Burning Extrusion  

RE: Burning Extrusion

That looks like cooked filament is dropping onto your prints and getting melted in. Try this:

1. Raise Z to max.
2. Remove the part cooling fan duct (1 M3 screw at left front).
3. Using flashlight, examine the nozzle and hotend. Look for any build-up of old filament on the nozzle and heater block it screws into. Look particularly for any filament oozing out from the TOP of the heater block.

Hopefully you've just got some accumulated crud building up. If so, heat the nozzle up higher than whatever your hottest filament temp is and use a soft brass wire brush to clean away the accumulation. Be careful around the thermistor and heater cartridge wires. You can use a toothpick or (my favorite) a small strip of corrugated cardboard as well.

Consider using a silicone sock to reduce the amount of build-up on the block, and maybe a coated nozzle to reduce the likelihood of filament staying on the nozzle.

RE: Burning Extrusion

@bobstro

I will try to get a wire brush and do the investigation tomorrow.  I'll update the post with my findings.

RE: Burning Extrusion

Auto parts stores will have them (for cleaning spark plugs). Be sure to get soft brass versions. Buy a few as they do wear out.

RE: Burning Extrusion

A bad brush will hold on to the removed filament. It will get caked.

A good one the filament does not seem to stick to. And is not hard enough to damage the nozzle.

I have had good luck with Amazon ones. Check the reviews. 

RE: Burning Extrusion

Hi @bobstro,

I've removed the cooling duct, raised the temp to 285C and removed the nozzle.  Even with the nozzle installed, it looked like there were air bubbles appearing between the top of the nozzle hex and the bottom of the block.  When I installed the nozzle, I didn't apply the thermal paste as there were no instructions with the Nozzle and the Prusa nozzle replacement video failed to mention about applying the paste.  

As you can see from my photos, the block is pretty dirty.  A year ago or so I had a failure that resulted in a globbed mess of green plastic around the nozzle.  I cleaned it but there is a little bit left up above the red wires but no matter how much I raise the temp, it doesn't dislodge.  I used the brush to clean the block further but there is definitely a build-up somewhere.  I even slid a folded piece of paper in the thin gap on the block at the back and it comes out with the same tar-like residue.

I bought the printer pre-assembled and while it is for work, I'm the only one using it and caring for it.  At the same time, I'm not sure how comfortable I am disassembling it further.  Any thoughts on this, or videos that can guide me on how to clean this?

Thanks.

RE: Burning Extrusion

So while I still wait for the nylon cleaning filament, I further cleaned the heat block with the brush and even lightly stuck a tooth pick up from the open nozzle. It appeared there was a bit of white gunk in there likely from white PLA remains.  I put the thermal paste on the nozzle and reinstalled it and brushed it again.  I did a short print and there was no leaking overcooked plastic.. yet.  I'm going to keep this post open though until I'm sure my woes are resolved.  

RE: Burning Extrusion

there should NOT be thermal paste on your nozzle or in the heat block. EVER. Only on the heatsink side of the heat break.

RE: Burning Extrusion

@vintagepc

Then why did Zodiac provide it?

RE: Burning Extrusion

If it is build up from the hotend dropping, avoid build up by:

Add a e3d socket

Avoid infill with crossing pathes. Per example rectilinear instead of grid.

Increase fan speed. For pet like that sticks well, it helps. But that, you may not want because of other drawbacks.

RE: Burning Extrusion

@ron

So far there hasn't been any more dropping but I will look into the sock regardless.

As for the infill, I typically use gyroid, cubic, or rectilinear.  I've been using grid or triangular over rectilinear lately because rectilinear skips (it's not a solid line, there are gaps in the infill). Not sure if that's normal or just another me issue.

RE: Burning Extrusion

99% of the time when there is inconsistent extrusion and filament dropping onto prints it’s caused by an improperly fitted nozzle. The nozzle must be properly sealed against the heatbreak, not the heat block. There must be no gap at all between them, which as that’s all hidden inside the heat block is easily missed. 
also vintagepc is correct that thermal paste should only be on the top of the heatbreak where it screws into the heatsink and no where else. 

none of the infill patterns should show gaps with normal default extrusion widths and normal volumetric speed values. 

RE: Burning Extrusion

I haven't changed much.  Only on rectilinear infill does the gaps happen. Every single other infill is fine.  I believe the nozzle is fine as it stands now, I haven't had any leakage and I haven't removed it again. I know I shouldn't have the paste around the threads now but should I worry if I haven't had a problem since this morning?

RE: Burning Extrusion

@neophyl

So I've been printing a few little things here and there since I refit the nozzle and its no longer dropping overcooked filament like it was but I still get beads every 20 minutes or so like there's a slow leak.  I'm considering taking the nozzle out once more and reseating it but do you have any recommendations on how to make sure the nozzle is reinserted level? Or is it just trial and error until it stops dropping?