Failure guide
Z Seam Blob Fix
A z-seam blob is a start/stop mark first, not a random surface defect. Put the seam in one visible place, print a small seam tower, and only then decide between pressure advance, wipe/coast, retraction restart, temperature, or seam placement.
Independent third-party notes. Verify firmware, heater, electrical, and vendor-specific work against official documentation for your exact printer.
Start here
The printer is overfilling or oozing at perimeter start/stop points.
A z-seam blob is a start/stop mark first, not a random surface defect. Put the seam in one visible place, print a small seam tower, and only then decide between pressure advance, wipe/coast, retraction restart, temperature, or seam placement.
- Check first
- Force the seam to one rear corner, print the seam tower, and see whether every blob lines up vertically.
- Change only this
- Seam position first. If the blob follows it, tune pressure advance/linear advance or wipe/restart next.
- Verify with
- The seam tower printed twice with the same material, nozzle, speed, and seam location.
- Time
- 5 min setup
- Risk
- Low
- Needs purchase
- No.
Visual diagnosis
Match the visible pattern before changing settings.
Original synthetic diagnostic reference plus licensed look-alike references; confirm with the test or log evidence below.
Looks like this
- Raised bumps line up on one vertical seam or at perimeter starts/stops.
- The defect moves when seam position moves.
- Corners may bulge if pressure advance is low.
Not this
- Random pimples away from the seam are moisture, temperature, nozzle buildup, or over-extrusion first.
- Fine hairs between towers are stringing.
- Missing material after travel means retraction/advance may be too aggressive.
Common look-alikes
- Random blob from wet filament
- PETG nozzle buildup
- Over-extrusion pimples
- Pressure advance corner bulge
- Retraction restart gap
Inspect in the photo
- Does every blob align on one vertical line?
- Does the blob move with seam placement?
- Is the mark overfilled or a missing bite?
- Are random pimples present away from the seam?
Photo cannot prove
- Best pressure advance value
- Whether wipe/coast should be enabled
- Whether the material is wet
- Whether the seam can be hidden by model orientation
Pattern comparison
Does the blob follow the seam, or appear randomly?
Use this before changing retraction. A seam-locked blob and a random blob usually need different fixes.
Blob follows the seam
Bumps stack on one vertical start/stop line or move when seam position moves.
Tune seam placement, pressure advance/linear advance, wipe, coast, or restart behavior. Blob appears randomly
Pimples show up away from the seam, on different walls, or near nozzle buildup/stringing.
Stop seam tuning and check moisture, temperature, nozzle buildup, or over-extrusion.Original visual references
Synthetic examples for fast pattern matching.
These are Print Fixes synthetic diagnostic references, not user-submitted photos. Use them to compare shape and location, then confirm with the test or log evidence on this page.
Licensed reference photos
Compare against real-world photos before changing settings.
These are externally licensed reference photos, not vendor images or scraped forum posts. Use them as pattern checks, then confirm with the small test model on this page.
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Before / after
Compare one small test, not a whole print.
Use the seam tower to prove whether the blob follows the seam; this reference photo is a look-alike, not final evidence.
Download a quick test
Seam blob corner tower
Slice with aligned or rear seam to prove whether blobs follow the seam before tuning pressure advance, wipe, coast, or retraction.
- File
- STL
- Typical time
- 8-14 min
- Material
- Use the failed material; PLA only for baseline seam behavior.
- Dimensions
- 28 x 28 x 45 mm.
- Footprint
- 28 x 28 mm
- Height
- 45 mm
What it testsWhether blobs follow an intentionally placed seam and whether pressure/restart behavior is overfilling starts.
When to use itWhen dots or zits appear near perimeter starts, seams, corners, or after travel moves.
Keep unchanged
- Same seam location unless testing seam placement
- Same temperature
- Same retraction unless it is the chosen variable
- Same pressure advance unless testing advance
Expected good resultA small repeatable seam line with no raised blob and no gap after travel.
Failure result meaningBlob follows seam means seam/pressure branch; random pimples mean material/nozzle/temperature branch.
Slicer notes
- Use aligned or rear seam for the first pass.
- Keep pressure advance, retraction, and temperature unchanged for the baseline.
- Change only seam placement or one pressure setting at a time.
Field guide
Follow the branch that matches your print
Blobs form a vertical line and move when seam position moves
- Likely cause
- This is a true seam/start-stop branch.
- First test
- Slice the seam blob corner tower with aligned or rear seam and photograph the same face.
- Change only this
- Keep seam aligned and tune pressure advance/linear advance or wipe/restart one at a time.
- Verify with
- Repeat the seam tower with the same material, seam location, temperature, speed, and nozzle.
- Stop when
- The mark is smaller, repeatable, and does not turn into a gap or random pimples.
Corners bulge and seam starts look overfilled
- Likely cause
- Pressure is not being reduced early enough.
- First test
- Slice the seam blob corner tower with aligned or rear seam and photograph the same face.
- Change only this
- Run pressure advance or linear advance calibration for this material/nozzle before retraction edits.
- Verify with
- Repeat the seam tower with the same material, seam location, temperature, speed, and nozzle.
- Stop when
- The mark is smaller, repeatable, and does not turn into a gap or random pimples.
The seam has a gap or tiny under-extruded bite after travel
- Likely cause
- Pressure advance, retraction, or restart is too aggressive.
- First test
- Slice the seam blob corner tower with aligned or rear seam and photograph the same face.
- Change only this
- Back off pressure advance or retraction/restart in small steps and reprint the tower.
- Verify with
- Repeat the seam tower with the same material, seam location, temperature, speed, and nozzle.
- Stop when
- The mark is smaller, repeatable, and does not turn into a gap or random pimples.
Pimples are scattered and do not follow seam position
- Likely cause
- This is probably not a z-seam problem.
- First test
- Slice the seam blob corner tower with aligned or rear seam and photograph the same face.
- Change only this
- Check wet filament, hot nozzle, dirty nozzle surface, or over-extrusion instead.
- Verify with
- Repeat the seam tower with the same material, seam location, temperature, speed, and nozzle.
- Stop when
- The mark is smaller, repeatable, and does not turn into a gap or random pimples.
The seam is acceptable but on the front face
- Likely cause
- The fix is placement, not more calibration.
- First test
- Slice the seam blob corner tower with aligned or rear seam and photograph the same face.
- Change only this
- Move seam to rear/corner, try aligned/scarf seam if available, or rotate the model.
- Verify with
- Repeat the seam tower with the same material, seam location, temperature, speed, and nozzle.
- Stop when
- The mark is smaller, repeatable, and does not turn into a gap or random pimples.
Concrete Parameter Range
| Setting | Start | Range | Change when | Stop when | Too far looks like |
|---|---|---|---|---|---|
| Seam position | Aligned or rear for diagnosis | Aligned/rear/corner for testing; avoid random until diagnosis is done | You need to prove whether blobs follow the seam | The blob location moves with the seam or the seam is hidden on the part | Overdoing this hides the seam but creates gaps or random scars. |
| Pressure advance / linear advance | Current material/nozzle value | Retune per material and nozzle; use the slicer or firmware calibration pattern | Corners bulge or seam starts are overfilled | Corners sharpen without gaps after travel | Too much creates gaps or weak starts after travel. |
| Retraction distance | Printer profile default | Direct drive often 0.4-1.2 mm; Bowden often 3-6 mm | Blob occurs after travel and pressure advance is not the main signal | Restart is clean without grinding, gaps, or clicking | Too much causes grinding, heat creep, or restart gaps. |
| Wipe / coast / restart extra | Off or profile default | Small steps only; slicer names and units vary | A small overfill remains at perimeter end/start after pressure is close | The seam shrinks without holes or underfilled starts | Overdoing this hides the seam but creates gaps or random scars. |
| Nozzle temperature | Known-good material range | Test 5 C lower only after seam behavior is proven | Ooze and random pimples appear with glossy strings | Blobs reduce without weak or matte layers | Overdoing this hides the seam but creates gaps or random scars. |
Material / Machine Differences
PETGOften leaves glossy wisps and nozzle buildup. Prove seam behavior before blaming retraction.
Silk PLACan show shiny seam scars when printed hot. Temperature and pressure behavior both matter.
Direct driveUse short retraction values; pressure advance and restart behavior usually matter more than distance.
BowdenLonger retraction may be normal, but too much can cause delayed restarts and gaps near the seam.
Klipper / Marlin advancePressure/linear advance values are material, nozzle, and speed dependent; retune after hardware or filament changes.
Wrong Turns
Leaving seam on random while diagnosingYou cannot tell whether blobs follow the seam or are random extrusion defects.
Increasing retraction until the blob disappearsThe seam may turn into a gap, clicking, heat-creep symptoms, or weak restart.
Copying pressure advance from a different printerCorners, seams, and infill starts can all get worse because the value is not portable.
Using coast/wipe to hide wet filamentRandom pimples remain and the seam test gives a false improvement.
Stop tuning when
Do not keep chasing perfection after the signal is clear.
- The seam tower shows a small repeatable vertical mark, not a raised blob.
- Moving seam position moves the mark, proving the branch.
- Further pressure advance or retraction creates gaps after travel.
- Random blobs remain after seam improves; switch to material/nozzle diagnosis.
Common setups
Jump to the branch that matches your machine or material
OrcaSlicer pressure advance blobs OrcaSlicer, corner bulge, seam dots, direct drive or Bowden Run seam tower with aligned seam, then pressure advance calibration. Run PA calibration only after seam position proves the blob follows starts and stops. Bambu Studio seam placement Bambu Studio, visible front seam, otherwise healthy part Move seam to rear/corner or try scarf/aligned seam options where available. Move seam to rear/aligned and check if the blob follows before PA changes. PrusaSlicer rear/aligned seam PrusaSlicer with visible start/stop scar Use rear or aligned seam before wipe/coast/retraction edits. Use rear/aligned seam for one tower before enabling random seam.
Copy before changing more settings
Z-seam diagnostic brief
Fill this out after the first test so the next branch is based on evidence, not memory.
Submit this failure patternPrinter:
Slicer:
Firmware:
Material:
Nozzle size/material:
Bed surface:
Exact symptom:
Recent change:
First test run:
One change tested:
Result:
Next branch:Still not matching?
Jump to the next likely diagnosis
Problem Pattern
Use this page when bumps line up on a vertical seam, appear at perimeter starts, or move when seam position changes. If blobs appear randomly across the part, treat moisture, nozzle buildup, over-extrusion, or temperature as the next branch instead of tuning seam settings.
Likely Causes
- Pressure remains high when the nozzle starts or stops a perimeter.
- Pressure advance or linear advance is too low, too high, or not tuned for this material/nozzle.
- Wipe, coast, restart extra length, or retraction settings create a small overfill at the seam.
- Seam placement puts a normal start/stop mark on a visible face.
- Random blobs are being mistaken for seam blobs when wet filament, nozzle buildup, or high temperature is the real branch.
Print Context
- Applies to
- OrcaSlicer, Bambu Studio, PrusaSlicer, Klipper pressure advance, Marlin linear advance
- Best first move
- Force the seam to one visible rear corner and print the seam tower.
- Do not start with
- Random seam, more retraction, and pressure advance changes all at once.
Recommended Checks
0/5 done Start with the first check. Keep this page open while you test. The checklist saves on this browser so you can come back after the print finishes.
Verification
- The seam tower shows a smaller, more consistent vertical mark on the same seam face.
- The blob moves when seam position moves; if it does not, switch diagnosis.
- Pressure advance or linear advance changes improve corners without creating gaps after travel.
- A normal part keeps the seam hidden or acceptable without random surface pimples.
After the test
Use the result, do not keep changing random settings.
If one check clearly changes the print, repeat that exact test once before moving on. If nothing changes, switch diagnosis instead of stacking more slicer edits.
Warnings
- Too much pressure advance or linear advance can create corner gaps, weak starts, or under-extrusion after travel.
- Too much retraction can grind filament, cause heat-creep symptoms, or create restart gaps.
- Random seam placement can hide a diagnostic pattern and make the surface look dusty.
- Coast and wipe names vary by slicer; change one feature at a time and keep a profile backup.
Useful when
- Blobs that line up on one vertical seam or move when seam position changes.
- Tuning pressure advance, linear advance, wipe, coast, restart, or seam placement with a small repeatable test.
Skip if
- Random pimples across the model that do not follow the seam.
- Wet filament, nozzle buildup, or over-extrusion that affects every surface.
More traps to avoid
- Using random seam while trying to diagnose whether blobs follow the seam.
- Changing pressure advance, retraction, wipe, coast, and temperature in the same test.
- Copying another printer's pressure advance or linear advance value as a final answer.
Bench Note
Page: Z Seam Blob Fix
Printer / firmware:
Slicer profile:
Filament brand and material:
Nozzle size:
Bed surface:
Recent changes:
Result to compare next:FAQ
How do I know it is really a z-seam blob?
Force the seam to one rear corner and print the seam tower. If the blob forms a vertical line and moves when the seam moves, tune seam and pressure behavior. If blobs stay random, switch to moisture, temperature, nozzle buildup, or flow.
Should I tune pressure advance or retraction first?
Tune pressure advance or linear advance when corners bulge and seam starts look overfilled. Tune retraction/restart/wipe when the blob happens after travel moves or at perimeter restarts.
When should I stop tuning the seam?
Stop when the seam is small, repeatable, and hidden on a less visible face, or when another setting starts causing gaps, weak starts, clicking, or rough surfaces.