Kossel linear plus: repeatable failure at specific height

[Bids]

Hi,

I have been having a repeated issue with my Kossel (that otherwise works just fine): when I print a model that is high enough, at a height of exactly 5cm, the print starts failing: I hear a few subtle and intermittent licking noises, and from there on the layers are very poor quality and do not adhere to each other.

It seems like I am losing/skipping steps at Z=5cm, whichs messes a layer or two completely, and then all upper layers are not good.

Picture below, you can clearly the layer where things went sideways. I ruled out a problem in the G-code, this happens on pretty much all models I tried that are high enough to cross this 5cm value.

I inspected the rails, no mechanical issue, and anyway the kossel being a delta printer, a mechanical issue on one axis would not give a problem at a very precise Z height.

I put two failed prints of two completely different objects side by side, and the problem occurs within the same millimeter on both, i.e. at Z~5cm

I’m puzzled as to what can be the root cause of this ? What elements could possibly explain an issue that would repeatably occur at a given height ?

Thanks,

[Zapaer]

@Bids,

Need more info to help you out on this one. Could you upload photos of the printer so that I can see your overall layout.

Also, please upload the stl model that you printed along with the gcode or factory file.

Finally, this might be of use to you:

https://www.simplify3d.com/support/print-quality-troubleshooting/

- Zapaer

http://www.zed3d.ca

[Bids]

Hi @Zapaer,

First of all I am very sorry I did not reply earlier: somehow I did not get email notification of the reply, and did not check here.

Here is a photo of the printer, nothing special/fancy.

I have the STL and gcode but the site will not let me upload anything else than images (probably due to my account being very new)

I was printing this napkin holder from thingverse

I did check the G-code in Camotics, and it is OK, no visible shift/data corruption visible anymore up to the top of the model.

In the meantime I have done several other tests, and first concluded that this problem is in fact not related to reaching a specific height, because I printed successfully a 15cm tall object, with a 1cmx1cm square base.

HOWEVER, I have now come to the conclusion that this problem appears whenever my print exceed 5 hours, whatever I am printing: everything goes fine until ~4h45 have gone by, and sometime between 4h45 and 5h of print time, I start hearing the head slightly bumping into a part of the previous layer, first very subtly, and then it becomes more noticeable. Which produces a poor quality layer, therefore the next one is worse, until it becomes as shown in the original picture.

I thought about a driver issue linked to overheating over time, but the timing of ~5h is so repeatable that I do not believe this is it.

I ruled out a calibration issue of the machine, where small errors would accumulate and become larger as height increases, because the 15cm tall object printed just fine.

Any clues or ideas what to test next to figure out what happens ?
Each try takes about 5 hours, so obviously the investigation takes forever

Thanks,