3D Printed Resin Part: remove support nubs and prep for primer

3D Printed Resin Part sanding is easiest when you treat it like a repeatable workflow: remove the defects you can see, then refine the scratch pattern until primer or a topcoat can hide it. Below is a practical sequence to remove support nubs and prep for primer, without chasing new scratches at every step.

Why Sanding Matters

On 3d printed resin part, sanding isn’t just “making it smooth.” You’re controlling the scratch depth so the next layer (primer, paint, or clear) bonds evenly and looks consistent. Jumping grits too fast leaves deep marks that show up as ripples or dull spots after coating.

Tools

• Sanding block or small foam pad (keeps faces flat)
• Spray bottle with clean water (for wet sanding when safe)
• Soft brush or microfiber to clear dust
• Good lighting (raking light reveals ridges and nubs)
• Respirator and gloves (especially for resin/composite dust)

Grit Sequence

• 120 grit
• 180 grit
• 220 grit
• 320 grit

Step-by-Step

1. Knock down the worst highs first. Clip or scrape obvious support nubs/strings, then wipe the part clean so you’re not grinding debris into the surface.
2. Establish the baseline scratch pattern. Start with 120 Grit (25-Pack) using light, even pressure. Work in one direction, then switch 90° so you can see when the previous marks are gone.
3. Check your progress the right way. Dry the surface (or blow off dust) and inspect under raking light. Any shiny dots are still “high” and need more time at the current grit.
4. Refine, don’t re-shape. Move to 220 Grit (50-Pack) and focus on removing the previous grit’s scratches—no extra pressure. If you see a deep line that won’t fade, drop back one step and re-level.
5. Use wet sanding only when it helps. A few drops of water can reduce clogging and keep the scratch pattern more uniform. Keep it minimal and dry the part often so you don’t miss low spots.
6. Finish for primer/paint. Use 320 Grit (100-Pack) to create a consistent, fine scratch pattern that primer can fill. Stop when the whole face looks uniform under the same light and angle.

Special Cases

If you’re sanding resin, fiberglass, or carbon fiber, prioritize dust control: wet sanding (when safe) plus a respirator reduces airborne particles. For sharp edges, wrap the sheet around a soft pad so you don’t burn through corners.

Pro Tips

• Change sheets when cutting slows—pushing harder creates random deep scratches.
• Mark the surface lightly with a pencil: remaining lines show where you still need to sand.
• Clean between grits to avoid cross-contamination (one rogue coarse grain can re-scratch everything).
• Keep strokes long and consistent on flat faces; use short, controlled strokes on curves.

Aftercare

• Rinse or wipe the part thoroughly, then let it dry completely before priming.
• Use a tack cloth or microfiber to remove fine dust from pores and seams.
• Store sheets flat and dry so edges don’t curl or crease.

FAQs

• Can I skip grits? You can, but only if the scratch pattern from the previous grit is already shallow. If you still see deep lines, don’t jump.
• Wet or dry? Dry is faster for early shaping; wet can help with clogging and consistency on finer stages—just keep moisture controlled.
• How do I know I can move up? When the entire surface shows only the current grit’s scratch pattern under raking light.

Watch & Learn

Tip: watch for the moment the scratch pattern becomes uniform. That’s your cue to move up a grit—moving early is the fastest way to create “mystery scratches” that show up after primer.

Need to restock for this workflow? Start with 120 Grit (25-Pack), refine with 220 Grit (50-Pack), and finish with 320 Grit (100-Pack) so every step removes the previous scratches instead of creating new ones.