i am CNC machines repairman. Mostly mechanical and electrical parts and units. I am wondering how cnc retrofiting is done. Specifically i am interested in how operating system (for example SINUMERIK) is adaptable to machine which is modernized. How to program PLC? Which programming language do i have to know (C, LADER...). I was trying to find somethig on internet but i cant find enithing. Maybe someone have manuals or something, or could share his experience with me how to do this kind of projects.