Periodic Print Gaps after Adjusting Head  

RE: Periodic Print Gaps after Adjusting Head

Did you perform a Z-axis calibration? Looks like underextrusion but also like your tension is not right.

RE: Periodic Print Gaps after Adjusting Head

@geoper2

If by Z-axis calibration you mean conducting first layer calibration and adjusted Z-height for a proper height of extruded plastic then yes. 

I agree that the regular gaps in the print seems to indicate under extrusion. When I first got my MINI it printed beautifully but then started to jam regularly. Following the guidance I replaced the PTFE tube, raised and secured the hot end and clamped the tube slightly with the upper fitting. Since then I've had this behavior, regular gaps in printing.

Would there be any reason that filament flow rate would be affected by this?

RE: Periodic Print Gaps after Adjusting Head

I am 99% sure that it's a problem with your hotend assembly. Here is a detailed thread describing the same issue: https://forum.prusa3d.com/forum/hardware-firmware-and-software-help/hot-end-assembly/

I had the same problem and only once I replaced the inner PTFE tube and reassembled everything carefully and tightly did I resolve my problem.

It was very frustrating for me because it was very consistent as to where the problem would appear on the print. It would also seem to fix itself when I would switch to Prusament. In the end, I got it working and ran an 18hr print without any issue and several smaller prints after that.

Then my Y-axis belt broke... but that's unrelated. 

RE: Periodic Print Gaps after Adjusting Head

@benji

Thanks, that did the trick.

Now I'm getting banding when I print.

Have you seen this sort of thing and if so what's the fix?

RE: Periodic Print Gaps after Adjusting Head

@travisgood-1

Looks like you posted the same picture. But yes, I have seen that.

I am willing to bet that you still don't have your hotend assembled correctly. There is an official Prusa guide on how to correctly assemble it. Unfortunately, I can't link you right now.

There is also a nice guide by Bondtech. It's for their upgraded heatbreak, but you can apply the guide to stick parts to.

RE: Periodic Print Gaps after Adjusting Head

https://help.prusa3d.com/en/guide/how-to-change-a-heaterblock-heatbreak-mini_122769#123645

https://support.bondtech.se/Guide/0.1+Heatbreak+Upgrade+Kit/60

RE: Periodic Print Gaps after Adjusting Head

Posted by: @benji

@travisgood-1

Looks like you posted the same picture.

LOL! My bad, sorry about that.

Guess I'd lost track of this thread from weeks ago.

Thanks for the subsequent post with links, I'll give them a look.

RE: Periodic Print Gaps after Adjusting Head

Ok, I’ve rebuilt my hotend using both guides several times. No luck!

Is there any more insight in what might be the cause?

RE: Periodic Print Gaps after Adjusting Head

Is the tension screw on the extruder too tight? Are you able to take a picture of it's position? Also by lifting the inspection flap on the extruder is it clean or are there signs of shredded filament?

RE: Periodic Print Gaps after Adjusting Head

+1 Make sure the teeth on the extruder gear are really clean, I use a pin to scrape out each tooth. Tedious, but even a wire brush leaves fragments of plastic in the teeth.

Also maybe check the spool holder is not binding each revolution?

RE: Periodic Print Gaps after Adjusting Head

99% sure your problem is because of a flawed hotend design: https://forum.prusa3d.com/forum/general-discussion-announcements-and-releases/under-extrusion-over-extrusion-clicking-pilling-inconsistent-layers-clogging-unloading-problems-its-probably-all-the-same-core-issue/

Check to make sure the PTFE tube is the right length, you might need to replace it again. From what I have seen, this problem will return over and over, perhaps it might manifest as a different symptom. I THINK I have finally mitigated this problem by replacing my heartbreak with the Bondtech one.