Strange print artifacts - horizontal bands / rippling

[drumrboy44 0]

Ok, I finally got my (new, assembled) machine printing after an unexpected nozzle plug, but it appears that all of my prints have the same strange (to me) print artifacts that I have attached pictures of below:

Does anyone know what might cause this? It is on every print I have, and you can feel the edges of each horizontal band. I purchased my second ultimaker fully assembled, and even the test print that Ultimaking included with my machine contains the lines (though slightly less pronounced). If you view edges of prints with this artifact, there is a "rippling" effect, as the alternating bands seem to be of different thickness.

I would greatly appreciate anyone who knows how to solve this issue, or any suggestions anyone has!

Thanks!

 

[illuminarti 18]

This look to be related to the z-screw - are the bands 3mm apart - the pitch of the z-screw?

If so, I'd check if the z-screw is seated properly into the coupling, and is vertical. Watch as you use the ulticotroller or computer link to run the platform up and down - is the top of the z-screw wobbling noticeably?It should be straight and not wobble, and be well seated into the coupler, otherwise the bed is going ot shift slightly as the screw rotates.

It's hard to totally remove all traces of the z-screw pitch effects, but this is particularly bad in your case, judging from the photos.

 

[drumrboy44 0]

Okkk, it pretty clearly is a Z screw issue. The screw wobbles rather noticeably when running the platform up and down. This is what my z coupling looked like when I received it.

Is the gap below the z coupler normal? I figured maybe not, so I loosened the screws and lowered the z coupling into the circular cutout, but not so far down so it touches the motor below. It now looks as follows:

 

However, when I retightened the screws and ran the platform up and down, there was still a noticeable wobble. A test cube I printed looks like this:

 

 

It may be SLIGHTLY better than my previous print rippling (See ), but it is certainly far afield from quality I have gotten from a previous ultimaker I owned. Look at the difference between the two prints:

 

Does anyone have any ideas for fixing this problem? what is the correct position for my Z coupling, and why would it have such an effect on the Z wobble?

 

Any help is very much appreciated!

 

[illuminarti 18]

I think that the Z-axis screw needs to be moved down so that it is seated on the coupler, and the thinner part is pretty much hidden inside the coupler.

 

[gr5 2,172]

I'm sure many things could cause this so I will come up with a single theory:

Are you familiar with the "universal joint" on the axle of a car? it looks like this:

http://ode-wiki.org/wiki/images/8/8f/Universal.jpg

In that picture if body1 is rotating at a constant speed and the angle isn't straight, body2 will speed up and slow down 4 times per rotation (2 speed ups, 2 slow downs). If the angle is straight, body2 rotates at a constant speed. The stronger the angle, the worse the problem (for front wheel drive cars they invented the CV joint as the angles are more of a problem in front wheel drive).

Anyway, I'm thinking a variant of this problem where something isn't coaxial. So check your z axis motor and make sure the 4 bolts are tight and there is no gap. looking under the UM at the motor check for gaps between each corner of the z motor and the wood.

If that seems fine then instead try loosening the 4 bolts holding the motor, loosen and retighten the coupler. Then retighten the 4 motor screws one more time.

Also what Illuminarti said: the z axis screw is not inserted all the way into the coupler anymore and that seems like it might be part of the problem. Or maybe that made things better? But that's messed up. Normally the screw is supposed to be inside the coupler. Not resting on it.

Also did you grease your screw with the "green" grease when you assembled the UM?

Make long moves with the Z axis using Cura or pronterface and see if you can see it speeding up and slowing down or wobbling or something.

Another possibility is the entire problem is somehow related to the bed itself and you playing with the zcoupler just happened to move something in the bed that made it better.

That's all I can think of right now.

 

[Nicolinux 288]

Hey drumrboy44, do you have any updates on this issue? I think I have the same problem:

http://umforum.ultimaker.com/index.php?/topic/2716-cannot-lower-bed-to-reach-endstop/

Stefan

 

[drumrboy44 0]

What I ended up doing was reseating the z coupler a few times (all the way up against the beginning of the screw threads), and it greatly reduced the effect, but did not eliminate the problem completely. Then I got distracted by another issue. I eventually had plans to reseat the Z motor itself, to see if that was what was causing the wobble in the z screw and the print artifacts.

 

[Nicolinux 288]

But how will you move the z-motor? You would have to move it only a few milimeters to the side and there is no place for new screw holes without touching the old ones. It may be better to move the brass nut. That's what I tried (see my previous thread) but due to printer inaccuracy the whole z-stage was skewed. I am back to the original parts now, but I am still not sure how to tackle this issue.

 

[Nicolinux 288]

Ok, just for the record - if anyone stumbles over this post. My issue was solved by making the brass nut sliding around left and right. This way it could accomodate the offset to the right of the threaded rod.

http://umforum.ultimaker.com/index.php?/topic/2716-cannot-lower-bed-to-reach-endstop/