What causes bubbles in extruded filament?

  • I've noticed this on almost ever print I've ever had. On the initial first line that clears the extruder nozzle tiny little bubbles/craters seem to form on the line. While I don't think these are causing any issue with my prints I'm curious to know the reason why they form at all.

    Is this due to water absorption in my filament that turns to steam, which then bursts through the molten plastic? Is it due to air bubbles in the filament that are cause by the manufacturing process of the filament? Or is this more an indication that my nozzle is damaged or clogged in some way?

    Bubbles in extrusion

    This image was made using ABS plastic and a heated build plate. I've noticed these same 'bubbles' appearing using PLA, and Nylon.

    Edit: Nozzle temperature 240°C, build plate temperature 150°C, Nozzle diameter 0.4 mm, filament diameter (measured 1.75 mm) retraction distance 1.7 mm. Using the Makerbot Desktop Slicer.

    The first line that my printer extrudes, where I'm seeing these 'bubbles' is a nearly full line. Makerbot starts from the right side of the image, extruding to the left.

    Single line extrusion on printer bed

    Please provide the head temperatures, feed rates, nozzle diam, etc. What I see in the picture looks more like a startup problem of the nozzle feed "chamber" not being completely filled yet. Try preheating the head and manually forcing the filament in so that a couple inches are extruded before initiating the print code.

    The last 10 prints i've done seem to be looking like the 'bubbles' occur more often right at the beginning of the print/ first line. Would this be more indicative of a retraction setting issue do you think?

  • StarWind0

    StarWind0 Correct answer

    6 years ago

    Oh yeah, that's simple. You are printing too hot and are literally boiling the plastic. Else you have water. However if it was water you would hear Crackling as it printed. If it is too hot you will not hear nearly as much. I am 87.341% sure you are printing too hot.

    Looking at your printing temps you are without a doubt printing too hot.

    From this link on 3d hubs.

    PLA (Only on Replicator 2) Print temp: 210°C (at 100m/s) Notes: heated
    bed optional between 40 and 60°C

    ABS (Only on Replicator 2X) Print
    temp: 230°C (at 100m/s) Notes: heated bed at 110°C

    I'll give it a try at lower temps, (was at 240C for ABS). I've been raising the temp to try and improve the top layer/last layer thinking that I was running a bit cold. Might have to open another question on that instead now :)

    In those cases you want to lower your solid infill speed. That way it goes slower on those layers and adheres better. Speed and Temp are always in opposition.

    Very useful information. This is what was causing my bubbles so if the feedrateis too slow it will get too hot and be boiling.

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Content dated before 7/24/2021 11:53 AM