The part breaks between layers
An FDM part is always weaker in the Z axis. With the right settings, that difference can be kept to 20-30%; with poor settings, up to 70%.
What the failure looks like
The part separates cleanly along a horizontal line, as if it were glued sheets. It breaks with little force and always in the direction of the layers.
Causes, most likely first
- 01
Temperature too low
Lower temperature = less fusion between layers. It is the most important factor.
- 02
Fan speed too high
Cools the layer before the next one can melt onto it.
- 03
Excessive layer height
0,3 mm layers with a 0,4 nozzle reduce the contact surface area.
- 04
Wrong orientation
The stress falls right in the direction of the layers.
- 05
Damp filament
Steam bubbles create micro-gaps at the joint.
Step-by-step fix
1. Increase by 10 °C
PLA at 215-220 °C, PETG at 245 °C. Check that excessive stringing does not appear.
2. Lower the fan speed
Technical PLA 40-60% instead of 100%. PETG 30%. ABS 0%.
3. Reduce the layer height
Going from 0,3 to 0,2 mm significantly improves the bond.
4. Reorient the part
Position the part so that the main force goes across the layers, rather than pulling them apart. For a hook, the hook should be printed lying down.
5. Increase the number of perimeters
3-4 perimeters provide more strength than increasing infill from 20 to 40%.
6. Switch material if needed
PETG and ABS are considerably tougher than PLA for functional parts.
| Setting | Good finish | Strong part |
|---|---|---|
| Temperature | Low end of range | High end of range |
| Fan speed | 100% | 0-40% |
| Layer height | 0,12-0,16 mm | 0,2 mm |
| Perimeters | 2 | 4 |
| Infill | 10-15% | 30-40% gyroid or cubic |
So it doesn't happen again
- Keep two profiles: 'aesthetic' and 'functional'. Don't try to make one do both jobs.
- Consider orientation when designing, not when slicing.
Related questions
Does increasing infill to 100% make the strongest part?
It's rarely worth it: going from 40% to 100% adds a lot of time and weight for very little gain. Increase perimeters first.
Keep reading
Want to go deeper? We have a full article about this on the blog.
What if it isn't worth your time?
Sometimes the part is more urgent than the learning curve. We're a workshop in Viladecavalls: send us the file and we'll print it with the right material and settings.
Still not working?
Tell Marco which printer and material you use and he'll tell you what to change.
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