Prusa MK3S first layer issue with extrusion.

first layer Help issue troubleshooting

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The images attached show the problem: The first layer is inconsistent and the extrusion line splits towards the center of the print. Towards the sides, the print lines are better.

The printer is calibrated, the bed is leveled and the latest firmware is installed.

I was thinking it could be a worn extruder gear, but there are no signs of gear slipping.

I have already tried using different temperatures, z heights and flow settings.
Stock Prusa settings also did not fix the issue.
New nozzle also did not help.

The other layers look fine, the last photo shows an xyz cube.

If anyone has a fix to this solution please let me know.

Thank you for your time

Some of those photos aren't nearly as bad as others.

3s7... combination of nozzle not level to bed and overextrusion.
3s6... hard to tell but nothing looks off to me.
3s5... way overextruded/nozzle too low (the 'sharktoothing' shows the printer is far off the mark)
3s2 not bad, but a tad heavy on the accel/decel... you could increase linear advance to make improve this one
3s1... a bit overextruded/nozzle too low, but not as bad as 3s5
3s3... see 3s5
3s4... looks like an electron microgram of something?

The size of the prints make it hard to tell if something is off with bed leveling/probing. How old is your extruder gear? My original a8 extruder gear has over 1400hrs of printing and 4km of filament under the belt, and still going strong.

So I would say the printer is either due for a recalibration, or something is mechanically off. Trying different z heights and is definitely valid. Sometimes the bed and or nozzle (even framing) may expand and contract differently depending on bed/nozzle temps. So z height is not set it and forget it, other than using the exact same setup for the next print. With an mk3s, you probably have a probe and use mesh leveling. If it's a bltouch, maybe it's getting worn out? Flow settings... I found that different filaments, brands, and colors like slightly different flow rates... variances up to 8% from my experience. Also, mechanically it could be many things. If you have a bearing going bad or worn delrin bushing that might cause this. Also if your frame has come lose or otherwise is moving around there can be problems. Part of my maintenance schedule involves checking tightness on all the screws every 3-4months.

I recommend also to set the bed leveling grid to 7x7 instead of the default 5x5, and set it to measure the maximum 5 samples per point. If you watch the bed leveling and see the printer pause and repeat a measurement of a sample point, that suggests something is under your steel sheet, or a screw or nut got magnetically stuck to the underside of the heat bed and is throwing off the leveling calibration.

Also make sure you dry out the filament. A moisture-contaminated filament flows unevenly, over-extruding sometimes and normal-extruding other times. Put the spool in a sealed container with plenty of fresh dessicant for several days.

Thanks again! very good advice, filament is luckily not the issue. I just received new parts including bearings and an extruder gear. I'll let you know if that fixes it.

I had a similar problem but not at such a small scale. It turned out there was a tiny thread of filament under my build plate, which caused uneven extrusion around that area. So now I carefully wipe off the heat bed every time I remove and reinstall the build plate.

It also looks like your first layer is pulling away from the build plate during the print. Are you using the powder-coated steel sheet? If so, I have found that alcohol doesn't help. Wash it in warm soapy water, rinse it, and dry in thoroughly while touching only the edges, and you'll get better adhesion. There are residual sugar compounds left over from the manufacturing process that alcohol doesn't remove, and they seem to leech out over time. I had to wash my steel sheet about every half-dozen prints over the course of a year before the sheet got "seasoned" to the point where alcohol is all I need now.

Thanks for the help, unfortunately this did not help. Yes, I'm using the powder coated sheet. Thank you for your time

You might try the Prusa forums.

I forgot to ask, is this a new printer or a printer you've been using for a while and just started having problems?

If it's a well-used printer, it is possible that the PTFE tube in the extruder is damaged (it can get "cooked" eventually, resulting in uneven extrusion or jamming). It's pretty straightforward to check: https://help.prusa3d.com/en/guide/how-to-replace-a-ptfe-tube-mk3s-mk2-5s-mmu2s_21664/

I have found the help technicians at info -at- prusa3d.com to be responsive even though they may not be able to solve the problem.

Thanks again for the help. The printer is 3 years old approximately. The PTFE tube was replaced a couple of days ago when I swapped the nozzle. I'll check the forum. Thanks!