/* [Knob Dimensions] */
outer_diameter = 30;           // [20:1:60]
total_height = 14;             // [8:1:30]
top_fillet_radius = 2.0;       // [0.5:0.5:5]
knurl_depth = 0.75;            // [0.3:0.05:1.5]
knurl_count = 42;              // [20:2:80]
knurl_helix_angle = 45;        // [30:5:60]

/* [Nut & Bolt Dimensions] */
bolt_diameter = 6.5;           // [3:0.1:12]
hex_nut_flats = 10.0;          // [5:0.1:20]
hex_nut_depth = 5.0;           // [2:0.5:15]

/* [Finishing & Aesthetics] */
knob_color = "DimGray";
nut_preview = true;
nut_color = "Gold";
$fn = 72;

// Calculated values
radius = outer_diameter / 2;
// Across flats (W) to across corners (C) for a regular hexagon: C = W / cos(30) = W * 2 / sqrt(3)
hex_nut_radius = (hex_nut_flats / 2) / cos(30);

// Knurl twist angle based on height and circumference for the chosen helix angle
circumference = 3.14159265 * outer_diameter;
twist_deg = (total_height * tan(knurl_helix_angle) / circumference) * 360;

module knurl_profile_2d() {
    polygon([
        for (i = [0 : 2 * knurl_count - 1])
            let(
                angle = i * 180 / knurl_count,
                r = (i % 2 == 0) ? radius : (radius - knurl_depth)
            )
            [r * cos(angle), r * sin(angle)]
    ]);
}

module diamond_knurl_cylinder(h) {
    slices = ceil(h * 3);
    intersection() {
        linear_extrude(height = h, twist = twist_deg, slices = slices, convexity = 10)
            knurl_profile_2d();
        linear_extrude(height = h, twist = -twist_deg, slices = slices, convexity = 10)
            knurl_profile_2d();
    }
}

module top_rounding_cutter() {
    // Cutter to round over the top outside corner of the knob
    difference() {
        translate([0, 0, total_height - top_fillet_radius])
            cylinder(r = radius + 2, h = top_fillet_radius + 1);

        translate([0, 0, total_height - top_fillet_radius])
            rotate_extrude($fn = 72)
                translate([radius - top_fillet_radius, 0, 0])
                    circle(r = top_fillet_radius, $fn = 36);

        cylinder(r = radius - top_fillet_radius, h = total_height + 2);
    }
}

module thumb_knob() {
    difference() {
        // Main body with knurling
        diamond_knurl_cylinder(total_height);

        // Top fillet cutter
        top_rounding_cutter();

        // Central through-hole for bolt
        translate([0, 0, -1])
            cylinder(d = bolt_diameter, h = total_height + 2, $fn = 48);

        // Hex pocket underneath
        translate([0, 0, -0.1])
            cylinder(r = hex_nut_radius, h = hex_nut_depth + 0.1, $fn = 6);
    }
}

// Render the knob
color(knob_color)
    thumb_knob();

// Optional preview of the M6 nut seated in the socket
if (nut_preview) {
    color(nut_color)
        translate([0, 0, 0.05])
            difference() {
                cylinder(r = hex_nut_radius - 0.1, h = hex_nut_depth - 0.1, $fn = 6);
                translate([0, 0, -0.5])
                    cylinder(d = 6, h = hex_nut_depth + 1, $fn = 36);
            }
}