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Trouble with stringing + not smooth surface PET


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Posted · Trouble with stringing + not smooth surface PET

Hi everyone,


I have just started to print with PET filament and I observed some defaults on my first attempt. I have an UM3. I set the printing temperature on 235°C, the bed temp on 50°C, and the printing speed on 30 mm/s. Overall, I am satisfied with the result but I observed some stringing and some holes (very thin) on the surface. The odd thing is that I printed two identical parts at the same time, and only one of them has those defaults. Retraction was enabled (on Cura, I kept the defaults settings).

I would really appreciate if you had any thoughts on the fact that it is not symetrical, and how I could get a better printing result, or if it is normal ?

Thank you 



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    Posted · Trouble with stringing + not smooth surface PET

    The weird "worms" or "insect-antennas" that you see, probably come from the nozzle leaking while traveling through air. Upon reaching the other wall, the leaked blob is deposited on the side of that wall. Then next time, the blob is deposited on the already existing blob. So you get a sort of worm.


    Brown spots are usually molten material that accumulates on the outside of the nozzle, and then burns a little bit and discolors. Then it sags down and is deposited somewhere on the print in a big brown blob. At least, that is what happens in my printer when printing PET.


    The holes, I don't know. Maybe material that has leaked away during traveling through air, so there is not enough on the first moments of printing again? Or too high retraction settings? But this is just guessing... Try a small test piece, and carefully watch what happens.


    In my prints, I can reduce the first two phenomena by printing slow and cool, near the bottom of the range. Typically 220...225°C and 25...30mm/s, but I can not totally eliminate it. But of course, it could be different with other brands and colors of PET, and other printers. I have UM2, and the PET is from the brand ICE.


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    Posted · Trouble with stringing + not smooth surface PET

    Thank you for your answers.

    @geert_2, I've tried to print my parts an other time and I watched the printing process more closely. I observed exactly what you describe (about the "worms" thing and the brown spot), some filament is extruded ("leaks) while the printcore travels. Also I print with two materials at the same time (PET, printcore 1, for the part and PVA, printcore 2, for the support), and it worsen the leakage problem. The moment when the support part is printed (PVA) gives more time for the PET to leak from the first printcore. 

    I will try to slow and cool my next print, and I also use the PET filament from ICE. Are you satisfied by this filament by the way ?


    @P3D, thanks for the tip, I will test that

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    Posted · Trouble with stringing + not smooth surface PET
    3 hours ago, Cecile said:


    I will try to slow and cool my next print, and I also use the PET filament from ICE. Are you satisfied by this filament by the way ?



    I haven't printed with any other PET, so I can't really compare with any other PETs. It appears similar to NGEN, except that NGEN is better in bridging gaps. But strength and flexibility are similar.


    Compared to PLA:

    - For PLA, I use my "salt method" for bonding to the glass (=wipe the glass with a tissue moistend with salt water, that is all). But this does not really work for PET if I need a lot of cooling, so I need to use another method.

    - When using dilluted wood glue as bonding method, this PET bonds very well, but tends to tear pieces of glass out of the glass plate. Already while cooling, even before I start pulling it off...

    - So I usually print it on bare glass, which works well, but then I need to reduce cooling to avoid edges lifting on big models.

    - Without cooling, it is difficult to bridge gaps: the filament tends to curl up in a ball on the nozzle, instead of pulling a nice string to bridge the gap. So top layers of hollow models are difficult to close.

    - It tends to create a glossy residu in the nozzle, sort of hard "varnish", which is hard to clean. While PLA tends to create a black carbon layer in the nozzle, which comes off easier.

    - It has a nice glossy finish.

    - Its transparancy (frosted glass look) is good for embedding logos and text as watermarks in the model.

    - Layer bonding is good, even at the lower edge of its temp range. I usually print at 220...225°C, 25...30mm/s.

    - It is more flexible than PLA, so it works a lot better for snap-fit lockings, key rings, and similar things that need to flex a bit. In PLA they break after a few months as it gets harder and brittle. Not so in this PET.

    - PET models survive in a car in the sun, contrary to PLA.

    - Strength is quite similar to PLA and NGEN, not great, not bad.

    - Bottom layer towards the glass is almost perfectly flat, high gloss, and reflects like glass.

    - Seems to have a bit less creep when under continuous load than PLA, but still does deform, like almost all plastics.


    So in general I think it is okay, not great but not bad either. I use it mainly for models that need a higher temperature resistance, that need some flexibility, or that need some transparancy. But the majority of models I print in PLA or PLA/PHA. If it wouldn't leave the hard residu in the nozzle, and if it would close gaps better, I would use it more.


    These items are in ICE PET (all text are hollows totally inside the model, text characters are 3.5mm caps height x 2mm wide x 1mm deep, sitting 0.5mm below the surface):



    Actually, the "top side" is the bottom side while printing: this side is on the glass.





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    Posted · Trouble with stringing + not smooth surface PET

    I think PETG materials are very different in their behavior of how well they stick to the bed. I have tested CPE and colorfabb XT, but both don't stick to the glass bed with just glue. Also, blue tape is not working every time, sometimes it sticks good, sometimes not and I always wipe the tape with alcohol to get rid of the wax layer on it.


    I have good experiences with 3DLac and also with Dimafx. 3DLac is like hairspray and it just works and can be used multiple times. PETG sticks very good to it and can be removed easily with a spatula.


    Dimafix is a little bit different because you have (or should) reapply it after every print, because the area where the model sticks to the bed has no more Dimafix layer after removal. But the spray is great, it sticks very very well during the print when the bed is heated and after cooling down, the part comes of itself without any force or spatula. 


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