The top sinks, has a grid texture, or has little gaps between the lines.
It happens on any FDM printer. Setting names are Bambu Studio's: in Orca Slicer almost all have the same name, and PrusaSlicer or Cura usually have an equivalent.
Where do I start?
Two questions to sort out what to check. It's a guide, not a sure fix: every printer and every filament is different.
Check in this order
- The printerIf it printed fine yesterday and not today, it's almost never the profile. Check the plate, the nozzle and the room: printing at 15 °C is not the same as at 30 °C.
- The filamentA spool that has soaked up moisture gives strings, bubbles and brittle parts. Dry it before changing settings, and pick that filament's profile in the program.Filament pages
- The quick checksThe “First” list below: it's the fastest to check.Go to “First”
- The slicerOnly now, the settings below, in order. Change one thing, print a small test and compare. If you change three at once and it gets fixed, you won't know which one did it.Go to the settings
Check in this order
- The quick checksThe “First” list below: it's the fastest to check.Go to “First”
- The filamentA spool that has soaked up moisture gives strings, bubbles and brittle parts. Dry it before changing settings, and pick that filament's profile in the program.Filament pages
- The testsCalibrate your filament with these tests:2Flow
- The slicerOnly now, the settings below, in order. Change one thing, print a small test and compare. If you change three at once and it gets fixed, you won't know which one did it.Go to the settings
Check in this order
- The quick checksThe “First” list below: it's the fastest to check.Go to “First”
- The previewStep through the slicer preview layer by layer: that's where you spot missing supports and odd areas in this part.
- The slicerOnly now, the settings below, in order. Change one thing, print a small test and compare. If you change three at once and it gets fixed, you won't know which one did it.Go to the settings
First
- Dry the filament: moisture also leaves the top rough and full of gaps.
- Check whether the open lines are only on the top or all over the part. If it's all over, it's short on plastic: calibrate flow before touching the top.
Then, in the slicer (in this order)
- Flow ratioFilament › FilamentIf there are open lines all over the part too, it's short on plastic: calibrate flow and store the result here.
- Top shell layersProcess › StrengthWith few layers, the top sags onto the infill. Add 1 or 2.
- Minimum fan speedFilament › CoolingThe top lines are laid over the infill, almost in the air, and need to cool fast so they don't sink. On a long layer like the top the fan runs at its minimum: with PLA, keep it at 60% or more.
- Infill densityProcess › StrengthWith very low infill, the top has nothing to rest on.
- Top surface patternProcess › Strength“Monotonic line” gives the most even top.
- Top surface speedProcess › SpeedSlower, the beads come out more even. It's a single layer, so it costs little time.
- IroningProcess › QualityFor a smooth, shiny top, an extra pass irons the lines flat. It doesn't fix a sagging top.
Fixed by calibrating:2Flow
Tried everything and it's still the same? Calibrate your filament with the 8 tests, or write to us with a photo.