Can't get PLA to stick

Discussion in 'Calibration, Help, and Troubleshooting' started by sebastiaan, Apr 4, 2016.

  1. sebastiaan

    sebastiaan Member

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    I'm in need of some help to get PLA to stick to the bed of my dual. I've tried bare glass, painters masking tape and hairspray. None of these seem to get the PLA to stick to the bed. Instead the PLA curls and sticks to the nozzle making one big blob of molten PLA.

    The bed is leveled using the level bed feature from the menu and the PLA is put on the glass in a nice wide and thin layer. The PLA curls up a bit at the point where it's first put on the bed and then stays nice and steady on the bed untill the nozzle makes a turn and pulls apparently then pulls on the PLA a bit. The rest will come loose and mess up the print.

    The PLA used is Colorfabb PLA. I'm able to print with this and the same masking tape on a Prusa i3 just fine.

    I've got the fans turned off, the bed heated to 60 degrees and the extruder at 210. Turning down the extruder to 190 doesn't help.

    I've tried different settings for the first layer width and height but can't find a setting that works.
     
  2. Steven Burns

    Steven Burns Well-Known Member

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    Can you post a picture of what the first layer or two looks like? It may help in troubleshooting the issue.
     
  3. PsyVision

    PsyVision Moderator
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    Sounds like the nozzle is too high?
     
  4. sebastiaan

    sebastiaan Member

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    A piece of paper (A4 80 grams) can barely move between the bed and the nozzle. Does the nozzle need to be directly on the bed?

    I've uploaded a video of a print of benchy.


    I think it's over extruding and there's also a lot of build-up of pressure in the nozzle when the print heats up. Lot's of PLA starts flowing without any extrusion running. That causes PLA junk to build everywhere and then drag on the print.

    I tried an extra with less extrusion and wiping the nozzle in the dock. Some of the PLA still sticks to the nozzle and isn't wiped off as you can see in the pictures.


     
  5. Old_Tafr

    Old_Tafr Well-Known Member

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    I had similar problems though not as bad, just a blob of PLA on the nozzle. In my case and possibly yours I need the commands to wipe the nozzle immediately before the print starts. This isn't suggested anywhere that I can see, but could be added to Edit Process Settings -- scripts -- starting scripts in s3d. When I can find the command to wipe the nozzles (probably in the bency gcode file) then I will add it.

    If anyone knows where to correctly add the script and the commands then it may help both Sebastiaan and myself.

    PS I also found and don't have the final answer to the fact that in Octoprint the nozzle temp is set correctly but NOT the bed temp. If I don't set the bed temp manually the print starts with just the nozzle up to temp. A long shot but check in Octoprint and on the printer display to see what the bed temp is.
     
  6. Karel

    Karel Member

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    If you live not too far away from me, we could have a look together what's the issue.
    On my BigBox PLA is behaving 'normally' :)
     
  7. Rob Heinzonly

    Rob Heinzonly Well-Known Member

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    You need some adhesive on the bed, even PLA won't stick to the bed that easy. Use an Uhu stick, or hairspray to make the filament stick to your bed. With my old Prusa I used Kapton tape, but now I'm into the Uhu stick. Works marvelous.
     
  8. PsyVision

    PsyVision Moderator
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    I can get PLA to stick on the glass direct but do prefer some hairspray.

    It's hard to tell as your video isn't really that close to the nozzle. It looks as though it doesnt really squish the filament down at all so is still too high. If it was over extruding then I think it would be sticking.
     
  9. sebastiaan

    sebastiaan Member

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    Problem was that the printer was extruding too much PLA and bare glass isn't easy to print on. After more calibration of the extrusion and tweaking the extrusion multiplier and first layer height and width I got the PLA to stick.

    Settings that work for me with Colorfabb PLA are 0.9 extrusion multiplier, 100% first layer height and 125% first layer width with the bed at 60 degrees C and extruder at 190 degrees C.

    The glass needs to be really clean to get it to stick well. With blue paper masking tape I get much better results.
     
  10. Old_Tafr

    Old_Tafr Well-Known Member

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    Try moving the print cooling fans much lower, regardless of what else worked.

    Fans too high does seem to cause different and even inconsistent problems but the effect is to cool the nozzles and the pla. If you look where the air is coming from, from these two fans (to the left and right of the nozzles) there is a sort of spout like duct that shields the nozzle from the blast. I had mine too high and the cooling of the nozzles cause a "thermal runaway" (downwards and very obvious on the OctoPrint temp graph) error with the Rumba stopping (I hesitate to say crashing as have been told off :) and told that it is a designed feature that stops the Rumba......... but as it's out of action and there is no way to fix it you have to power the BB off and on)

    I think the combination of the fans being too high and the fans being on full power at the very first level does not help the filament stick, it obviously has to be melted to stick, so if you almost instantly cool both the nozzle AND the plastic with the print cooling fan blowing like mad then the first layer warps. I guess the heated bed should help but at 60oC for PLA it's hardly warm.

    I found that as well as moving the fans down to within a few mm of the nozzles I also had to adjust the fan speed for the first few layers in s3d at say 1 = 0%, 2 = 0%, 3 = 20% 4 = 30% and so on finishing at 6 = 60% ish this was for a relatively small printed part and on a raft.

    Ticking the "blip" fans box heps start them as at low % power then just oscillate......... putting a small dab of white paint or tippex on the fans helps show when they are moving or just dithering about.

    The lowered fans stopped the thermal runaway and the lower fan speed stopped the pla from cooling too soon and curling up. If the nozzles are hotter then the wipe immediately before you start printing should remove more of the PLA so there is less to cool and stick.

    I cleaned the glass bed quite vigorously with a scotch brite scouring pad but no liquid.
     
  11. Alex9779

    Alex9779 Moderator
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    Read this, do not use the blip option in S3D. It is not needed, it could produce blobs...

    EDIT: I did test with my dual fans and mine are running properly at 13%.
    Blipping does not help to reduce that, not in the firmware and not with the S3D option.
    Even let the fans run at 100% until they are at full speed (+5 seconds) and then turn down to <13% they will stop after >15secs.
    So IMHO the blip option in the firmware is not needed too for the side blow fans we have one the BigBox.
    Maybe someone else can check this? Just set the fans to 100%, let them run then turn them down and note the percentage when they stop. Then try to set the lowest percentage they kept running on the previous test but now when they are stopped. This time the firmware blip should step in, you won't notice but it does, and they should run.
    I tested with a modified firmware with that option disabled and they still ran at 13% even with no blip. 12% they did not run...
     

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