A quick demonstration of the basic notching operation on a Horizontal Milling Machine.
Step 1: Cutting Notch with Ordinary Hole Saw -
Center tubing to be notched on appropriate jig/holder.
Bringheli jig being used here setup in a simple mill vise.
Centered the tubing using and edge finder then moving table to the center ((edge finder / 2) + tube diameter/ 2)