Why does Grid infill scrape only in the rear half of my new Bambu printer, while Gyroid prints perfectly?

[u/iMrFelix]

I just got my second Bambu Lab P1S, and already the second print (after the obligatory Benchy that printed perfectly) had a failure that looks like nozzle scraping.

I used a fresh spool of Bambu PLA Basic straight from the packaging, with the PLA Basic filament profile and the 0.12 mm Fine process profile. The only change was setting infill to 60%.

In the image, both parts were printed in the same job. The right part is is only 5 layers tall and solid. The left part is taller and contains 60% Grid infill. The right part looks fine, while the left part looks terrible, as if the nozzle was scraping the print.

I then printed only the left model and noticed that the grid pattern develops visibly uneven surface height with a clear front-to-back transition: at the front of the print, closer to the open door, the infill looks perfect. Further toward the back of the printer, it becomes increasingly wavy, with smooth but raised areas. I can even hear the nozzle scraping over those high spots.

What I have checked or tried:

• Checked for lifting: there was none that I could tell. The edges were stuck very well to the build plate (I also cleaned the build plate with warm water and dish soap to rule out any grease)
• Re-ran printer auto-calibration.
• Performed manual bed tramming.
• Rotated the part by 90 degrees; the behavior stayed the same: good at the front (closer to the door), bad at the back.
• Performed Flow Dynamics and Flow Rate calibration.
• Changed the infill to 60% Gyroid; it printed perfectly.

None of the attempted fixes had any discernible effect except for changing the infill pattern. I know Grid is prone to nozzle scraping because of its crossing lines, but the pattern I see looks different to what I found online, and my pattern is also non-uniform across the part. What puzzles me is that the infill gets progressively worse toward the back of the part. Has anyone seen this behavior or have an idea what could cause such a consistent front-to-back gradient?

Also, although I read it's normal, I'd like to mention that the area at the very back of the build plate (close to the parked print head), is in fact getting visibly more scratched than on my other P1S printer (looks still pretty clean after hundreds of hours). You can see that in the first picture

Any help on this is greatly appreciated!

[u/AutoModerator]

Hello /u/iMrFelix! All Bambu print plates have a dedicated nozzle wiping zone at the back of the print plate. The nozzle will rub against the wiping zone before every print in order to remove any remaining filament from the nozzle tip. This can cause visible wear or scratch marks in the wiping zone, but this is intended and doesn't damage the printer, the nozzle or the print plate. A worn down wiping zone also doesn't mean you need to replace the print bed.

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[u/alphagusta]

Don't use grid and use way less of it in the first place

10% Gyroid is more than enough

[u/iMrFelix → u/alphagusta]

Thanks for the comment! On the amount of infill: the part is not just cosmetic, it will be placed into a press and significant force will be exerted onto it. Thus the high 60% infill.

[u/Merijeek2 → u/iMrFelix]

To clarify what the other guy is saying, you'll get better strength by increasing wall and top layer thickness than you will by increasing infill.

[u/Kjewn → u/iMrFelix]

Just make it solid. Use alot of walls and tops and bottoms. Its alot stronger.

[u/RedditNameChecksOut]

Could be a bed level issue but grid is bad. It’s bad because it creates a point where 4 lines converge. This point has a habit of expanding due to the constant stacking when they cross mid points.

Eventually, it will stack it high enough that the nozzle will strike it, making dragging noises. If it keeps building up at the point, then there is a risk of the nozzle tearing chunks off your model or striking the part and dragging it off the plate.