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peter.l21
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First layer streaks?

Jan 17, 2019 1:34 am

Does anyone know what causes these lines in the first layer print? This is PETG printing MK3 parts. I see occasional cross lines like this in prints - often it looks like waves with very equal distances between the lines which makes me think it's mechanical - but this print is worse than usual. Am I on the right track that this is a mechanical issue? I'm thinking the extruder may be to blame, and if so I am looking for ways to test that.
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tim.m30
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Re: First layer streaks?

Jan 17, 2019 9:56 am

No clue what "lines" you are referring to. I see many lines, some look normal, some look thin, some look thick. All look like normal printing variation. Add variation in light and reflection and normal things can look "different".

Try to better identify what you are seeing that has you concerned.

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joan.t
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Re: First layer streaks?

Jan 17, 2019 10:15 am

If you are getting ripples like those in the sand as the tide goes out.... it probably means your live z is a bit too low... too bid a negative number...


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peter.l21
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Re: First layer streaks?

Jan 18, 2019 4:15 am

tim.m30 wrote: No clue what "lines" you are referring to. I see many lines, some look normal, some look thin, some look thick.
Very very clear diagonal lines - clearly visible in the color change, and very clearly identified by touch.
tim.m30 wrote: All look like normal printing variation. Add variation in light and reflection and normal things can look "different".

Try to better identify what you are seeing that has you concerned.
I thought I had already done that. After years of 3D printing, it stands out - particular because I've never seen extrusion issues diagnoally like this - particulary when it's no repeated pattern.

I don't expect perfect smooth surfaces - with the right light I expect to be able to see the lines the filament was laid down in. What I do expect is that the same surface is "even" meaning showing the same issues all along the surface - not having one part being laid down very different.

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peter.l21
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Re: First layer streaks?

Jan 18, 2019 4:19 am

joan.t wrote: If you are getting ripples like those in the sand as the tide goes out.... it probably means your live z is a bit too low... too bid a negative number...
That may have been closer to the truth (see next reply). I moved the PINDA probe closer to the bed - turns out it was just too close as I had to set the Z adjustment < -1200 to just barely touch the surface, so I moved it back one from there. I think it's actually closer than before because it no longer looks like the hotend touches the plate during the 9 point alignment probes. Before it there was a slight click every time as the tip of the head touched the surface. Which could have clogged up the extrusion a bit. I did full Z alignment and "first layer alignment" to verify everything was fine.

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peter.l21
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Re: First layer streaks?

Jan 18, 2019 4:25 am

I think I have found a solution. As I already posted, I moved the PINDA probe closer to the bed surface and did a full alignment, I then took https://www.thingiverse.com/thing:2780118 and printed it - without modification this printed smooth on all 5 surfaces. I then moved the 4 outer squares to the edge -5mm of top/bottom/left/right and it showed 3 of the 4 corners had issues.

The solution was to manually adjust the bed upwards a bit by loosing the screws on the bed. This was a surprise, as I expected the calibration to do that, in particular in one corner where I adjusted more than 1mm upwards. But I wanted to share my solution so others may get a tip on solving this kind of issue.

With those two changes done, the very clear diagonal lines went away - you can no longer feel a clear difference on the surface, and all test surfaces are super super smooth (like printing the PRUSA logo's first layer).

So it looks like the auto-calibration was very good at the center part of the bed - all the way to about 3cm from each edge. From there I've had to do the calibration print above, and manually adjust until all the extreme squares were printed well.

guy.k2
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Re: First layer streaks?

Jan 18, 2019 8:10 am

This very issue is why some of us are already using mesh bed leveling with more measurement points - compensating for bed irregularities that are missed by 3 x 3 test points. The print surface can have issues that don't match what 3 x 3 with interpolation predicts between or beyond the measured points. Official firmware is coming that will give an option for more sampling points. Meanwhile, you can already do this with custom firmware.

https://github.com/prusa3d/Prusa-Firmware/issues/1239

You need to add custom startup Gcode to activate N7 mesh leveling, but this lets you get a consistent 1st layer over more of your print bed. I find it especially helpful with my 3rd party textured PEI plate. That plate is thinner steel and has irregularities that simply don't match 3 x 3 predictions.

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tim.m30
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Re: First layer streaks?

Jan 18, 2019 7:54 pm

That plate is thinner steel and has irregularities that simply don't match 3 x 3 predictions.
Based on issues people are having with one side bias in leveling, I'm pretty sure that Prusa is using the wrong interpolation for bed leveling. Either an in-house non-linear or a unidirectional choice from Marlin code. The N7 firmware build uses fixed, non-interpolated points, avoiding the interpolation issue.

http://marlinfw.org/docs/gcode/G029-abl.html

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