knob_radius = 24;

knob();

module knob() {
	union() {
		difference() {
			sphere(r=knob_radius);
			translate([0, 0, 0-(knob_radius)]) {
				cylinder(r1=knob_radius, r2=knob_radius, h=knob_radius);
			}
			shaft_hole();
		}
		indentations();
	}
}

shaft_radius = 6.4; // ~ .25"
shaft_height = 13;
shaft_smoothness = 20;
flat_size = 5;

module shaft_hole() {
	difference() {
		translate([0, 0, -1])
		cylinder(r=shaft_radius, h=shaft_height, $fn=shaft_smoothness);
		rotate( [0,0,90])
		translate([-7.5, -7.5, 0])
		cube(size=[flat_size, 15, 13], center=false);
	}
}

knurls = 16;
knurl_size = 10;
layers = 18;

module indentations() {
	for (layer = [0:layers]) {
		for (z = [0:knurls])  {
			rotate([
				0,
				-1 * (150/layers)*layer + 40,
				90+((360/knurls)*z)
			])
			translate([knob_radius - (knurl_size/3), 0, 0])
			rotate([(120/layers)*layer, 0, 0])
			scale(1- (layer/layers))
			cube(size=knurl_size);
		}
	}
}