I have a very good set of HSS drills to 1.25" by 64ths and also a good assortment of annular cutters. So for me it will be a combination of those along with some boring on the mill where needed. Not a fast process for sure. I have my sizes now and layout so if my wife has no large plan today I may just get started.For the larger diameter holes (1" / 25mm+): what sort of cutters are y'all using to machine the initial hole? Annular cutter? HSS or Carbide? Recommended brands? Or just start with a 1" drill and then lots of time with a boring head?
Water jet / plasma / laser is cheating.
I've used a bi-metal hole saw on 1" thick thick steel a couple of times...that was painful. And that was with a clearance hole for chip evac.