Prusa Mendel I2... Z axis problem?

Hello and sorry about my bad english

I just finished to build my Prusa mendel, I did all calibration, printed some test (cube) perfect size, but...
I have this kind of problem when I print high stuff:

[www.youtube.com]

As you see in the video see the perimeters been pushed by the hot-head as it's the plastic is high it's happen not on all perimeter.
I don't know if I was clear but I'm new on this stuff maybe it lost some steps? Or maybe is too Hot or the feedrate E
I use Slic3r with 0.5 or 0.35 nozzle on both case still happen, I tried "extrusion multiplier" different value notting change.

I calibrated everything and I double checked, so please people with more experten than me...
Have you see this problem before??
Please let me know

Thanks
Carlo

Are you sure your Z motors couplings are not slowly letting go the threaded rod down ?

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Most of my technical comments should be correct, but is THIS one ?
Anyway, as a rule of thumb, always double check what people write.

Hi,
No...pretty sure I checked Z motors couplings before print something.
Other tips

Thanks
Carlo

It's hard to tell from the video but it seems the layers are not lining up occasionally in the y-axis. It might be either skipping steps or the gear is slipping in the y-axis.

Here I posted few images...
I don't understad why if I print a cylinder is perfect, layer over layer...
but when I start to print something with more curve as "the pink lady"
IT start to overlap the layers badly.

... seems the wall isn't stable/rigid enough - maybe you should print with more perimeter shells ...

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Viktor
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Hi Viktor....good idea, I'll try tonight.
Thanks
Carlo