner_radius = 3;        // Radius of the block's rounded corners

// --- Calculated Dimensions ---
block_width = (cols - 1) * hole_spacing + (2 * edge_margin);
block_depth = (rows - 1) * hole_spacing + (2 * edge_margin);
block_height = hole_depth + base_thickness;

// --- Model ---
difference() {
    // Main Body
    hull() {
        for (x = [corner_radius, block_width - corner_radius]) {
            for (y = [corner_radius, block_depth - corner_radius]) {
                translate([x, y, 0])
                    cylinder(r = corner_radius, h = block_height);
            }
        }
    }

    // Bit Holes & Chamfers
    for (r = [0 : rows - 1]) {
        for (c = [0 : cols - 1]) {
            translate([
                edge_margin + (c * hole_spacing),
                edge_margin + (r * hole_spacing),
                base_thickness
            ]) {
                // Main cylindrical hole for the bit
                cylinder(h = hole_depth + 1, d = bit_hole_diameter);
                
                // Top chamfer for easier bit insertion
                translate([0, 0, hole_depth - 1.5])
                    cylinder(h = 1.51, d1 = bit_hole_diameter, d2 = bit_hole_diameter + 2.5);
            }
        }
    }
}