You can also buy tube notchers such as this
http://https://m.vevor.co.uk/tube-pipe-notcher-c_10115/vevor-pipe-tubing-notcher-pipe-and-tube-notcher-hole-saw-0-60-degree-2-capacity-p_010631772408?gclid=CjwKCAjw7p6aBhBiEiwA83fGuiDMk F8FGedZ12lo0jUXY4xVw11FnOyAY8gogK9e_ufDGr6Yn0zCtho CpYcQAvD_BwE