Answer
Refine metal through 180, 220, 320, then 400 or 600. Clean before every grit change.
Why it happens
The metal was not refined through enough intermediate grits.
Recommended grit
Use 180, 220, 320, then 400 or 600 for finer prep.
Wet or dry
Dry for shaping; wet for 400 grit and finer finishing stages.
Success check
The old scratch direction is no longer visible.
What to do
- Remove residue from the metal.
- Sand with the next finer grit until the old pattern is uniform.
- Change sanding direction slightly between grits to see progress.
- Clean before each grit change.
Avoid: Do not leave loose grit or debris on the surface.