PETG-HF bleed through using PLA as support

[user_fish]

I have nearly cracked all my problems with this print thanks to this forum but I still have this one last remaining issue that I hope someone can help me with…

I am printing a large flat item that takes up around 80% of the plate (9mm thick) in BL PETG-HF which has been dried recently and stored in the AMS. I have been using PLA as the interface layer as it means I get easy separation and a clean finish which is crucial for where other parts slot into the finished item. Before I resolved my other issues this was working quite well but has recently started to play up more often and becoming more difficult to separate and causing the scaring in the photo. With all the problems that have appeared, I am wondering if the tuning I have done to resolve other issues is now making this worse, the main one being turning off the part cooling and auxiliary part cooling fans to zero fans.

I have tried printing without the whilst this is a bit better on the large area pictured it is not so good for the critical slots where the parts join. There is still an issue where it is quite difficult to separate but i did use concentric interface layer and increase the Top Z distance a bit to 0.2mm but still no joy so it looks like the PLA interface is the answer but the issue I am getting can be clearly seen in the capture below from the timelapse.

Ideally I think I would like to be able to use PLA interface for the smaller areas and not for the larger one but I don’t believe that is possible?

The other smaller PLA interface bits here do not seem to have the issue and print perfectly.

[user_fish]

I meant to add that I am presuming it is down to the infill pattern of the support and the dragging caused by the change in direction of the next layer causing the clumping (which I resolved by using Gyroid in the main body) as per these two pics:

I am just not sure why, is the chamber temp getting too hot and could I pause just before this change in direction to allow enough time for the heat to dissipate maybe? Or is there a better infill pattern to use for the main support when using standard style supports?

[Bullocks]

Just adjust the support base pattern spacing to form those ribs a little tighter

The defect could be lots of things including wet filament, incorrect cooling, too high temp, too small of support interface line width, etc. can sidestep it by pulling those ribs close together and reduce the gaps.

[user_fish]

Thanks, that is a good call, I did not see that you could adjust the spacing.

I think I may have found the issue though, I realised that the Part fan was off so enabled it from the printer control and it instantly fixed the issue. I later found that the PETG profile had the fan set to very low speeds which I must have mistakenly changed when I was trying to fix the other warping issues.

Here is a pic showing where I enabled the Part fan…