I designed a part using CAD software to combine it with a mechanical component which already has holes on it. The locations are correct as I have the CAD file for that component from the manufacturer.
I 3D printed the part and added threaded inserts. When I tightened the screws to put the 3D printed part and the mechanical component together, often I had difficulty in tightening 1-3 out of about 10 screws. When I removed the two parts, sometimes there were scratches or lost paints around the holes of the mechanical part. What are the causes and how to make it easy to tighten all screws?