I’m getting polishing lines in my job

Polish lines are just part of the job. Unfortunately you get them. You can minimise them by cutting thoroughly with Menzerna 439T and making sure you cut all the sanding marks out, then do a clean run over your work by cleaning the cutting wheel on the rake. Another way to minimise lines, is to use a variable speed polisher to do a 2nd cut after using the 9 inch grinder for the initial cut.