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Slide 002: Common Print Defects — Identification and Root Causes

Slide Visual

Common Print Defects — Identification and Root Causes

Slide Overview

This slide serves as a visual defect identification guide. Students learn to recognize the most common FDM print failures by appearance, understand their root causes, and apply systematic troubleshooting logic. Being able to quickly identify a defect is the first step toward resolving it.

Instruction Notes

Defect Identification Guide

1. Stringing / Oozing - Appearance: Thin hair-like filament threads between separate features - Root cause: Molten plastic leaks from the nozzle during travel moves - Key factors: Retraction distance too short, nozzle temperature too high, travel speed too low - Fix: Increase retraction (direct drive: 0.5-2mm, Bowden: 3-6mm), decrease nozzle temp by 5-10°C, enable combing/avoid crossing perimeters

2. Warping / Corner Lift - Appearance: Corners or edges lift off the build plate, part curves upward - Root cause: Thermal contraction — upper cooling layers pull corners up - Key factors: Insufficient bed temperature, no enclosure (ABS/Nylon), draft exposure, no brim - Fix: Increase bed temp, add brim (5-8mm), use enclosure for high-temp materials, eliminate drafts

3. Layer Shifting - Appearance: All layers above a certain height are offset horizontally - Root cause: Stepper motor lost steps due to physical collision, loose belt, or electrical issue - Key factors: Belt tension, stepper current, print head collision with curled features - Fix: Tighten belts, check stepper drivers, reduce print speed and acceleration

4. Under-Extrusion - Appearance: Thin walls, gaps in infill, weak layer bonding - Root cause: Less filament deposited than expected - Key factors: Partial clog, extruder gear grinding, incorrect filament diameter setting (1.75 vs. 2.85mm), low flow rate - Fix: Clean/replace nozzle, check extruder tension, verify slicer filament diameter, calibrate e-steps

5. Over-Extrusion - Appearance: Blobby surfaces, rough texture, dimensional inaccuracy (parts too large) - Root cause: Too much filament deposited - Key factors: Flow rate too high, filament diameter slightly larger than setting, e-steps over-calibrated - Fix: Reduce flow rate by 2-5%, measure actual filament diameter with calipers, recalibrate e-steps

6. Pillowing - Appearance: Bumpy, rough top surface with small holes showing infill beneath - Root cause: Insufficient top layers to bridge over infill gaps - Fix: Increase top layers to 5-6 (at 0.20mm) or increase infill density above 20%

7. Elephant's Foot - Appearance: First few layers bulge outward, base is wider than designed - Root cause: First layer too hot and compressed, weight of upper layers deforms soft base - Fix: Reduce bed temperature by 5°C, increase Z-offset slightly, use elephant's foot compensation in slicer (0.1-0.2mm)

8. Delamination / Layer Separation - Appearance: Visible cracks between layers, layers peel apart - Root cause: Insufficient inter-layer bonding due to low nozzle temperature or excessive cooling - Fix: Increase nozzle temp by 5-10°C, reduce fan speed for materials like ABS/PETG, check for drafts

Key Talking Points

  1. Every print defect has a root cause — learn to read the symptoms like a diagnostic technician
  2. Most defects fall into thermal issues (temperature), mechanical issues (motion), or extrusion issues (material flow)
  3. Always change only ONE variable at a time when troubleshooting, then reprint to isolate the cause

Learning Objectives (Concept Check)

  • [ ] Students can visually identify the 8 most common FDM print defects
  • [ ] Students can explain the root cause of each defect
  • [ ] Students can propose at least one corrective action for each defect type

Last Updated: 2026-03-19