Retraction has two settings that matter: distance (how far the filament is pulled back) and speed (how fast it’s pulled). Guessing at both together makes it hard to know which one actually fixed — or caused — a problem. A printed retraction tower tests distance methodically while holding everything else constant.
Know your extruder type first
This changes your starting point more than anything else:
- Bowden (motor mounted away from the hot end, filament pushed through a PTFE tube): typically needs 3–7 mm of retraction distance, because some of the pulled-back filament is absorbed by compressing slightly in the tube before the effect reaches the nozzle.
- Direct drive (motor mounted directly above the hot end): typically needs only 0.5–2 mm, since there’s minimal tube length for filament to compress into.
Starting from the wrong range wastes test prints. If you don’t know which your printer has, check the extruder: if the filament travels through a length of tube before reaching a separate hot end assembly, it’s Bowden.
Printing a retraction tower
- Download or model a test object with multiple separate towers or pillars on a single print bed, connected only by travel moves. Several free retraction test models are widely available for common slicers.
- Slice it with retraction distance increasing at set intervals up the height of the print, if your slicer supports built-in retraction towers, or print several versions at fixed distances (for example 1 mm, 2 mm, 3 mm, 4 mm, 5 mm for a Bowden setup) if it doesn’t.
- Examine the result: strings should visibly decrease as distance increases, then plateau. The lowest distance where stringing disappears (not the highest distance overall) is your target: going further adds risk without benefit.
Then tune speed
Once distance is set, retraction speed determines how fast that filament actually gets pulled back before the travel move starts:
- Too slow, and the nozzle starts moving before retraction finishes, so the effective retraction is less than what you configured.
- Too fast, particularly on flexible filaments like TPU, can strip the filament against the drive gear instead of pulling it back cleanly.
A reasonable starting point for most rigid filaments is 25–45 mm/s; increase in small steps and watch for stripped filament (a visible chewed or flattened spot) as the upper limit.