/* [Knob Dimensions] */
outer_diameter = 30.0;       // [15:1:60]
knob_height = 14.0;          // [8:1:40]
top_fillet_radius = 2.0;     // [0.5:0.5:5]

/* [Knurling Details] */
knurl_ridges = 42;           // [20:2:80]
knurl_depth = 0.75;          // [0.3:0.05:2.0]
helix_turns = 0.35;          // [0.1:0.05:1.0]

/* [Hardware Pockets] */
through_hole_diameter = 6.5; // [3:0.1:12]
hex_nut_af = 10.0;           // [5:0.1:20]
hex_nut_depth = 5.0;         // [2:0.5:15]

/* [Appearance] */
knob_color = "Charcoal";     // [Charcoal, DarkSlateGray, SteelBlue, FireBrick, DarkGreen, OrangeRed]

/* [Quality] */
$fn = 96;

// Derived values
r_outer = outer_diameter / 2;
r_inner = r_outer - knurl_depth;
hex_radius = (hex_nut_af / 2) / cos(30); // Across-flats to across-corners radius
twist_degrees = helix_turns * 360;

module diamond_knurled_body(h, r_out, depth, ridges, twist_deg) {
    slices_count = max(30, ceil(h * 3));
    
    // Smooth transition bevel profile for top edge
    difference() {
        // Knurled textured cylinder
        intersection() {
            // Clockwise twisted teeth
            linear_extrude(height = h, twist = twist_deg, slices = slices_count, convexity = 10)
                knurl_2d_profile(r_out, depth, ridges);
            
            // Counter-clockwise twisted teeth
            linear_extrude(height = h, twist = -twist_deg, slices = slices_count, convexity = 10)
                knurl_2d_profile(r_out, depth, ridges);
        }
        
        // Filleted/rounded top edge cutter
        if (top_fillet_radius > 0) {
            translate([0, 0, h - top_fillet_radius])
            difference() {
                cylinder(r = r_out + 1, h = top_fillet_radius + 0.1);
                
                // Torus-like inner solid
                cylinder(r = r_out - top_fillet_radius, h = top_fillet_radius + 0.1);
                
                rotate_extrude(convexity = 4)
                translate([r_out - top_fillet_radius, 0, 0])
                circle(r = top_fillet_radius, $fn = 48);
            }
        }
        
        // Chamfer on bottom edge to ensure smooth feel and easy print release
        translate([0, 0, -0.01])
        difference() {
            cylinder(r = r_out + 1, h = 0.8);
            cylinder(r1 = r_out - 0.8, r2 = r_out, h = 0.8);
        }
    }
}

module knurl_2d_profile(r_out, depth, ridges) {
    r_in = r_out - depth;
    points = [
        for (i = [0 : ridges * 2 - 1])
            let(angle = i * 360 / (ridges * 2),
                r = (i % 2 == 0) ? r_out : r_in)
            [r * cos(angle), r * sin(angle)]
    ];
    polygon(points);
}

module thumb_knob() {
    difference() {
        // Main knurled body
        diamond_knurled_body(
            h = knob_height,
            r_out = r_outer,
            depth = knurl_depth,
            ridges = knurl_ridges,
            twist_deg = twist_degrees
        );
        
        // Through hole
        translate([0, 0, -1])
            cylinder(d = through_hole_diameter, h = knob_height + 2, $fn = 64);
            
        // Hex nut pocket underneath
        translate([0, 0, -0.01])
            cylinder(r = hex_radius, h = hex_nut_depth, $fn = 6);
            
        // Slight entry chamfer for hex nut
        translate([0, 0, -0.01])
            cylinder(r1 = hex_radius + 0.5, r2 = hex_radius, h = 0.5, $fn = 6);
            
        // Top slight countersink/relief for clean look
        translate([0, 0, knob_height - 0.5])
            cylinder(d1 = through_hole_diameter, d2 = through_hole_diameter + 1.0, h = 0.51, $fn = 48);
    }
}

color(knob_color)
    thumb_knob();