What is the min. voltage cordless drill should I use to drill a hole in a 2 cm thick stainless steel
When drilling stainless go slow (do not over heat the metal) If the metal gets hot it will "work harden" and is hard to drill with a drill press. It may take a while but can be done with a good quality 1/2 drill motor and good drill bits. If you are purchasing a drill get one with at least 2 speeds and a 3 speed would be best used on the lowest speed. Cutting fluid or a light oil will help reduce heat and improve the cutting. Last you will want a high quality drill bit something with a titanium nitrite coating or carbide. I have a full set of carbide cutters for stainless but these are very expensive and if you drop them on cement they can shatter. If you only have 1 battery stop when the motor starts bogging down and recharge the battery. I have drilled 1-3/8" holes through stainless with my Dewalt but it did take 2 5AH batteries and part of a 4AH battery the stainless was only 3/4" thick.