Warping: How to Prevent Lifting Corners in 3D Printing

The first half hour of the print goes fine, then the corners slowly begin to lift off the bed. The cause is plastic shrinking as it cools: as the upper layers cool, they pull the layers below inward, and stress concentrates most at the corners. ABS, ASA and nylon are the materials most prone to it, but it also appears with PLA on large, flat parts.

Symptoms

• The bottom corners of the part separate from the bed and curl upward.
• The ends of long parts lift and the underside bends like a "banana".
• In severe cases the part comes completely off the bed.
• On tall parts, cracks can also appear in the lower layers. See Layer separation.

What causes it?

Plastic expands when heated and shrinks when cooled. A newly printed layer is expanded while hot, and as it cools it also pulls the layer below along with it. The bigger and more angular the part, the more the material shrinks and the colder the environment, the stronger this pull. When the adhesion to the bed cannot withstand the force, the corner lifts.

1. Strengthen first layer adhesion

The first defense against warping is a good first layer. If bed leveling, Z offset and a clean bed surface are not right, other measures fall short. First check the steps in the First layer not sticking guide.

2. Set the bed temperature correctly

A hot bed keeps the lower layers at a temperature that reduces shrinkage. Approximate values:

With PLA, keeping the bed too high sometimes backfires: the lower layers soften and you get elephant's foot.

3. Add a brim

A brim is a wide single-layer border added around the part and joined to the part's first layer. It increases the contact area and spreads the pulling force at the corners. See Brim vs skirt vs raft.

• For PLA and PETG, a 5–8 mm brim is enough in most cases.
• For ABS and ASA, a 8–15 mm brim is recommended.
• The brim is removed after the print by hand or with a hobby knife.

Instead of a brim, adding small discs (mouse ears) only at the corners makes cleanup easier.

4. Keep the environment warm and steady

A sudden draft, an open window or an air conditioner cools one side of the print quickly and increases warping.

• Put the printer in a place away from drafts.
• Use an enclosure for ABS, ASA and nylon. An enclosure warms the air inside so the layers cool more slowly and evenly. See the ABS printing guide.
• If you have no enclosure, even a simple cardboard box or printer tent makes a difference. But make sure the control board and power supply stay outside it so they do not overheat.

5. Set the part cooling fan

Too much cooling makes the layers shrink quickly and unevenly.

• PLA: Fan off for the first 2–3 layers, then 100% can be used.
• PETG: Around 30–50%.
• ABS/ASA: Off or very low (0–20%), raised only on bridges and overhangs.

6. Adjust the design for warping

Sometimes the most effective fix is in the part itself:

• Round off sharp corners. Stress concentrates less at curved corners.
• If you can, split very large flat parts in two.
• Orient the part with a smaller footprint on the bed.
• Do not keep infill needlessly high. Dense infill increases shrinkage force. See Infill settings.

7. Adhesion helpers

• On a glass bed, a thin coat of glue stick or a bed adhesive made for the purpose.
• On a PEI surface, a clean, grease-free surface is enough for most materials.
• For ABS some people use a mixture of ABS dissolved in acetone ("ABS slurry"). Acetone is flammable and its fumes are irritating, so use it in a ventilated space and with care.

Frequently asked questions

Does PLA warp too?

Yes, especially on large, flat, angular parts or in a cold room. A brim, a clean bed and a position away from drafts are usually enough.

Can I fix a part that has already warped?

You can partly fix slight curves by softening the part with hot water or a heat gun and pressing it onto a flat surface. But for parts that need dimensional accuracy, the safest way is to print it again.

Can ABS be printed without an enclosure?

Small parts can be printed, but on larger parts warping and layer cracking are almost unavoidable. If you do not use an enclosure, think of alternatives such as ASA or PETG.