Quick answer
ABS cracks and splits between layers because the plastic shrinks as it cools, and uneven cooling pulls finished layers apart. The fix is to keep the whole print warm and let it cool slowly: run the printer inside an enclosure (aim for 40-55 C inside), keep the hotend hot enough for a strong bond (around 240-250 C), turn the part cooling fan down to 0-20%, and keep the machine out of cold drafts.
Why ABS cracks and separates between layers
ABS has a high thermal contraction rate, so it shrinks noticeably as it cools from print temperature back down to room temperature. While the lower layers are cooling and contracting, fresh hot layers are still being added on top. That temperature mismatch builds internal stress in the part. When the stress grows larger than the bond holding two layers together, the print lets go - usually as a horizontal crack partway up a wall, or as corners that lift and delaminate. Tall parts, thin walls, a cold or drafty room, and an aggressive cooling fan all make the problem worse.
1. Put the printer in an enclosure
An enclosure is the single most effective fix. It traps the printer’s own heat and keeps the whole object warm for the entire print, so the bottom and top layers stay at a similar temperature and shrink together instead of tearing apart. Aim for roughly 40-55 C inside the enclosure. Even a simple cardboard or acrylic box over an open-frame machine makes a large difference on ABS.
2. Eliminate cold drafts
ABS hates sudden temperature changes. An open window, an air-conditioning vent, or even a doorway that gets opened mid-print can chill one side of the model and trigger a split. Move the printer away from drafts and exterior doors, and avoid printing ABS in a cold room. If you can, run longer ABS prints when the room temperature is stable.
3. Turn the part cooling fan down
ABS does not need much part cooling, and a fan blowing across the layers prevents them from properly welding together. Set the part cooling fan to 0-20% for most ABS parts - off is fine for solid geometry, with just a little fan reserved for small overhangs and bridges. Too much fan is one of the most common causes of mid-print cracking.
4. Print hot enough for a strong bond
If the nozzle is too cool, the new layer never fully fuses to the one below it. For ABS, a nozzle temperature in the 240-250 C range generally gives the best layer adhesion; start around 240 C and raise it in 5 C steps if you still see splitting. Make sure your filament is dry, as damp ABS also bonds poorly.
5. Keep the bed hot
A hot bed holds the base of the print in place and reduces the early warping that later grows into cracks. Set the bed to roughly 95-110 C for ABS. A clean bed and a light coat of adhesive (glue stick or ABS slurry) help the first layers stay locked down while the rest of the part builds.
6. Add walls and slow down
Thin walls have little material to resist shrinkage stress, so they crack first. Use at least 2-3 perimeters (walls) for functional ABS parts, and bump up infill on load-bearing pieces. Slowing the print speed also gives each layer more time to bond to the one beneath it, which improves adhesion on tall or large models.
7. Let the print cool slowly
Do not yank the finished part off a hot bed into a cold room. Leave the enclosure closed and let everything cool gradually after the print completes. A slow, even cool-down lets the internal stresses relax instead of snapping a layer line at the last moment.
Frequently asked questions
Do I need a heated chamber to print ABS?
Not strictly - a passive enclosure that traps the printer’s own heat and holds around 40-55 C is enough for most ABS parts. A powered heated chamber mainly helps with very large or tall models.
Why does my Bambu Lab A1 crack ABS?
The A1 and A1 Mini are open-frame printers with no enclosure, so ABS cools too fast and splits on all but the smallest parts. Add a simple enclosure, or use an enclosed printer like the X1 or P1 series for reliable ABS.
What nozzle temperature stops ABS delamination?
Printing around 240-250 C usually gives ABS enough heat to weld layers together. If prints still separate, raise the nozzle in small steps and confirm your filament is dry.
Is ASA the same as ABS for cracking?
ASA behaves very similarly and benefits from the same fixes - enclosure, low fan, hot nozzle and bed, and no drafts. ASA is more UV-resistant but shrinks and cracks in the same way if it cools unevenly.