[danner]

I cut the opening smaller than the TFT display and slowly opened it up. I did it by eye, so it's not perfectly straight, but after I did it I thought of possibly a better way. You could c-clamp a metal straight-edge to the panel and parallel to the cutout you want to file. The metal straight-edge will act as a stop gauge preventing you from removing too much material. You might have to use two c-clamps in case they slip and the panel moves.