Retraction Test

Run a simple two-post (or retraction tower) print with dry filament and a stable baseline, then change only one variable at a time. Tune retraction distance first (and speed second) until strings and zits are minimal, but stop as soon as you see gaps after travel, extruder clicking, or heat-creep symptoms.

TL;DR

Print a two-post retraction test with dry filament, then adjust retraction distance in small steps (speed second). Stop increasing retraction as soon as you see gaps right after travel moves or hear clicking/grinding—those are signs you’ve gone too far.

A quick visual map of the main decisions behind retraction test.

What retraction actually does (and why stringing happens)

During printing, the melt in the nozzle is under pressure. When the nozzle does a travel move (moving without extruding), that pressure can keep pushing plastic out, creating strings and little blobs. Retraction pulls filament back to reduce nozzle pressure before travel, so less plastic oozes out. Too little retraction leaves wisps and zits; too much distance or speed can pull hot, softened filament into the wrong place (heat creep), cause grinding/clicking, or create a delay when extrusion restarts (gaps at the start of the next line).

Baseline setup (do this before changing retraction)

Dry the filament (wet filament strings even with good retraction).
Confirm nozzle is clean and not partially clogged.
Set a sensible nozzle temperature for the filament; too hot increases oozing.
Keep the same filament, nozzle size, part cooling, and print speed for all test runs.
Avoid mixing in other tuning changes (flow, seam randomization, pressure advance/linear advance) so results stay attributable.
In the slicer preview, confirm the model forces repeated travel through open air (posts separated by a gap).

How to run the retraction test (repeatable workflow)

Slice a two-post retraction test or retraction tower that creates frequent travels between separated features.
Start with a reasonable retraction distance for your extruder setup (direct drive typically needs less than Bowden).
Choose a moderate retraction speed and keep it fixed for the first distance sweep.
Print and inspect: strings between posts, and the first 5–10 mm of extrusion after each travel.
Adjust one variable only, reprint, and keep notes of distance/speed/temperature and what changed.
Once distance is close, fine-tune retraction speed; change temperature only if needed after retraction is in the right range.

What to change first (symptom → likely fix)

Strings between posts: Increase retraction distance slightly; if still bad, reduce temperature slightly.
Blobs/zits at travel end/start: Increase retraction a little; if needed, lower temperature a bit. Consider wipe/coast only after basics are stable.
Gaps right after travel: Retraction is too aggressive: reduce distance and/or speed. Add extra prime/restart only if your slicer supports it and only in small amounts.
Clicking/grinding on retract: Lower retraction speed; reduce distance; check filament path friction and heat-creep risk.
No change across settings: Recheck dryness, temperature, cooling, and whether travels actually cross open air (verify in preview). Also consider that the real problem may be too-hot printing or a moist spool.

How to judge results consistently (what to look for)

Strings: Are they thin, sparse wisps that snap off, or thick webs that cling?
Restart: Is the first segment after travel full width, or does it start thin/with a notch?
Endpoints: Are there pimples/zits where travel begins or ends (often near the seam)?
Sound/feel: Any new clicking, ticking, or filament dust at the drive gears during retracts?
Slicer preview: Lots of long, open-air travels usually demand better retraction and/or better travel routing (avoid crossing gaps).

Lock it in (so it stays solved)

After you pick the best result, validate on a small real model that has similar travel patterns (multiple separated features, holes, or islands). Save the profile with filament type plus brand/color (they can behave differently), nozzle size, and extruder setup (direct vs Bowden), since those factors strongly affect the retraction sweet spot.