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Filament Deflecting Upward on Extrusion  

New Member
Filament Deflecting Upward on Extrusion

Hi All,

Looking for some troubleshooting assistance with my Prusa MK3S. I've been printing without issue for a few months. However, I recently ran into some 1st layer adhesion issues. After working to tune with Live Z Adjust for some time (longer that it usually takes to hone in the value), I became suspicious of my filament. As I loaded a new role of filament, I observed that the filament is deflecting as it extrudes. This leads to the filament getting stuck to the nozzel/heatblock. After a few rounds of extrusion, the weight of previously extruded filament will assist in straightening out the extrusion. However, in the video you can see the stream deflecting even under the weight of the previously extruded filament. I feel this may be the source of my issue. See attached video (IMG_5270).

I read that this deflection can be caused by bits of filament stuck to the nozzel/heatblock. My nozzel/heatblock have certainly had more debris on them in the past and I've never observed this issue as dramatically as I see it now. I did my best to rigorously clean the nozzle and heatblock. However, the issue still persists. I'm hoping the community can provide some insight into other potential causes. I'm thinking it could also be an issue with my nozzel. In any case, all thoughts are welcome. Thanks in advance. 

Posted : 14/01/2022 10:54 pm
Famed Member
RE: Filament Deflecting Upward on Extrusion

Deflecting filament is not caused by bits on the OUTSIDE of the nozzle, but by debris on the INSIDE.  You can clean the exterior as much as you want, it wont make that much difference.  Yes stuff on the outside does help other bits to stick so builds up but deflection is caused by disruption to the flow.  That is all inside.

Several things you can do.  You could use the needle and try and clear the nozzle out.  Personally I wouldnt recommend that.  The needle being steel can scratch the softer brass which is NOT what you want.  Anyway it usually dislodges bits and pushes them back upwards further in.  While they can then sometimes flow out as you extrude they are just as likely to get stuck again. 

A better solution and normal 'fix' is to perform a 'cold pull'.  Google the term and process.  There are many sets of instructions online. 
It sounds more complicated than it really is.  Once you have had a bit of practice its quite easy and doesn't take that long.  Much better for cleaning out the inside of a nozzle.  Made easier by using special cleaning filament but can be done with normal too.

Posted : 15/01/2022 12:26 am
Noble Member
RE: Filament Deflecting Upward on Extrusion

Everything neophyl said is correct (of course) but I don't think that video shows anything super unusual. Happens. I just use needle nose pliers to get the filament come out straight when loading. I wouldn't expect that to lead to layer adhesion issues. did you clean your sheet with hot water and dish washing soap? What's the results of first layer calibration?

Posted : 16/01/2022 2:22 am