Think in stages, not numbers
Coarser grits level layer ridges. Medium grits remove coarse scratches. Fine grits prepare for paint, polish, or clear coat. If you skip the middle stage, the final finish often shows scratches even if the part feels smooth.
When to start coarse
If layer lines are visibly raised, start with a grit that can flatten them. Use controlled pressure and keep checking the shape. Coarse sanding is useful, but it is also where most detail loss happens.
When to move up
Move to the next grit only when the previous scratch pattern is consistent. Do not move up because the surface feels smoother for ten seconds. Look under side light. If old lines remain, keep working at the current stage.
Dry vs wet sanding
Dry sanding is faster for early shaping. Wet sanding helps control dust and heat during later refinement. On PLA, heat control matters because the plastic can smear if you push too hard for too long.
Edges need a different touch
Flat faces can take a block. Corners and details need a lighter pass. The goal is to keep intentional geometry crisp while removing the print texture that makes the part look unfinished.
Quick grit logic
- Use lower grit to level visible ridges.
- Use middle grit to erase the first scratch pattern.
- Use fine grit to prepare for the final surface treatment.
Bottom line
The best sanding grit sequence is controlled, patient, and matched to the defect. A clean final surface comes from moving up at the right time, not from rushing to the finest paper.