Why PETG cooling needs a lighter touch
PETG does not behave like PLA. Too much part cooling can make it brittle, reduce layer adhesion, and leave corners looking chalky instead of clear or glossy. Too little cooling can cause soft overhangs, droop on bridges, and messy edges, especially on warm days in Cape Town or in a workshop with poor airflow.
The goal is not maximum fan speed. It is controlled cooling that holds the shape of each layer without robbing the print of strength. For most parts, a moderate fan setting works better than full blast. If you are making covers, brackets, signage parts, or prototypes that must survive daily handling, keep cooling conservative and test in small steps.
- Start with low fan speed for the first layers.
- Increase cooling only when overhangs or bridges need support.
- Watch for brittle corners, which often means too much fan.
- Keep the room temperature stable where possible.
A simple fan starting point for PETG
A safe starting point is 0% to 20% fan for the first layers, then 20% to 40% for most of the print. For small detailed parts, you may need a bit more. For large functional parts, keep the fan lower so the layers fuse properly. If your machine uses automatic fan control, check what it is doing instead of leaving it to guess.
Use these settings as a guide, then adjust for your own printer, nozzle size, and filament brand. A 0.4 mm nozzle on a benchtop machine often behaves differently from a larger nozzle on a production unit. If you are printing in Epping during summer and the workshop runs warm, the same fan setting may cool less effectively than in a cooler room.
- First 2 to 5 layers: fan off or very low.
- Standard walls and infill: light to moderate cooling.
- Bridges: increase fan for a short section only.
- Top layers: a small fan boost can help surface finish.
When to increase fan speed and when not to
Increase cooling when you see drooping on bridges, rounded overhangs, or soft detail on small features. This can help with logos, vents, thin ribs, and parts with short unsupported spans. If the print starts to look stringy or the corners smear, the fan may be too low, or your nozzle temperature may be a bit high.
Do not turn the fan up just because the print looks glossy. Gloss is not a fault on its own. In fact, many PETG users prefer a slight sheen because it shows that the material stayed hot enough to bond well. If you are printing parts for a humid coastal environment, a clean bond matters more than a perfectly matte finish.
- Use more fan for bridges and small overhangs.
- Use less fan for load-bearing walls and thicker sections.
- Drop fan speed if corners lift or layers separate.
- Check nozzle temperature before chasing fan changes.
Cooling problems that look like temperature problems
Some print faults are easy to blame on fan speed, but the real issue may be temperature, speed, or poor first-layer setup. If the part is curling, the nozzle may be too close to the bed or the first layer may be overcooled. If layers split under light hand pressure, the fan may be too strong or the extrusion temperature too low.
Stringing can also mislead you. PETG often strings a little more than harder plastics, so do not over-correct with aggressive fan settings. Retract, dry the filament, and check travel moves first. In many cases, one small change fixes the fault better than a big fan jump. A careful test cube saves time and material, and a few Rand too.
- If layers split, reduce fan before raising temperature too much.
- If edges curl, check bed adhesion and first-layer heat.
- If stringing is heavy, dry the filament and adjust retraction.
- If fine details blur, increase cooling in small steps only.
How workshop conditions in South Africa change the result
Local conditions matter. In summer, a hot workshop can make PETG stay soft for longer, so parts may need a touch more cooling on small features. In winter or in a draughty space, too much fan can cool the print unevenly. Load-shedding can also interrupt a job and change the chamber temperature fast, so it helps to restart with the same settings and inspect the first layers carefully.
Dust and humidity are also part of daily printing. Keep filament sealed when not in use, especially in coastal areas. Moist PETG can pop in the nozzle and leave rough surfaces that look like cooling faults. If your print room is near a roller door or open loading bay, shield the machine from direct wind because even a light draught can affect bridging and corners.
- Keep filament dry and stored in sealed packaging.
- Avoid direct draughts from doors, fans, or open windows.
- Recheck settings after a power interruption.
- Allow the printer to return to a stable temperature before production runs.
Quick checklist before you run a stronger PETG print
Before starting a part that must hold up in use, run through a short checklist. This helps with brackets, guards, clips, and prototype parts that need both neat finish and dependable strength. If you are printing for a client in Bellville, Paarl, or Somerset West, consistency matters as much as appearance.
Start with a small test piece if you have changed filament, nozzle, or ambient conditions. Then lock in the setting that gives the cleanest bridge without weakening the part. A bit of patience here saves remakes later.
- Fan set to low for the first layers.
- Cooling only increased where the geometry needs it.
- Nozzle temperature confirmed for the filament in use.
- Filament dry, clean, and free of dust.
- Printer area free of draughts and temperature swings.
- Sample print checked for layer bond, stringing, and overhang quality.
