Micro Layer Shifts

[kvones 5]

Hello all and welcome back!

I have been having a very strange problem recently which I could only describe as micro layer shifts. This only occurs when printing geometric objects with sharp corners, not rounded, more organic shapes. My settings don't seem to make much of a difference. It happens at every print speed, and always in exactly the same places. So much so, that when I hold a print where this has happened next to another one, the layer shifts are in exactly the same place, even if the objects are nothing alike. I have tried everything I can think of: played with the settings, oiled the bearings and rods, re-aligned and re-tensioned the belt pulleys. The Z axis is well greased and it doesn't seem to be the source of the problem anyway. I thought it might be the file, but it has now happened on prints made with different software (and not by me) as well. Is it Cura? Is it the printer? Any input would be gratefully appreciated. I will try and upload a picture of the problem later. These are my settings, with the settings I have also tried in brackets:

0.1mm (0.2mm)

0.8mm

Retraction enabled (Speed 30/ Distance 5.5)

0.6mm (0.8mm)

Density 20% (25%, 10%, 100%)

Speed 40mms (60mms, 20mms)

Temp: 210 (190, 220)

Bed Temp: 70c

Support: None (everywhere)

Platform adhesion: No

Dia: 2.85mm

Flow: 100%

Nozzle: 0.4mm

Travel Speed: 60 (40, 20)

Bottom Layer: 10 (20)

Infill: 60 (40, 20)

Min layer time: 5s

Cooling Fan on

[gr5 2,173]

There's lots of causes for this (a photo would help but I think I understand you - although I can't tell you how many times the problem was "clearly" stated only to see a photo and realize there was a MAJOR miscommunication).

Anyway the most common cause of this effect is when the belts rub against the wood frame. Especially the X axis. Are you having problems with both axes? You can tell if the belt is rubbing because it twists opposite direction each time it switches direction even if it looks like it's not quite touching. Adding a washer to each of the 4 motor mounts sometimes helps and moving the pulley that is on the motor as close as possible to the motor without touching (you need a small gap because once the belt is pulling hard it bends the shaft slightly and the pulley can rub the motor).

I recommend marking each of the short pulleys and the rods on the motors and the other end of the short belts with a sharpie/permanent marker. This way you can see if the pulleys are slipping. While you are at it tighten the hell out of the short belt pulleys - 2 on each axis.

Now there is a tiny possibility you are skipping steps in the stepper. How's the friction? Is it possible someone messed with your acceleration or jerk settings? Jerk defaults to 20 and acceleration I think to 5000. Double check those using the controller. I strongly doubt this is the issue.

Also fyi, changing velocity is unlikely to affect this problem as it is more likely jerk or acceleration that would have to be changed. But instead you should fix the underlying hardware issue (such as loose-ish pulley).

[kvones 5]

Thank you for your reply Gr5! I went back to the belts and had a really good look - nothing was rubbing the wood frame, but one was a little bit off, I have now straightened it. I have also given the bearings another oiling - these two things appear to have made a big difference, and the problem has not surfaced in the last two prints I did. I will do some more prints to see how it goes. I will also add a photo as soon as I can.

Edited April 28, 2015 by Guest

[ilya-sachkov 0]

 

Is it Micro Layer Shifts or may be I have another issue?

[gr5 2,173]

I'm not sure what I'm seeing. Is the bottom of the print on the left side? If so the picture seems to be rotated clockwise and if so then there seems to be a horizontal seam there I think?. I'm really not sure what I'm seeing here.

[kvones 5]

Like Gr5, I am not quite sure what I'm looking at here. But the layer shifts I have been experiencing look more like a single layer having shifted to one side. Sorry I still haven't had time to take a photo, been too busy with work, but I hope this makes sense.

Edited April 29, 2015 by Guest

[gr5 2,173]

I just looked at the picture again! I see it now - we are looking *inside* a box. I thought I was looking at the outside. That horizontal line is probably nothing to do with XY errors but instead is a Z error. If the Z axis moves half as far as it is supposed to move then you get an over-extruded layer and it sticks out a bit like that on both inside and outside. Is that what happened? Sticking *out* on both inside and outside? Like it was too much extrusion? This can be caused also by varying thickness in the PLA filament. Or by temperature changes in the nozzle (hotter temperatures extrude more easily).

[ilya-sachkov 0]

Sorry for the bad foto try to do it better.

I tried to print with different setting (fillament) and nothing helps.

Edited May 1, 2015 by Guest

[TheGuyKnownAsDim3nsioneer 11]

It's irregular horizontal banding. It might have these origins:

- model (check Cura's layer view)

- temperature variation at the hotend (some people got it more steady by applying copper to improve thermal contact between heater block, temp sensor and heater cartridge, others succeeded by running the autopid feature)

- bang-bang mode of the heated bed (UM2); recompile the firmware with activated pid mode for the heated bed

This list might be imcomplete.

[gr5 2,173]

As dimensioneer says it's probably heat or z axis (but could be slicing issues or backlash but probably z axis or heat). First rule out heat issues as this is easiest - watch the temp on the display while it is printing these layers. It should not vary by more than +/- 1 degree. If it moves by 5 degrees during a bad layer then you found the problem.

If not that then it's probably Z issues. With power off slide the bed up and down. Do you feel rough spots? Did you grease the Z screw with the green packet of grease? Make sure the Z nut is held in with 4 screws nice and tight (check by pushing bed up and looking underneath). Could be vertical steel rods also or the linear bearings. Make sure those are still screwed down tight.