My Bambu Lab A1 Mini stopped laying a proper first layer. Not a catastrophic failure, just the kind that ruins every print and sends you down a checklist that does not work.
Everything that did not fix it
I went through the standard advice first, and I want to list it because this is the part that wastes your evening:
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- Changed the filament. No change.
- Fitted a brand new nozzle. No change.
- Ran calibration. No change.
- Tried different STL files, in case the model was the problem. No change.
- Checked belt tension, which is the most common suggestion you will get. Mine was fine.
That is five plausible causes eliminated, and it is where most threads on this problem stop.
What actually fixed it: four bolts behind the hotend
The hotend comes off with three bolts. Behind it, on the rear of the assembly, there are another four. Those four were loose.
I tightened them, put everything back together, ran a calibration, and the printer has produced clean first layers since.
It makes sense once you see it. A hotend that can shift even slightly under load will not hold a consistent distance from the plate, and first layer is the one part of a print where a fraction of a millimetre decides everything. It does not show up as an obvious wobble and it does not throw an error. It just quietly ruins the first layer while every calibration routine tells you things are fine.
If you are troubleshooting this right now
Do the cheap checks first, because sometimes it really is the filament. But if you have changed the nozzle, changed the filament, recalibrated and checked belt tension and the first layer is still wrong, take the hotend off and check those four bolts before you buy any parts.
The whole thing on video
First attempt, working through everything that failed:
And the follow-up, where the hotend comes off and the actual fix happens:
Worth saying: the belt tension suggestion came from a commenter on the first video. It was not the answer in my case, but it was a good suggestion and it is the right thing to check second. If your first layer problem turns out to have a different cause again, say so in the comments so the next person searching this has one more thing to rule out.
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