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Printing PET: less strings, hairs, blobs with lower traveling speed?

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Okay, so this is going to be heresy. :)

We all know the rule: to minimise strings and so, you have to increase the nozzle traveling speed. Faster traveling tends to break the strings, and it doesn't give the nozzle enough time to leak.

But now while trying a new PET material (new for me), I found out that this does not necessarily work well always.

At my normal printing speeds and temps (good quality: 20mm/s, 210°C; standard quality: 50mm/s, 225°C; material PET, ICE brand), I got little hairs, short strings and blobs in the prints. The blobs occured during traveling fast over already printed material, when the nozzle left behind sort of little "morse code" pieces. This is due to the nozzle not retracting when traveling over printed parts. Then, when printing the next layer, the nozzle would hit these morse-code blobs and they would accumulate on the outside of the nozzle. Then they would melt, get brown, sag down towards the print, and cause strings and hairs, and bigger blobs, all left behind on the prints.

It seems that if the nozzle travels too fast, its leaks do not have time to melt and fuse with earlier printed material. So they stay on top as separate little pieces, the "morse-code".

Then I got the idea to reduce traveling speed to 20mm/s, same as printing speed. Result: far less build-up of material on the nozzle, far less blobs, strings, hairs. And a visibly cleaner print.

At least, as long as there are no overhangs or bridges to print. This material does not like bridges: it is rather sticky and rubbery when molten, and tends to glue to the nozzle instead of pulling the bridge-line (contrary to molten PLA which is more creamy). Thus bridges and big overhangs still cause blobs and hairs, although less than before.

Disadvantage: while traveling over printed parts of the model, the nozzle leaves behind a line. It did so before too (although it was rather a morse-code line, usually), but now the line is a bit thicker. But now it is equally glossy as the rest of the print, while before it was matte when the rest was glossy.

I have only done a few small test prints, and only with PET (ICE brand), sliced with Cura 14.09. So I don't know if it would work for other materials, or other brands of PET, or other Cura-versions.

Anyway, those of you who have problems with blobs and hairs in their prints, might want to experiment further. Let us know your results.

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Also just used some ICE filaments PET and in a way nice to see someone having similar issues as me although I've not yet tried reducing the travel speed so will give that a go.

I'm not finding the material very strong though, was printing at 225°C and 25mm/sec. Have you had any further success since you posted the above?



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The ICE PET is more flexible than PLA, so in applications where it has to flex a bit, such as keyrings or snap-fit clips, it works better and has a longer life.

But thin plates or structures do sometimes fracture indeed. So I don't think it is stronger than PLA, only more flexible. And it is transparant, which may be usefull in some cases, for example to make watermarks, rulers or logos totally inside the model. So I use it mainly for these purposes. In other cases the transparancy may be a disadvantage.

I also printed around the same temp and speed: 25 à 30mm/s and 220 à 230°C. Printing a bit hotter and without fan improves strength, and improves transparancy, but not very much.

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