ABS and ASA: cracks between layers, parts that warp and a strong smell (enclosure and ventilation)

Symptom

With ABS or ASA, horizontal cracks appear between layers, especially on tall parts; the base curls or comes loose; and the printer gives off a strong plastic smell while printing.

Likely causes, from most to least likely

1. Shrinkage on cooling: if the part cools quickly (open printer, draughts, cold room), the stress exceeds the layer bond and it cracks or warps.
2. Too much part cooling fan or a cold chamber.
3. Plastic not melting properly due to a cold nozzle or high speed, or a partly clogged nozzle, weakening the layer bond.
4. Very dense infill or many walls: Bambu Lab advises not exceeding 50% infill or 6 walls to reduce shrinkage.
5. An unprepared plate: ABS and ASA need a heated bed and glue on PEI.
6. Smell: when printed, ABS and ASA release gases such as styrene, which may be harmful to health.

Checks to tell which one it is

• Are you printing with the printer closed or with an enclosure? Without one, large parts almost always warp or crack.
• Look for draughts nearby (windows, air conditioning) and check the room temperature.
• Check the part cooling fan and the nozzle and bed temperatures in the profile.
• Check whether the room is ventilated and whether anyone sensitive is nearby.

Before you start

Before taking anything apart, cleaning or adjusting it, switch the printer off and unplug it, unless a step says otherwise, and do not touch the nozzle, the heater block or the bed until they have cooled down. If in any doubt about electricity, heat or moving parts, stop and ask a professional.

Step-by-step fix

1. Starting temperatures

   Use the filament maker's profile. As a reference, Prusa gives ABS 255 °C nozzle with the bed at 100 °C (80-110 °C depending on part size), and ASA 260 °C with the bed at 105 °C for the first layer and 110 °C for the rest.

   Check: Layers fuse well with no gaps.

   If that does not fix it: Warm the chamber and remove draughts (next step).

2. Warm chamber and no draughts

   Print with the printer closed or in an enclosure, away from draughts. Without an enclosure, enable a draft shield in the slicer. If your printer does not control chamber temperature, raising the bed warms it indirectly: for its X1C and P1S, Bambu Lab suggests preheating the bed to its maximum for about 15 minutes before starting when the room is cold.

   Check: The base does not lift and no cracks appear.

   If that does not fix it: Reduce the fan (next step).

3. If it cracks: less fan, more heat

   Lower the part cooling fan's maximum speed, raise the bed by 5-10 °C (and the chamber by 5 °C if adjustable) and, if needed, raise the nozzle slightly or reduce speed. Keep the door and lid closed.

   Check: Tall parts come out without cracks.

   If that does not fix it: Check adhesion (next step).

4. Plate adhesion

   Clean the plate, apply glue stick and add a brim. Do not put acetone or dissolved ABS or ASA on powder-coated plates.

   Check: The part stays stuck until the end.

   If that does not fix it: Dry it: ABS and ASA absorb moisture (prevention).

5. Ventilation and safety

   Print in a well-ventilated room but without draughts on the part, or with air filtration or extraction, and avoid long prints in bedrooms or living rooms. For long jobs, Bambu Lab advises a vapour-filtering (activated carbon) mask; if children, pregnant women or people with asthma are present, ventilate more or do not print these materials. Replace your printer's carbon filter when due.

   Check: No smell builds up in the room.

   If that does not fix it: Consider another material for that part or print it elsewhere.

6. Look after the printer

   With a lot of heat inside the enclosure, Prusa warns the fan shroud and other plastic printer parts can deform. Fumes also settle on the glass and other parts: clean them every now and then.

   Check: The printer's parts stay in good condition.

   If that does not fix it: Replace deformed parts with ones made of a more heat-resistant material.

Prevention

• Print ABS and ASA enclosed and away from draughts.
• Dry the spool if it has been left out, at the maker's temperature (for example, Prusa: ASA at 80 °C for 4 h).
• Ventilate the room without draughts on the part and do not print these materials near children or people with breathing problems.

Still not fixed?

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Printers it applies to

Any FDM (filament) 3D printer, from any brand.

Materials: ABS and ASA.

Official sources

This guide summarises the official documentation linked here:

• ABS (material guide) · Prusa Research
• ASA (material guide) · Prusa Research
• ABS / ASA / PC Usage Guide · Bambu Lab
• Model interlayer cracking · Bambu Lab
• Guide to FDM Printing Filament (odour and enclosure) · Elegoo
• Drying filament (drying temperatures) · Prusa Research