what percent of damage should i wait to repair a weapon for best result. Also is there repair formula somewhere?
Your chances of successful repair are not altered by weapon deterioration %, but rather how many times it has been broken/repaired.
What tool? The one you can craft or the one that Rondo sells you for 2000 caps?
Rondo is the guy who teaches armorcrafting 1-2. At the NCR's workbench. He also sells supertool.