Hey everyone,
I’ve noticed a little hiccup on all my prints at one specific z-height, there’s a slight layer shift there, or does look like since it does not look like it would shift only on one side, it is on all side! I haven’t touched anything on the printer, and everything above that spot looks perfect. I can’t spot anything on the axes that might be causing it. Any ideas or tips would be super helpful!
@lkraus Thanks, but my problems happens on PA6-CF, PLA etc. at a specific height, everything else is perfect.
Are you saying if you run a presliced benchy, it will show the line at the same exact z height as that other model?
Or you get a benchy hull line at the spot of the benchy’s floor?
Cuz it looks like a shrinkage/benchy hull line. Thats a googleable phrase for a huge rabbit hole. TL;DR: Large flats tend to shrink differently and more viciously than walls with infill behind them. The layer you transition from mostly walls to mostly floors tends to shrink/cool different. There’s often not a simple solution and is enormously geometry dependant.
That link may still be of value. When you have big flat areas before the model is actually done, the printer slows way down to print the first layer over infill and again on the last layer for best finish.
What this does is adds lots of cooling time to the previous layers which can throw off dimensions and make layers go wonky.
The Bambu tutorial should cover things like adding chamfers and other features, even if not visible, that help make those transitions more gradual to minimize those layer artifacts.
If that specific height comment happens on other models then maybe there’s something else. But if you mean other copies of the same model, or even other models with the same/similar features, then bet it’s the discontinuity in layer print times.
In Studio you can color the rendered images by layer time. Bet you see a big change right at that line.
@Bullocks exactly! This is what I’m saying. A pre-sliced Benchy would cause the same problem. I haven’t tried it yet, but I will now, just to be sure that’s the case. Good idea!
@MZip The thing is… I’m actually perfectly fine with the default values in Bambu Studio, and this layer issue came out of nowhere 4 prints ago. I thought “well, it happens sometimes, but not every time” well, now it does happen every time.
PS: Where do I get a pre sliced benchy? 
If it’s new behavior and that model has printed properly before, it makes me suspect a software or firmware upgrade, or maybe the filament has picked up water if there were no software changes.
Unfortunately, changes to weather and periods of high humidity can change how filament behaves.
In the picture, the shifts correspond to layers with changes in the model— the top of the interior floor, the bottom of the wall notch.
Are you saying that the shifts occur in all models at specific heights above the bed?
Your printer should come with one 
On the home screen select files. There you will find a bunch of preslices files stored on the printer. At the very bottom, there is also a benchy
@Alex_vG Unfortunately not. I deleted them the moment I saw them, and they did not come back after the factory reset.
Oh, I didn’t know that is possible, interesting!
I think, they are also available for download somewhere, let me have a look.
I was able to identify and resolve the issue. I found compressed particles and dust accumulated on the linear rails, which were very difficult to remove. After thoroughly cleaning the rails and lubricating them with the supplied oil from the toolbox, the problem was resolved. The Z-axis linear rail bearings had been rolling over the compressed debris, causing slight movements and affecting theses “shifts” on my printed objects.
Thank you all for your help!
Here is a flawless print, printed using Bambulab PA6-CF
