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gaussjordan

Bad layers at specific z-axis range

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Hi there! I've had a blast with my Ultimaker 2 GO. Finest piece of equipment i own!

I've mostly printed flat or small parts so I haven't really noticed the issue until now. More often than not, I get stripes within a specific z range. Not completely broken layers, but it seems like the z-axis steps the wrong height - i get both thin layers as well as fat layers.

11705675_951454078250071_2104495044_o.thumb.jpg.063080c11d61b9456348ee900bbe1aad.jpg

I can see a small scratch in the z-screw, I suspect that could be the cause. The placement of the scratch also makes sense for where the bad layers appears.

What do you suggest I do here? Where can I find a replacement for this piece? Could there in fact be another cause of this problem?

Thanks in advance!

11705675_951454078250071_2104495044_o.thumb.jpg.063080c11d61b9456348ee900bbe1aad.jpg

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Ultimaker will send you a new zscrew (and probably stepper also) if it's bad. But first make sure. Print a few things and see if the lines are at the exact same height. Also with power off try pushing the bed up and down past this area.

This photo is not good enough to see if there is less plastic in this area, more plastic, or plastic sticking in or out or what. It just looks - well - lighter. Try using a cell phone camera - they tend to be able to get very close and clear photos.

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Did you try pushing the bed up and down by hand to see if you can feel a bad spot?

I'm not sure what is going on - it could be temperature fluctuations, feeder, or Z screw. but only Z screw would be repeatable on the same layer every time - but it looked like one of the lines was repeatable and the other wasn't. I'm leaning towards Z but I'm not convinced with only 1 coincidence. See if you can print totally different models (something skinnier) and if it happens at consistant heights. I recommend a 8mm diameter cylinder. With no infill. The goal isn't to make a nice part - it's just a test.

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It could be just mild underextrusion. Caused by filament tangles, nozzle at lower temp, sudden fan increase, things like that. When the filament is cooler it gets more viscous and less gets extruded (the feeder slips a tiny tiny amount - you can see it (barely - need magnifier) in the pattern in the filament through the clear bowden tube).

Also some bad suppliers will sell filament that changes in diameter enough to make patterns like this. The good vendors tend not to have this issue.

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On the cylinder I think the darker areas have higher extrusion and the ligher areas have lower extrusion. I thought it might be your Z axis but I'm not sure because it seems to happen at different layer heights at different times. That nick in your z screw is very suspicious though so you might want to ask support.ultimaker.com to just send you a new z screw to help you diagnose this and there is a reasonable chance that will fix it.

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