Missing printing layers

[cloudsforest 0]

I've been trying to print models using my Ultimaker 2+, and the printed models always miss one or two layers, leaving a very big gap on the sample.

I wonder what could be the reason, and how to troubleshoot it. Thank you.

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Edited December 4, 2017 by Guest

[gr5 1,270]

Unfortunately lots of things can cause this.  First make sure that cura doesn't also show a missing layer - often this kind of thing is caused by a tiny hole in the model (a bad model).

It could be a filament tangle.  But the two parts in the top photo seem to have the problem at the same height.  Do you agree?  If so then it's a "Z" issue:

When the Z axis moves, if it doesn't move far enough, it will overextrude on that layer.  If it moves too far then you get a gap.  

with power off you could try moving the bed up and down to see if you feel anything.  Usually the problem is fixed by cleaning the Z axis screw but it could be many things (stepper driver too hot, screw, nut, vertical rods, vertical bearings).

Putting a 1kg weight such as a brick in the back of the bed once it starts printing can sometimes fix these issues or move them elsewhere.

The helix is triple so if you use a toothpick and clean while spinning the screw you will miss the other 2 helixes.

I recommend spending at least 2 minutes with a toothpick and tissue.  You can certainly afford 2 minutes as a test, right?  concentrate near the top of the screw where you are having problems (you only seem to be using the top 6cm so why clean the whole thing?).  A proper cleaning involves removing the stepper and Z screw - very easy to do - the hardest part is unplugging the cable (assuming um2) (you have to remove a cover - no big deal).  Then place on newspaper and spray with WD-40 and clean it completely and let dry and put ONE tiny drop of grease on it after.

While the screw is out test the bed movement and see if there might be a problem with rods and/or bearings.

Edited December 6, 2017 by Guest