🎯 Lesson: Sanding and Surface Finishing

🧠 Focus: Learn how to improve the visual and tactile quality of your 3D prints through sanding, smoothing, and finishing techniques.

✅ Lesson Summary

3D prints—especially FDM—often show visible layer lines or surface imperfections. This lesson teaches students how to sand, smooth, and prepare prints for painting or display. From basic grit selection to advanced chemical smoothing, this module covers everything needed to enhance both the look and feel of your prints.

🎓 Learning Objectives

By the end of this lesson, students will be able to:

• Choose the right sanding tools and grits

• Smooth rough surfaces and remove support marks

• Apply chemical smoothing (optional) for materials like ABS

• Prepare prints for painting or aesthetic display

• Understand safety precautions for sanding and finishing materials

📘 Lesson Content

🟩 1. Why Sand Your Prints?

Sanding improves:

• Aesthetic appeal (removes visible layer lines)

• Tactile quality (smoother to touch)

• Paint adhesion (smoother base coat)

• Professional appearance for prototypes or client-ready parts

🧠 Sanding is most common with FDM prints due to their layer-by-layer structure. Resin prints may only require minor touch-ups.

🟨 2. Choosing the Right Sandpaper

🛠️ Use wet sanding (water + high-grit paper) for a cleaner surface and less airborne plastic dust.

🟥 3. Tools for Sanding

• Sandpaper sheets or sanding sticks

• Needle files for detailed areas

• Hobby knives for scraping stringing or burrs

• Rotary tools (e.g., Dremel) with sanding drums (optional)

• Flexible sanding sponges (good for curves)

⚠️ Wear a mask and safety glasses when dry sanding. PLA dust is non-toxic but irritating if inhaled.

🟦 4. Sanding Workflow (FDM)

Step-by-step:

1. Start with coarse grit (100–150) to remove high ridges or support scars

2. Move to medium grit (220–400) for smoothing outer surfaces

3. Finish with fine grit (600–1000+) for polishing or paint-ready finish

4. Clean with a damp cloth between grits to remove plastic dust

5. Use filler primer before painting for best finish

🧠 Pro Tip: Sand in a circular motion to blend layer lines more evenly.

🟧 5. Sanding Resin Prints

• Most resin prints need minimal sanding due to high surface quality

• Use 400–600 grit sandpaper on support nubs or seams

• Wet sand only after the model is fully cured and rinsed

• Avoid over-sanding details (resin is brittle and can chip)

🟪 6. Chemical Smoothing (Advanced)

Works best with ABS and ASA prints (not PLA or PETG).

Acetone vapor smoothing:

1. Place the print in a sealed container

2. Add a small dish of acetone (not touching the print)

3. Leave for 5–15 minutes until the surface smooths

4. Remove and let the print air out

⚠️ Do this only in a well-ventilated space or outdoors. Acetone is flammable and hazardous.

Alternative: Use smoothing agents like XTC-3D epoxy coating for any material.

🟫 7. Post-Sanding Finishing Options

🧠 Summary

Sanding is an essential skill in taking 3D prints from “functional” to “finished.” Whether you’re preparing a part for display, painting, or client presentation, effective sanding and surface finishing can dramatically enhance the final product.

Final Checklist:

✅ Choose the right grit sequence
✅ Use wet sanding to reduce mess
✅ Don’t rush the lower grits—foundation matters
✅ Always clean before applying paint or primer
✅ Safety first: mask, gloves, ventilation

📂 Optional Activities

Assignment:

1. Print a simple model with visible layer lines

2. Document the sanding process in 3 stages:

   • Before sanding

   • After medium grit

   • After fine grit or finishing

3. Optional: Apply primer and paint, and share results

📎 Additional Resources

• How to Sand 3D Prints – MakerBot

• Smooth Prints with Acetone Vapor – All3DP

• Finishing FDM Prints with Filler Primer (YouTube)