Does anyone have any ideas about these white vertical marks on this grey print? They appear to be were the angle changes but not sure how to get rid of them.
This is the first time printing this model on the Bambu P1S, it used to print fine on my old Creality machine.
I have switched to a brand new roll of filament but the problem remains.
It’s impossible to provide a complete answer to the question without seeing what the model looked like underneath. Also, what filament technology are you using? PLA? ABS? PETG?
If I were to hazard a guess, this may be a contributing factor of the outer walls needing to be thicker, maybe change it from the default of 2 to something like 3 or 4. Also, change the printer sequence from the default outer/inner to inner/outer. This will allow the exterior to solidify sooner so that any interior structures will have less of an opportunity to pull against the outer wall as the wall will be solidified first.
If you would kindly post a sliced version of the model image as it sits on your plate and expose the inner structure. This will yield greater insight as to what the slicer thinks it’s sending to the printer and allow the community to chime in with better advice.
Here’s an example of what would really help. The first screengrab is the default sliced screen.
The second screengrab reveals the model underneath the walls.
Be mindful that Bambu Studio’s algorithm is not exactly Prusa’s even though they are derived from Prusa. Bambu’s secret sauce in their firmware which behaves radically different from Prusa, so one can’t really expect a 1:1 comparison.
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Thanks for the reply and sorry for the lack of detail, I just quickly added it without thinking!
OK I am printing in PLA with 3 walls and an inner/outer wall print sequence.
I have tried reducing the temperature and am currently experimenting with reduced speed to see the results.
Here are the sliced model screen shots:
you could change the grid infill to something that does not cross itself like gyroid and try again
I did consider that, however, the exterior lines do not correspond to where the infill touches the inside wall.
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Thank you. This is very helpful. What this allows us to do is rule out anything to do with the underlying model. This example proves that here is no structures underneath the surface that might influence the model so my earlier guess about wall thickness no longer applies.
Also, don’t forget to clean the carbon rods with IPA and perform the other recommended maintenance. If you’re lucky that will be a quick fix.
https://wiki.bambulab.com/en/p1/maintenance/p1p-maintenance
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Troubleshooting
With the regular pattern of interference here, I’m now leaning towards something mechanical like the belts or pulleys. What is still bothering me though is that there is this consistent pattern which is not easy to explain. I would do visual inspection of the pulley movements especially “listen” to any rhythmic pattern noise that might coincide with the belt positions. Holding a flashlight up against the belts would also be a good place to start as you do your inspection.
Test Model creation
Here is what I might suggest for the purposes of doing some quicker troubleshooting and also to save filament. It’s important to try to recreate a smaller test model that reproduces this error, otherwise you’ll be spending needless hours and filament. This section here looks like a good candidate to cut.
So using this simplified example, using the (C)ut took, chop off the top “hat” of the shape.
Now run your model on just that section and verify that you can reproduce those lines.
If the model section reproduces the error
If you can reproduce the error in your test model, that is great. Now it’s time to change the way the model moves and prove or disprove that here is a drive issue. One way to do this is to take the test model and create a section like this with the cut tool. You will have to pivot the tool 90 degrees along one of the axis and then hit cut.
Once we have our sliced segment, run the test again.
Here’s what we’re looking for. If the lines don’t reappear then we’re back to suspecting the model. In that case, if you have access to the original CAD model, save it as a STEP file and import that. The goal is to change model algorithms which will change how the slicer calculates the vertices it’s trying to slice.
Another thing you can do is also change the model geometry through simplification which will also change the vertices. This is not a solution however, because it will reduce the quality of the model but it will rule in or out the model as suspect.
Here’s how to do that by right-clicking on the model
Then reslice and run the print to verify that the lines have changed. If they disappear or moved but remain in the same orientation, then we likely want to go back to belt tensioning but let’s not get too far since this post is already long enough. Let’s figure out which one of these steps changes a result.
Alternatively, if the lines appear still, then the other test is to rotate the model on the Z axis to an odd number between 10 and 25 degrees. You don’t want multiples of 45 because those angles are coincidental with the belt movement.(it’s complicated)
Alternate filament test
The other thing is to also try another filament on the test model but I highly doubt this will be an issue.
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WOW Olias! Thank you so much for the detailed responses. I will run some more testing today and report back.
I had my own experience with those white lines. It is usually caused by a bad dynamic flow rate calibration. There is too much compensation causing underextrusion in corners. I suggest running the calibration again.
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Well that was a quick fix!! I would never have thought the issue was caused by dirty rods on a machine only 10 days old!!
After a quick clean with alcohol we have a perfect print. Now I will be doing this on a weekly basis.
Thanks for the replies and advice 
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