PETG - do you hate or love it? And what are your optimal settings to limit stringing on an ultimaker 2+?

[Alex_RDPRobotics 0]

Hello All,

 

As I said in my most recent post, happy holidays, I hope you and your families are doing well wherever you are. I have an ultimaker 2+ and have recently been branching out in materials. I have been working with PETG for some time now, though I still prefer Alloy 910 for many of my prints due to its toughness, though the moisture absorption properties of nylon are a bit of a pain to deal with at times. I have several spools of PETG I had to purchase for a consulting project and have been gradually going through them for a development project of my own. I get pretty good output if I use, for a 0.4mm nozzle 0.15mm layer heights on PETG. But once one crosses to 0.2mm layer heights the quality becomes absolutely terrible - stringing, blobs, zits, etc. I have done quite a bit of tuning and made some improvement but wonder if it's simply a PETG issue - keep the layer heights only up to 0.15mm for a 0.4mm nozzle. I've gone through many temperature and retraction tuning settings, but when there are many retract type flow start/stop movements for a part the quality seems to really drop on 0.15mm and for 0.2 becomes aweful. Is there anybody who has really dialed this in such that, regardless of the number of retracts (assuming reasonableness of course) you are satisfied with a 0.2mm layer height? Any insights on doing so?

 

I'm not sure if I really like or dislike PETG because it's a bit of a pain for certain parts and comes out beautifully for others. Its temperature tolerance is great - I've used it in places where PLA lost its shape holding a warm thermal camera. It can be strong but is definitely more brittle than alloy 910. Doesn't warp, but this stringing and blobs/zits issue is a not so fun aspect. I have dry filament and gone through what I have read typically on retraction and calibration for this material, but maybe I'm missing something obvious.

 

Best,

Alex

[GregValiant 1,354]

I've printed quite a bit of PETG on my Ender.  I found that printing as cool as I can get away with and at 35mm/sec is a good thing.  I'll print PLA at up to 150 but PETG is a lot better when put down slow.

I typically print PETG at 225° with the bed at 80°.  A lot of models require elephant ears to keep them from warping off the bed.

I also raise my retraction distance to 6.5 (PLA at 5.5) and set the retract/prime speeds to 25.

 

A lot of the stringing can happen because PETG tends to collect on the nozzle a lot more than PLA.  When that blob on the outside of the nozzle gets to a certain size it slides down, touches the print, and then is like a second extruder that just makes a mess.  

 

[Alex_RDPRobotics 0]

Hi GregValiant, thank you for your response, that makes sense. I am finding that I get underextrusion if I reduce temperature with the ultimaker, so I have not been able to drop down to 225, using polymaker PETG. I have noted that there are some nozzles with extended tips so as to put more distance between the body of the nozzle and the print but have not seriously explored those. Perhaps I should look more carefully at its tendency to underextrude and try harder to reduce the nozzle temp.

[GregValiant 1,354]

I forgot to mention that I print PETG at 105% to 107% flow.  It is the same diameter as my PLA so it is likely a material property thing.  Could be my cooler print temp as well.  I have say the quality and finish of the prints is excellent, they just take longer.

[Alex_RDPRobotics 0]

Yes there is often a tradeoff of speed vs quality bu it's not a linear slope is it? Thank you for that input I'll experiment.

[geert_2 558]

I also print PET (or PETG, I don't know) at the lower edge of its temp range, sometimes below its recommended range, and at far lower speeds than PLA.

 

When molten, PLA becomes sort of yoghurt and flows easily, but PET rather stays like soft, rubbery chewing gum, it does not like to flow well. PLA bridges well, but PET tends to snap and fold back onto itself, so instead of a nice bridge I often get a sort of "grapes" accumulating on the edges.

 

And as said before, it tends to accumulate on the nozzle, causing a thick blob that slowly sags onto the print every so many minutes. The blob gets brown due to decomposing, if the temp is too high.

 

I use no cooling fan, and have no problems with warping.

 

I find PET is best for things that need a little bit of flexibility, like snap-fit mechanisms. But it is not stronger than PLA, only more flexible, and has a bit less creep under load. And it can go up to 70°C where PLA can only go to 50°C, and under load even not that. So PET is suitable for use in a car, PLA not (don't ask how I know). When printing without cooling fan, layer adhesion is good, I have no separation.

 

Clarity in transparent PET improves a lot when printing slow and in thin layers, indicating that there is far less air entrapped between the extruded sausages.

 

All bad effects are minimised when printing cooler, slower, and in thinner layers.

 

A few examples:

 

Ruler is in cm an mm:

 

 

PET can be chemically smoothed with dichloromethane easier than PLA, and it does not seem to dry out in het months after treatment, contrary to PLA that tends to develop microcracks. Both parts are identical, but one is smoothed to remove layer lines: much more hygienic for use in hospitals, easier to clean.

 

Transparent PET printed at different speeds and layer thicknesses: blocks are 20x10x10mm. Printed at 0.4, 0.3, 0.2, 0.1 and 0.06mm layers, top row at 50mm/s, bottom row at 10mm/s if I remember well. The yellowish discoloration is from sitting long in the nozzle at very slow speeds: it begins to decompose. Temp mostly is 215°C, except the thickest layers at 225°C, and the thinnest at 200 or 205°C. The watermark with my name is sitting halfway inside the block, it's hollow text, and only readable at low speeds and thin layers.