Blobs at every start and end of line



  • Hi guys,

    my new coreXY prints not so bad but I have a big blob issue, which I don't know like this from any other of my printers.

    First I thought it is an retraction issue but it is not as you will see in the following.

    I have a bowden setup and I tested it with the geared Titan extruder and with a non geared extruder. And I tested different hotends, filaments and temperatures as well. All this has no significant effect.

    To make sure my Titan extruder is fast enough I set pretty high values for E-speed, -acceleration and -jerk:
    E-acceleration = 9000 mm/s²
    E-jerk = 2400 mm/min
    E-max-speed = 9000 mm/min

    I can't here it loosing steps but I tried more conservative values as well with no big differences.

    I assumed, that the nozzle stays too long at a place, so that oozing has time to build the blobs. So I tested different XY accelerations. Non print moves are always set to 7000 mm/s². Print moves are usually set to 2500 mm/s². And here the results for different print move accelerations:

    0_1560428317579_acc.PNG

    As I said there is no retraction. The nozzle moves from the corner below right to the beginning of the line and instantly continues printing. I can not notice any delay. A high-speed camera would be interesting ...
    You can see, that higher accelerations are helpful. But even at 7000 mm/s² I have a little blob. And I don't want to accelerate that fast, as I will have more ringing then.

    So back to 2500 mm/s² and let's test pressure advance. I used the calibration pattern from the marlin firmware homepage and ended up with k = 0.35. But this value caused dramatic underextrusion. So I made a small test GCODE by hand. First I print a base and then I move from the corner below right to the middle and print a single line on it. Again no retraction activated:

    0_1560429316010_la.jpg

    The black part is the same GCODE printed on a widely similar machine but with marlin - no blob.
    As you can see, the blob disappears at k = 0.18 but even at k = 0.15 I have underextruded areas. So I'm afraid pressure advance is no solution for my problem.

    Now I can't think any further myself. The biggest difference between the printer of the black and grey part ist the electronics and the firmware. But I assume, that both translate the GCODE to the same movements without differences, right? I mean I can't imagine, that the duet includes any additional delays here!?

    I know I could set my Slicer (S3D) to force retraction at almost every travel move and layer change. But this makes the problem even worse, as the nozzle stays even longer at every start- and endpoint of each line. Plus I want to understand why I have this problem only with this printer. I hope so much for any advice.



  • Did you test if enabling retraction reduces the amount of blobs or do you just assume that the blobs will get worse? 😉
    Because I could imagine retracting could prevent that too much plastic gets out of the nozzle after the print move finished and before the nozzle takes off to another location.

    Best,
    Markus


  • administrators

    Pressure advance reduces the need for retraction; but with a Bowden extruder, you will always need some retraction to avoid blobs around travel moves.



  • @jorge i think (and sincerely hope) that your quoted speeds are mm/minute because 7,000 mm/sec is really knocking on. I've managed 300 mm/sec but only by using 5 extruders feeding into a mixing hot end with 5 melt chambers.

    Anyway, assuming you mean mm/sec then the blobs you describe can usually be tamed with pressure advance - it works well for me anyway. I'm not sure about the correlation between RepRap firmware and Marlin though. I don't think Marlin "K" is the same as RRF M572. Comparing your extruder settings with mine (I use Bondtech BMGs but the gearing and steps per mm are very similar to the E3D Titans) I have lower accelerations (3,000 mm/min compared to your 9,000), but higher "Jerk" (I use 3600 compared to your 2400). My maximum speed setting is lower but that's irrelevant because it will never reach 3600 mm/minute let alone 9,000.

    So higher extruder "jerk" will have an influence on pressure advance. Also, anything that alters the viscosity of the filament. I see that your corners have quite a bulge which might be an indication that the filament temperature is too high. That will cause blobs too. Have you tried lower temperatures and are you sure that your hot end thermistor has the correct values so that it is reading correctly?

    I'm not sure that I understand your comments about not using retraction. It is normal to have to retract filament just prior to non-print moves. Pressure advance reduces the amount of retraction required but it doesn't eliminate the need for it completely.

    It might be an idea to post the rest of your config.g file and the slicer settings you use.



  • Thank you guys so much for your help! According to your posts I did some more tests but without success yet.

    @change3d-gmbh said in Blobs at every start and end of line:

    Did you test if enabling retraction reduces the amount of blobs or do you just assume that the blobs will get worse?
    Because I could imagine retracting could prevent that too much plastic gets out of the nozzle after the print move finished and before the nozzle takes off to another location.

    Now I did 😉
    Actually the retraction shifts the problem a bit from the starting point to the ending point. So the blob in the end of a line becomes even worse as the nozzle stays there for the time of retraction. The starting point becomes a bit better but far away from good. I tested this also with different retraction distances. The longer I retract, the worse is the blob in the end of a line.

    @dc42 said in Blobs at every start and end of line:

    Pressure advance reduces the need for retraction; but with a Bowden extruder, you will always need some retraction to avoid blobs around travel moves.

    But the black part is printed with a bowden extruder and without retraction and pressure advance. I just don't get why both printers don't work the same way. 🤔

    @deckingman said in Blobs at every start and end of line:

    @jorge i think (and sincerely hope) that your quoted speeds are mm/minute because 7,000 mm/sec is really knocking on.

    Sorry, my fault. 😰

    @deckingman said in Blobs at every start and end of line:

    Anyway, assuming you mean mm/sec then the blobs you describe can usually be tamed with pressure advance - it works well for me anyway. I'm not sure about the correlation between RepRap firmware and Marlin though. I don't think Marlin "K" is the same as RRF M572. Comparing your extruder settings with mine (I use Bondtech BMGs but the gearing and steps per mm are very similar to the E3D Titans) I have lower accelerations (3,000 mm/min compared to your 9,000), but higher "Jerk" (I use 3600 compared to your 2400). My maximum speed setting is lower but that's irrelevant because it will never reach 3600 mm/minute let alone 9,000.
    So higher extruder "jerk" will have an influence on pressure advance. Also, anything that alters the viscosity of the filament. I see that your corners have quite a bulge which might be an indication that the filament temperature is too high. That will cause blobs too. Have you tried lower temperatures and are you sure that your hot end thermistor has the correct values so that it is reading correctly?

    I took over your acceleration and jerk and printed the test body once without pressure advance and once with k = 0.17 but the test body still looks the same.

    The bulge of the corners confuses me, too. I decreased the temperature until it nearly didn't extrude at all. And indeed the corners became a bit better but the blob is still there.

    @deckingman said in Blobs at every start and end of line:

    I'm not sure that I understand your comments about not using retraction. It is normal to have to retract filament just prior to non-print moves. Pressure advance reduces the amount of retraction required but it doesn't eliminate the need for it completely.

    From what I have gathered, retraction ist mostly important to avoid stringing and oozing when it comes to crossing open spaces. So if it's possible, I like to avoid retraction. So I usually set "Only retract when crossing open spaces" in Simplify3D and I deactivate "Force retraction between layers". With this settings a simple body like a block will be printed without any retraction. And for my other printers this works very well but the new one builds big blobs on every layer change.

    So my current aim is to get the new printer to print those simple bodys as good as my other printers without retraction and actually without pressure advance. Only afterwards I wanted to calibrate retraction. Do you agree or am I on the wrong track?

    @deckingman said in Blobs at every start and end of line:

    It might be an idea to post the rest of your config.g file and the slicer settings you use.

    sure ☺
    here the config.g, the S3D .fff profile and the S3D setting as images for those without S3D. Hope it is OK this way.
    download



  • OT: You left your wifi password in there?


  • administrators

    @jorge said in Blobs at every start and end of line:

    So my current aim is to get the new printer to print those simple bodys as good as my other printers without retraction and actually without pressure advance. Only afterwards I wanted to calibrate retraction. Do you agree or am I on the wrong track?

    IMO you are on the wrong track. Using a Bowden extruder, if you don't retract on layer change and you don't use pressure advance, you will get a blob unless the layer change happens very fast. Likewise if you don't retract before a travel move.

    Are you absolutely certain that you were not using any retraction or pressure advance on your other printer? Retraction may be done by the slicer generating direct retraction commands, or by the slicer generating high-level commands, or perhaps by the firmware.



  • @nightreaver said in Blobs at every start and end of line:

    OT: You left your wifi password in there?

    Thats an old password, so no worries 🙂
    But I just deleted ist though.

    @dc42 said in Blobs at every start and end of line:

    IMO you are on the wrong track. Using a Bowden extruder, if you don't retract on layer change and you don't use pressure advance, you will get a blob unless the layer change happens very fast. Likewise if you don't retract before a travel move.
    Are you absolutely certain that you were not using any retraction or pressure advance on your other printer? Retraction may be done by the slicer generating direct retraction commands, or by the slicer generating high-level commands, or perhaps by the firmware.

    Yes, pressure advance is deactivated for sure. And the GCODE was the same file. So there is no retraction in the GCODE. I double-checked it in a text editor. I have Marlin running on the other printer. I never heard, that it is doing any retraction or so by firmware?

    Here is one more test: I printed the same body again, once at the same speed as before (travel= 500mm/s, Infill = 60 mm/s, perimeter and testline = 45 mm/s), and once at 20% speed.
    0_1560700816732_IMG_20190616_172734.jpg

    It's interesting, that the infill of the faster one is underextruded compared to the slower one, even though 60 mm/s is not so fast. And obviously the blob almost disappeared at the slower one. I conclude that the hotend must be not slippy enough and there must rise a big pressure in the bowden. With this pressure even the shortest stop is enough to build this blob. Maybe the hotend of the other printer is kind of slippier, so that less pressure grows when printing at 60 mm/s? Maybe I should try one more hotend or just an other nozzle? What do you think?



  • This may be more trouble than you're willing to expend, but perhaps you could swap the Duet and the board running Marlin in order to eliminate hardware differences.


  • administrators

    Another thing you could try is installing firmware 2.03 and setting the jerk policy to 1 in the M566 command. That works more like Marlin does, by allowing jerk to be used where it isn't needed in theory, e.g. between a travel move and an extruding move.



  • I updated the firmware but unfortunately it makes no difference.
    Next I will test it with a simple 8 bit board with Marlin. I hope it makes no difference because I really like the duet and the Dibond housing is milled for it...


 

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