Horizontal lines on prints Ultimaker S5

[balint 1]

Hello, I'm opening this thread to hopefully solve my issue with the quality of my prints and specifically the one that has been going for a bit over 2 days and still going for 1 and a half. My print have these vertical lines on the side which given the print time I refuse to accept.

I'm printing with PLA 2.85mm from Filamentum
The main settings are as follows:
layer height: 0.2mm

infill: 20% grid with NO infill before walls 

build volume temp: 30C
print temp: 200C
Flow: 99%
speed: 35mm/s
print accel.:3500mm/s2
jerk: 20mm/s
 

If you are interested in anything else please leave a comment

The first image was taken yesterday, the second today a few minutes ago. They are the same print.
I'd appreciate any help or guidance to improve overall quality and to put an end to these lines. Note that the print is 2 parts of a Möbius slip, so  the surface changes shape with every layer in every direction.
Thanks in advance!

[balint 1]

@gr5

[Framar 38]

Well, this looks like what we get with our S5 when using a 0,8mm nozzle...

[balint 1]

I'm printing with .4 nozzle

[gr5 2,172]

So I'm pretty sure you mean the horizontal lines, right?

 

Those can be caused by varying nozzle temperature or by Z issues.  I'm 90% sure it's Z issues but you might want to go into the TUNE menu and look at the nozzle temp.  If it's caused by temp you will see the temperature vary by at least 8C peak to peak.  If it stays near goal temp within 3C then it's not temp issues.

 

More likely your Z axis isn't moving consistently.  Make sure z-hop is turned off.  If z-hop is enabled then that could explain everything right there.  z-hop should only be used on delta printers for the most part.  And printers with really really good repetitive Z movement.

 

I leave the most likely issue last - something with the Z screw and nut.  I'd try cleaning the z screw.  It's a triple helix so make sure you get all 3 helixes.  I would do a quick 4 minute clean and if that helps then I'd take the z stepper and z screw out the bottom of the printer and really clean it well.  For the quick cleaning use a toothpick maybe to get most of the grease and dirt out of the 3 helixes.  You can just do the top few inches of your z screw as that is the only portion used for the print in your photo.  I like to use a paper towel and a very small screwdriver to clean out the grooves.

 

It could be that the Z nut or screw need replacing. Some are better quality then others.

 

Another trick is to put a brick at the back of the print bed but you can't do that with an S5 because of the auto level.

 

In case you didn't get it: imagine the bed moves down 0.2 most of the time but somtimes it moves down 0.15 and then when it extrudes expecting 0.2 space it squeezes out all around the edges (over extrudes) and then on the next layer it moves 0.25 (0.2 plus the 0.5 that it hadn't quite moved on the previous move) now it underextrudes by 1/4.  So you get horizontal lines that stick out or in.

[balint 1]

Thank you so much for your reply, my nozzle temp hits the target spot on, however I tried multiple temps (200-210) on prints and since yesterday I set it to 198 and it seems to be much better. 

 

As for the z-screw, I'll check when my prints for my current project are done and report back. 
Thanks again,
Balint