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Hollow cube test: top layer not filling in properly - SOLVED

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Dear members,

Lately I see my printer is having problems printing solid layers over an empty space (not sure if it had the same problem earlier). In order to analyze the problems, I followed the advise somewhere else on this forum to print a hollow cube. This is the result:


This print was done at 220 C, normal speed and red filament from UM.

Following tips from this forum I tried to increase speed and lower temperature, same results. I also did a test run with white filament, same result.

I somehow think I'm overlooking a few options, any hints on what other solutions I should try?

BTW, the sides printed pretty OK I think, apart from the blob at the bottom (which was incidental).



Any suggestions would be appreciated.




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I suspect the drawn filament yarns cool down too quickly and then tear off.

- Try to print something slower, with identical temperature, try it at 30 to 40mm /s.

- Try the: bottom-/ top / layer thickness; overall increase slightly.

- So according to the layer thickness of 0.1mm, use 10 to 16 layers (1 to 1.6mm).

- Try to reduce the maximum of the side fan speed greatly, so that the filament yarn can not cool down too quickly.

The standard speed, chosen by Cura, is located at 50mm /s, I think. Regularly meet in accordance with this speed, PLA temperatures up to max. 212 degrees.

If you miss in Cura any adjustment options, then look in the Advanced-/ and Expert-Settings.



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1) Fans are very critical to getting a good top layer. Make sure the fan is working properly and blowing (not sucking) and that the fan is aimed properly to the part you are printing (in other words if the shroud got damaged, repair it with kapton tape). If you printed a different fan shroud, I suggest you go back to the original which is hard to beat.

2) Thicker layers do better because the "string" coming out of the nozzle is thicker/stronger. So try .2mm layers if you are using .1mm layers (try .1mm if you are using .05mm).

3) Many filaments have different characteristics and don't bridge as well. So try changing back to an old filament that used to work or use a filament that isn't too old.

4) As mnis says, use a thick top layer - 1.2mm should be plenty thick (6 layers if .2mm, 12 layers if .1mm).

5) There has been some discussion about some new underextrusion issues in the latest Marlin. I'm not convinced it's real but its hard to ignore all the recent complaints. Nothing specific has been determined at this point. But there may be a new bug in Marlin.


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