Setting the part cooling fan and cooling correctly for each material

Highlighted terms are explained briefly when you hover over or tap them.

The part cooling fan blows directly onto the freshly printed material. It makes sure the material sets quickly so that overhangs, bridges and fine details hold. Too much cooling, however, weakens the adhesion between layers and promotes warping. The right setting therefore depends heavily on the material.

What cooling does

• More cooling: sharper details, better overhangs and bridges, less deformation on small parts.
• Less cooling: better layer adhesion, stronger parts, less stress and warping.

With PLA, the benefits of cooling almost always outweigh the drawbacks. With ABS, ASA, nylon and PC it is the other way round. PETG sits in between.

Fan values by material

The values below come from Bambu Lab’s material specifications, the OrcaSlicer base profiles and the Prusa Knowledge Base. They are starting values. Always check your filament manufacturer’s specifications too.

A few explanations:

• PETG: Prusa recommends printing the first layers without the fan and then at about half power. For maximum strength the fan can also stay off completely. Bambu Lab gives 0 to 80 % for PETG HF. More in Printing PETG.
• ABS and ASA: Bambu Lab gives 0 to 80 %. The upper end is intended for overhangs and bridges. The OrcaSlicer base profiles keep the fan at 10 % for layers of normal length and only increase it for very short layer times.
• TPU: Most filament manufacturers let the fan run. In the TPU 95A data sheet (PDF), Prusament gives 30 to 50 %, Bambu Lab gives 50 to 100 % for TPU 95A HF, and Polymaker simply says “on” for PolyFlex TPU95. Only the general guide to flexible materials in the Prusa Knowledge Base advises switching cooling off. If in doubt, try medium cooling and adjust according to the result. More in Printing TPU.
• PA and PC: Bambu Lab gives 0 to 60 % for both PA6-CF and PC. With these materials, warping is a bigger problem than a messy overhang.

The first layers

Almost all profiles switch the fan off for the first layer, and many for the first 2 to 3 layers. The warm material adheres better to the bed and the first layer does not warp. After that the fan ramps up to the set value. In some slicers you can set the layer at which full speed is reached, to make the transition smoother.

Adhesion problems therefore rarely have anything to do with the fan, as long as it is off in the first layers.

Minimum layer time

With small parts or narrow tips, a layer is finished in a few seconds. The next layer then lies on material that is still soft, and the part deforms. Two settings help against this:

• Ramp up the fan on short layers: If the layer time falls below a certain value, the fan spins faster. In OrcaSlicer, for example, this is called “Fan speed threshold”, with a layer time from which full speed applies.
• Print more slowly on short layers: If the layer time falls below a minimum value, the printer slows down until a minimum speed is reached. The OrcaSlicer base profiles use values between about 2 and 8 seconds, depending on the material.

A simple trick if the tip still gets soft: print two parts at the same time. Each layer then has twice as long to cool.

Overhangs and bridges

Most slicers let you set a separate fan speed for overhangs and bridges. It only applies while these areas are being printed.

• PLA: 100 %.
• PETG: 80 to 100 % for bridges, otherwise they sag.
• ABS, ASA: about 50 to 80 %.
• PA, PC: up to 60 %, less depending on the profile.

It also helps to print bridges and steep overhangs more slowly. More in Sagging bridges.

Auxiliary fans and chamber fans

Some printers have further fans in addition to the fan on the print head:

• Auxiliary fan (aux fan): a large fan at the side of the build volume that blows onto the part as well. It helps with PLA with very large overhangs or at high speed. With ABS, ASA, PA and PC it is better left off, because it cools the build volume.
• Chamber fan (exhaust): draws warm air out of the build volume. With PLA in enclosed printers this is important, otherwise it gets too warm and the material softens before it reaches the nozzle. Opening the lid or door a crack has a similar effect. With ABS and ASA the chamber fan stays off or only runs through a filter.

Typical failure patterns

Continue with: Print speed and Setting the print temperature.