Over extruded PLA? what to check?  

RE: Over extruded PLA? what to check?

Where is this "over extruded" portion situated on the print?  Is this the peak?  

RE: Over extruded PLA? what to check?

I find that it looks very similar to the print result in this post related to E3D revo hotend:
https://forum.prusa3d.com/forum/user-mods-octoprint-enclosures-nozzles/revo-micro-installation-on-my-mini/paged/7/

Together with the video from CNC Kitchen ( E3D Revo™ is great BUT has a dirty secret! (REVIEW) )

I believe the "Over extruded" problem is a result of small scale heat creep. It most likely occurred in:
a) a low flow rate condition and/or high retraction frequency layer
b) using E3D Revo or Bondtech heatbreak, which is a better alternative for replacing the original one
c) printing PLA

What actually happening are:
1) The very well performed heatbreak stopping the back flow of heat from nozzle.
2) A rapid temperature change over a very short distance (a few mm) within the nozzle (ref to CNC Kitchen video)
3) When layers are in low flow rate condition with high retraction frequency, a thin clog were formed near the rapid T changing region.
4)  As Extruder keep feeding filament to the hotend with clog, Pressure inside the Hotend/Nozzle rise until the clog moved to the melting zone.
5) You can observe that the nozzle will start under extrusion in those layer for a while, the a lot of filament were push out from the nozzle and become the "over extruded" problem. 

And I find some helpful tips in page 9 of the same post:

Posted by: @pickworthi

@robee-shepherd and @sp4rkr4t - thank you so much. It can be a bit disheartening for a newbie to be faced with a problem like this. 

To re-cap: the issues I have been seeing and the solutions that worked for me are as follows:

Heat creep with PLA. This was solved for me by the E3D version 2 mount. My view is that an unobstructed side to side airflow is the key to this change - although the stock fan does provide a stronger airflow as well. Also, this helped my OCD problem with the Revo fan failing the self test 😉 Hot end over reporting temperature when cooling flow is high - so PLA again. This was identified by Stefan of CNC Kitchen  I found that increasing the Prusament PLA print temperature from 210C to 220C gave me nice smooth surfaces. Given Stefan's findings, I think that means I am actually printing at 210C-215C, which is spot on for Prusament PLA (according to the side of the spool)."Wonky" pillars on the 3D Benchy with PLA. @robee-shepherd hit the nail on the head here, and @sp4rkr4t provided the Prusa Slicer filament setting changes needed (from Prusament PLA profile). For me these were:

a) "Min Print Speed" from 15 to 20 mm/s.

b) "Slow down if layer time is below " from 15 to 5 seconds. and

c) "Retraction length" from default (2.0) to 1.8 mm.

 

Not a problem, but a confusing factor: With any filament that does not have high cooling flow, so basically PETG, ASA and ABS for me, the standard Prusa Slicer provided defaults just work.

With the settings in 3), the head is moving noticeably faster on the small pillar areas of the benchy, and that appears to make the difference, I don't know why reducing the retraction length also helps, perhaps there is an explanation out there.

I now have a PLA benchy printed that is as good as the first benchy I did on a brand new machine with the Prusa provided gcode. A result 😊 

I'm hoping this thread can help others who try the Revo micro out on the Mini+. We are in early adopter territory with this system, so I would expect there to be issues. It's nice to have a community of helpful folk to reach out to. I, personally, have learned a lot.

Hope it may help you too.

RE: Over extruded PLA? what to check?

yes, mostly on the lasts layers (on the fin)

Posted by: @cwbullet

Where is this "over extruded" portion situated on the print?  Is this the peak?  

RE:

I finally had time to do some test, but I couldn't come to a conclusion. This time is a small piece with a lot of retractions. Here are my observations:

After a cold pull the piece comes much cleaner, but the prints quickly start to look bad after 20 minutes of printing.

I tested the samples with the machine hot and cold, and it seems it doesn't make a big difference.

Changing the brass nozzle to a hardened steel one doesn't make a difference either.

After a PID tuning, the problem persists.

Now I'm going to test it again with other filaments, but as far as I remember, the issues appears only with PLA.

I made a macro picture of the cleaning filament after a cold pull. I'm not sure if I have seen something like this before on my machine, but it seems that there is a sign of a problem there.

On the top a piece after a cold pull and on the bottom in a later print.

RE: Over extruded PLA? what to check?

The problem persist, and here is a very suspicious cold pull:

RE: Over extruded PLA? what to check?

Did you ever fix this? and if so, what worked?

RE: Over extruded PLA? what to check?

I'm still struggling a bit. I replaced the heatbreak and the pla prints were noticeable better, but the problem appeared again after some weeks.

I'm guessing printing with PC carbon fiber deteriorates the heater block and that results in a bad sealing. There is some material spill on the top of the heater block sometimes and screwing the heatbreak and the nozzle is kind of difficult lately.

Next step is replacing the heater block for a plated copper one.