Filament jams on 2nd to last layer
 

Filament jams on 2nd to last layer  

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scott-7
(@scott-7)
Active Member

We are using Prusa Slicer 2.1.1 with our Two Trees Sapphire Core XY machine. When we received our new MK3S we were hopeful that we could use the Prusa Slicer for both printers but we have a problem we are unable to resolve. The MK3S is working great and we decided to upgrade the Sapphire hot end to an E3D V5 using a boden style set-up. We dialed in the settings fairly easy using a 0.5 nozzle and printing a 1 inch test cube. The print quality was looking absolutely amazing until the 2nd to the last layer. About half way thru the 2nd to last layer the filament stops flowing, the extruder starts clicking and the print fails. We have tried adjusting every possible slicer setting but without success. We tried printing a 1/2 inch high test cube but again, the same result.

This may or may not be related but the reason we decided to upgrade the hot end is almost the exact opposite of the problem described above. Printing a similar test cube, we would get a flawless print up to the final layers but instead of a filament jam, we were getting over extrusion on the 3 top layers.

A friend suggested that we look at the G code to see if for example the temperature was changing during the final layers but we do not have any experience yet with G code. The temperature listed on the LCD does not fluctuate at or near the time of the failures. 

Is it possible to share G Code files on the forum? 

Thank you in advance for any suggestions you may have!!

Scott 

Posted : 02/04/2020 8:52 pm
Neophyl
(@neophyl)
Noble Member

You have to zip up files to post the.

By all means post your gcode but could you also save your projects as a 3mf (save project as from the file menu) and zip and post that too.  3mf files are REALLY useful for debugging as they contain not only the model but all the settings you are using too.  They allow people to spot things you otherwise wouldnt.  For example recently someone was having trouble with the fan not coming on after the first 2 layers, turned out they had accidentally changed the gcode flavour to makerware instead of marlin so the fan commands were wrong.

This post was modified 8 months ago by Neophyl
Posted : 02/04/2020 10:49 pm
scott-7
(@scott-7)
Active Member

Thank you for that reply! Here is my sliced test cube.

Test Cube

Posted : 02/04/2020 11:20 pm
scott-7
(@scott-7)
Active Member

This is the Gcode file zipped up.

Test Cube

Posted : 02/04/2020 11:22 pm
Neophyl
(@neophyl)
Noble Member

Ok had a look at the project.  There's a few things I'd try to see if they make a difference.  

The clicking indicates that the drive gear cant extrude the material for some reason, obviously not a clog otherwise it would impact later printing but it sounds like the back pressure increases which is leading to your issue.  So the question that leads to is whats causing the extra back pressure at that point in printing.

Usually printing narrower than the nozzle isnt a good idea so your Solid Infill and Solid Top infill being set to 80% is looking problematic.  As its having the issue when its getting to the solid infill/top solid infill part of printing thats one thing I'd change right there.  If you look at the preview you will see your extrusion thickness is the ~0.70, changing to 0.55mm for your perimeters and infill up to layer 40 which from your pics looks like it prints ok (as its the top layer over the infill)  and then at your problematic layer changes to approx 0.236mm  which prints for a little while and then backs up.  I know you have layers 2 and 3 printing with that thickness 0.236mm too but when those are printed the fan is turned off (fan off for first 3 layers) which means the extruder is probably a bit hotter.  You do realise that when you use % values for those settings it is NOT based on nozzle size but its a % based on layer height.  I know thats weird but its the way Sli3er has always been.  I suggest you set 0.4 explicitly in there and try it or better yet set them at 0.5 to match your nozzle.  Slice it, look at the preview and select view width to see exactly what I mean.

Secondly I'm not familiar with the brand of PLA you are using but those temps seem on the low side, even for PLA.  Increasing them would allow the material to flow easier which would reduce back pressure overall.  

Thirdly we come to the cooling fan.  As mentioned when printing layers 1-3 the fan is off so temperature should be quite stable and we have the heat from the bed to help too.  During perimeter and infill printing the model has 'open spaces' but when it gets to the narrow layers for your top the fan will be blowing back up off the flat surface which will cool things down further and could impact things.

Id try both the extrusion width to 0.5 first and then upping the temp slightly and see if that helps.  

Posted : 03/04/2020 7:55 am
scott-7
(@scott-7)
Active Member

Hello my friend! Thank you very much for helping me with this. Today I had a chance to try some of your suggestions. I was confused about the 80% for the extrusion width of the solid infill and solid top. Also, thank you for mentioning the preview by feature. That is something i was not aware of either. Playing around with the advanced print settings regarding the extrusion width did correct the building of back pressure to the extruder as you suspected.

As you might have guessed, I have been playing around with so many of the settings. The extruder is no longer clicking but my print quality was not too great. I decided to take all my setting back to the defaults and I also decided to recalibrate the extruder step value just to be sure.

I know the temperature settings look low but someone told me that black typically prints at lower temperatures. I will experiment with that as the days in quarantine go on.

Everything  is looking very promising at this point. I just pulled my second test cube of the printer and it is nearly perfect. I only had to make two minor changes to the extrusion widths. I attached a snip so you can see what i did.

I really appreciate your time and suggestions!

Posted : 05/04/2020 10:45 pm
Neophyl
(@neophyl)
Noble Member

One bit of advice, don't use widths determined by %.  They don't work like you expect.  With a 0.4mm nozzle configured you would expect that 100% would be an extrusion width of 0.4mm.  Its not.  If your layer height is 0.2mm then with 100% your extrusion width is 0.2mm.  If your layer height was 0.15mm then you guessed it the extrusion width would be 0.15mm.  So you setting 190% with I'm guessing a 0.2mm layer height is almost 0.4mm.
You are far better off setting actual values in there or leaving them as 0 which applies the values mentioned in the tooltips, which is based off the nozzle size specified in the machine setup.

Posted : 06/04/2020 7:23 am
Sembazuru
(@sembazuru)
Prominent Member

If you determine that your issue is (at least partly) related to airflow from the part cooling fan exacerbating a marginal situation, you might want to consider getting a silicon sock for your new E3D hotend. They help diminish the effect of air blowing across your heater block from the part cooling fan.

See my (limited) designs on:
PrusaPrinters - https://www.prusaprinters.org/social/1448-sembazuru/prints
Thingiverse - https://www.thingiverse.com/Sembazuru/designs...
Posted : 07/04/2020 10:15 pm
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