Retraction in 3D printing: pulling the filament back against strings

Why retraction is needed

Molten plastic in the nozzle is under pressure and leaks out even without extruding. When the nozzle jumps from one part of the model to another, it leaves thin threads behind, called stringing. Retraction pulls the filament back for a moment and pushes it forward again once the nozzle arrives at the new spot. The settings are described in the OrcaSlicer wiki and in the Prusa guide to stringing and oozing.

Length and speed

• Length. With a direct drive extruder roughly a millimetre or two is enough, with a Bowden several millimetres, because the filament runs through a long tube and has to be pulled back more.
• Speed. Too slow lets plastic ooze, too fast can grind the filament in the feeder.
• Too much does harm. A long retraction draws warm plastic into the cold part and can lead to heat creep and a clogged nozzle.
• Material. PETG is stringier and forms threads more easily than PLA, so the settings for them differ.

Links with other settings

Retraction is often combined with lifting the nozzle during a move, see Z-hop. Damp filament makes stringing worse regardless of retraction, so it has to be kept dry, see filament moisture. If threads appear, also look at the nozzle temperature, because overheated plastic leaks more.

What retraction does to the surface. Every retraction leaves a spot on the surface where printing stopped and started again. It may be a tiny dot or a small gap. That is why the slicer minimises the number of moves and travels over already printed areas where it can. A part with fewer separate islands, printed in one continuous pass, comes out with a cleaner surface.

Retraction in your order

We have retraction set up ourselves for PLA and PETG, and you do not choose it in the calculator. We choose these settings ourselves according to the model and material. In the calculator you choose the material, infill strength, scale and number of pieces, and the rest is in the price. Threads are most likely to appear on parts with many fine posts or lattices. If a clean surface matters to you, simplify the shape or write to us.