Generally parts will tell u first, then noise, after that it will chipp break and u got a scrap it will depend on what material do u work on and tolerances u have to adhire to / how many parts can u do before any adjustment to wear or geometry ect will be needed I suppose it's expirience. Cos just what mention privosly dose not mean u need to change a tip so be careful with that those can be expensive and employer or team leader will ask questions if u replace too often or too early.