[Solved] Under extrusion & cold pull  

RE: Under extrusion & cold pull

I switched back to PLA. Here is the _second_ layer of a print:

To me it is under-extrusion. I do not know what is going on. Default settings in PrusaSlicer. I never had that before, the printer has just been left unused in a box for 6 months.

RE: Under extrusion & cold pull

Problem solved!

I disassembled the extruder and it was clean.

Then disassembled the print head. It was clean too. There was a very thin layer of plastic on the heatbreak where it makes contact with the nozzle. I removed it and also:
* changed the PTFE tube inside the heatbreak: the spare one was 2mm longer than the original one
* screwed the heatbreak a little more in the heatblock so that the nozzle points outward a little more, in order to be absolutely positive there is a firm contact between the heatbreak and the nozzle

After reassembly print quality was back to normal, so I believe this came from the print head. I just do not know why the problem appeared "suddenly". I last printed around Christmas and everything was fine at that time.

Actually I also damaged my extruder. Before all that I played with the idler tension. Seeing no effect I turned the screw to the maximum tension. When I reloaded the filament this must have bent the screw. It was impossible to undo the screw afterwards. The sunk bolt began to turn in its housing. I cut the plastic in order to grip it, not no amount of force would make the bolt and screw turn relative to each other! In the end the hex head rounded. I finally cut the screw with a Dremel, melting plastic ...

Somehow it still works after this repair. I'll have to print new parts sometime.

I am sad this took me so much time. I bought a Prusa in order not to have to tinker with the printer. I regret my Dagoma whose extruder never caused any issue. It had a manual clutch so the filament could be loaded/unloaded manually, it could be actuated even with a cold extruder, would work with any filament with no adjustment at all.

RE: Under extrusion & cold pull

Oh and the screws holding the heatbreak in the heatsink could not be undone too, had to Dremel them.

RE:

Thank you very much jeromejh, I had the same issue for several months now and could't find inforamtions about my problem. I searched a lot like 6 months ago about my problem and couldn't find anything about it.

I hope the problem is fixed now, the first small print looked really good again, and now the next one is 2% done and looks quite well in the first layers too.

Thank you for your advice and good description of the problem.

Friendly Greetings

ManagerLol4

RE:

@jeromejh, did you follow the instructions from Prusa to assemble the hot end:

https://help.prusa3d.com/guide/how-to-replace-a-hotend-ptfe-tube-mini-mini_119449

It is critical to follow the instructions on that website for various tasks to the letter, especially with regards to hot end assembly. If you do, it will work correctly. They update the website with new instructions, especially with regards to measurements and calibration. Don't follow the written instructions that came with the printer.

You can tell by feel when you do a cold pull, while pushing filament by hand when hot, if there is a clog. Once you get it right, remember how much force it takes to push filament through. If it increases at some later date, there is a clog.

The hot end PTFE tube is a wear item in my mind. I replace it once in a while when things don't feel right. You can order spares. If you order a couple boxes of filament, adding small spare parts to the order doesn't increase the shipping cost.

Regards,

Mark