Blobs Cause Print Head to Knock Object Off Bed  

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APEGamer
(@apegamer)
Active Member

It appears that everything is dialed in and the printer is working great except that it frequently drops a blob onto the print. The next time the print head moves over that spot, it knocks the print off the bed.

It happens frequently enough that I have yet to get a successful print of anything more than just a couple minutes. This is Prusa PLA filament, I used Slicer .15mm quality, 15% infill. The printer is an MK3S with the upgraded components. This was a problem before the upgrade, and I hoped the upgrade would correct it, but it did not.

Ideas, anyone?

 

 

Posted : 22/12/2020 6:19 pm
mGoleta
(@mgoleta-2)
Eminent Member

I found this also to be the case.  What I found effective is cleaning the outside of the extruder nozzle with a wire brush before printing.  Small brass brushes are readily available online.  I set the unit to preheat and raise the z axis so that the nozzle is easy to reach.  A few wipes with the wire brush removes the leftovers from the last print job.  Be attentive not to brush the thermistor on the side of the hotend.  I try to stick to the area just around the nozzle and the nozzle itself.

Posted : 23/12/2020 12:00 am
mGoleta
(@mgoleta-2)
Eminent Member

The other issue I see when printing with PETG is strings if the retraction setting is too small.  This builds up small amounts of reside on the nozzleand strings when moving across the build plate to a new spot.  Cleaning the nozzle before printing and setting retraction higher has let me do prints that typically take 4-6 hours.

Posted : 23/12/2020 12:07 am
JoanTabb
(@joantabb)
Moderator

there are two common causes for blobs with PETG

1, incorrectly fitted nozzle causing leaking above the heat block, cure...   re fit the nozzle correctly, so that it tightens against the heatbreak, not the heatblock
2, the nozzle tends to pick up particles of petg, as it prints, if the flow rate is too high, or the extrusion multiplier is too high.

flow rate is normally set to 95% for layer heights 0.07mm and higher. (Inside the Prusa Start Gcode)
(this line      M221 S{if layer_height<0.075}100{else}95{endif}      )

if your filament is oversize, or the slicer settings are set undersize, you can get over extrusion which will precipiate this problem...  
you can reduce the liklihood be reducing the extrusion multiplier bay say 5%    (From 1       to    0.95)     or by reducing the flow rate to say 90%

you can get away with slight under extrusion earier than you can manage slight over extrusion...

regards Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK...
Posted : 23/12/2020 12:24 am
APEGamer
(@apegamer)
Active Member

I'll try this tonight. As a reminder, I'm using PLA, not PETG, though. I'm guessing it doesn't matter.

Posted : 23/12/2020 12:48 am
Peter M
(@peter-m)
Prominent Member

Lower temperture,

and/or

Extrusion multiplier lower.

Every filament is different!

Posted : 23/12/2020 12:43 pm
APEGamer
(@apegamer)
Active Member

Ah, here's the problem. I don't know why I didn't see this before. It looks like I'll need to take the foopin' thing apart to see the root cause.

Thanks for all the fastidious input here.

This post was modified 4 months ago by APEGamer
Posted : 23/12/2020 6:05 pm
JoanTabb
(@joantabb)
Moderator

@apegamer

glad to help!

Joan

 

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK...
Posted : 23/12/2020 8:48 pm
Carbu86
(@carbu86)
Active Member

augmenter la vitesse lors de première couche fonctionne aussi

Ewellix LBBR8, gate 9mm, poulie powergrip, mmu2s...
Posted : 23/12/2020 9:59 pm
Carbu86
(@carbu86)
Active Member

Vu la photo effectivement il y une petite fuite 🙂

Ewellix LBBR8, gate 9mm, poulie powergrip, mmu2s...
Posted : 23/12/2020 10:13 pm
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