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lbeentjes

Wierd layer mid print

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I dont' know what it is supposed to look like so I'm not sure what is wrong. Do you mean the round ridge approx 1/4 from the dome? I think your pictures are upside down as well.

Did you look at the part in Cura layer view (did you use Cura)? I suspect whatever you think is weird on your part looks the same in layer view. You need to show 2 photos: what you want, and what you got. One of those 2 pictures should be cura layer view. This will tell you one thing, and me 2 things:

1) Is it a slicing problem or a printing problem.

2) What is different from what you want.

 

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If a circle is not round then it's backlash in most cases. Please check that:

- the short belts are tight

- the long belts are resonably tight (you should be able to move the print head around with your little finger when the printer is switched off)

- the pulleys are not sliping (mark the pulleys and the rods with a pen)

You may test the backlash of your machine with https://dl.dropboxusercontent.com/u/15273556/Ultimaker/models/BacklashTest1.stl.

For printing the very top of the dome, you should reduze the temperature significantly and set the minimum layer time to 5-7s (cf. http://umforum.ultimaker.com/index.php?/topic/5651-sphere-problem-with-last-layers/).

 

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You didn't show that the layer view was correct. So I'll have to trust you. But I don't trust you. It's very common for models to have internal walls and for Cura to not know what to do and for it to slice just like this. But I'll assume you are correct...

So... The most likely cause for this - the thing that explains everything is Z movement issues. There is probably something keeping your Z table from moving for a few layers. This explains everything in the photo - it explains the ugly layers where you have overextrusion and filament kind of melting out all over the place (probably worse *inside* the model) and it explains why the upper dome kind of "sunk in" to the lower part of the semi-sphere.

Unfortunately there are many Z related things that can go wrong - you could have something on your machine that is touching the Z platform such that the bed gets stuck during some moves. Or you could need grease or you might have a heated bed cable that is pushing on the bed or you might have a loose Z nut that shifted/rotated such that both the z screw and nut rotated which means the bed wouldn't go down at all.

I would *not* grease or try to fix the issue without trying to find a way to detect it first. I would try turning the Z axes by hand to see if there is a spot where something strange happens (the table stops moving for a moment) around the same height of the nozzle above the bed. Once you can duplicate the problem you can repeat this dozens of times looking around trying to see what is keeping the bed from moving.

I think the most likely thing is the Z nut is too loose.

 

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