Fun with PETG

OK, so I’m fairly new to 3D printing, and have spent that time with PLA. I moved over to PETG to try something new. I printed the following object in PLA with no issues, with PETG, not so much.

I’m using eSun true white.
Temp of 239
Bed at 70
No cooling fan
Filament measures pretty true @ 3.0

The bottom layer and fill seemed to go just fine, but as it made its way to the to layer, well, take a look…

I"LL take any and all suggestions : )

Are you using Cura? It looks like your top layer might be too thin and it is getting too hot. I run my fan at 0 for the first layer and at 40% for layers 2 & up with PETG and it turns out great.

Yup, using Lulzbot Cura. Thanks for the hint. I’ll give it a try tonight. what temp do you use for the filament?

I found it depends a bit on layer height and infill settings/speed. I have a profile I’ve been working on for taller layers, 0.35mm. It was stripping the filament. I found that increasing the extruder temp by 10C, it stopped happening. For slower settings, 0.1mm, I find I can use a lower temp. I try to keep the temps down with PETG, as it’s stringy already. The strings are usually really easy to remove though, just rubbing the part by hand seems to get 90% of them.

Extruder - 245
Bed - 60
Bed removal temp - 45

For 0.35mm, I went up to 255.

I’m using Simplify3D, but generally I try to make the first layer about 0.4mm and the top layer a little thicker. If I’m using thick sides, I usually make the top/bottom about the same thickness.

For a large flat part like that, with low infill, the top layers need some thickness to level out.

I’m using eSun PETG, they spec it for 2.85mm and that’s about what I get. I don’t have the white though. Perhaps that’s different. Just making sure you got a good measurement for it in the slicer. I’ve been very happy with the transparent blue. I have a roll of black here I need to try.

I’m using the same temps as ttabbal (thanks for your help again), except my extruder at 240°C, at .2mm. My eSun PETG has been running between 2.86 and 2.90 so I set my filament diameter at 2.88 and that seems to work pretty well with a flow of 90%. Try the black, ttabbal, it is really nice!

The picture of the issue looks to me like either the hobbed bolt is slipping due to insufficient pressure on the idler or too much friction in the filament path. The result is that an insufficient amount of filament is getting to the extruder towards the end of the print.

I use PETG with good results on a TAZ 5 with 240C hot end and 60C bed. (Except last night when I had the same problem you ran into. I just cleared the filament path, checked the idler tension, and restarted the print.)

OK, good to know. I read somewhere here to keep the pressure on the hobbed bolt as low as possible to reduce the risk of bunching. I may have it too low, but the extruder does not indicate any issues until the top layers start to print.

Is there any rule of thumb for pressure or gapping for the tensioning screws?

Tension Jig

I’m having the same problem. On test prints, the print goes swimmingly at first.

The bottom layers and go down perfectly. The infill looks great with very minimal stringing on retracts.

Then when it comes time to put down the top solid layer, the whole thing immediately turns to crap. Without fail.

I’m varying the extruder temperature, cooling settings, extrusion multiplier, idler tension, you name it. No luck so far.

I know this is the opposite advice people give for PETG, but it might be worth a shot. My experience is that I get stringing with lower hotend temps and warmer ambient temperatures. So, when I’m printing in my garage and it’s the high 30s (F) in here, 248C hot end (80C bed), no fan, slower speeds (also make sure the combing is on in the expert panel in Cura). It comes out awesome when it’s frigid in here. If it’s in the 40s ambient temperature, quality deteriorates unless I use the fan at about 70% power (same other settings). A little underextrusion also helps.

I’ve noticed that stringing is less with larger layers – the things I’ve been making recently are parts for random equipment and so I’ve been doing .2 and .25mm layer heights. Very little stringing with my settings at these layer heights, but 0.1 brings the stringing and booger blobs back.

I’m thinking that when it warms up to the high 50s, I’ll switch back to ABS, which totally fails in my cold environment but I like it even better than PETG.

Anyway, a test piece with high equipment temps and lots of cooling might be worth a shot.

I’ve managed to make some progress.

With experimentation, I found a nozzle temperature of 250, combined with 100% cooling after the first layer looked the best out of all my other attempts. It still looked horrid when it came time to place the top solid layers, but it was the least horrid looking.

It then occurred to me that the only thing I hadn’t adjusted up to this point was my infill percentage. For PLA and ABS, I typically keep it at 20% fast honeycomb.

I use S3D, so I setup a print with four copies of the same hollow calibration pyramid model, each with a process set to use different infills percentages at 20, 40, 60, and 80 percent.

Again, the first layers and infill went pretty well. The 20% infill is the upper left square, and they increase going clockwise.

Here the top solid layers start to go down. The 20% square is really messed up to begin with.

I found that quality improved the more layers went down. I typically do four top layers, but for 20% that just isn’t enough with PETG.

The 40% square does better, but still has a visible blemish a couple mm in diameter. It’d probably do well at five layers. The 60% and 80% squares are pretty much identical.

So, there you go. More infill, more solid layers, or both.

Interesting results. What layer height are you using? I usually adjust the number of solid top and bottom layers to get about 1mm thickness at whatever layer height I’m using. That tends to give good results with PETG and HIPS. I haven’t done much with ABS or PLA though.

Hmm. Very interesting. I am experimenting with good settings, and I’ve gotten it pretty well in line. Here, you can see a print in progress. It is printing @ .2mm layer height and 40% fill. (2.88 diameter and 90% flow, I slowed down the top layer from 30mm/s to 20mm/s. Temps are 240 and 70 bed.)

But since I’m printing in solid white, I bet you guys haven’t seen this. Look at the black boogers. They are slightly raised bits of, what I’m assuming are, burnt bits of PETG. AS the top layer builds, it stops doing this, but A) it makes the piece ugly because you can see it through the upper layers, B) it certainly doesn’t make the nozzle happy if these get too big.

I cleaned out my extruder by doing a few cold pulls with PLA. Everything is clean. When I extrude material via the control panel, I get a clean stream of material.

These tend to accumulate during top layer, which lays down very thin and a bit stringly looking.

I run .2mm per layer. Having 1mm uppers and lowers is not a bad idea. I may make that my default in the future.

Does the PETG work well directly on the mini’s PEI bed, or is glue stick needed?

In particular, I’m wondering not only if it sticks “well enough” to PEI, but if there is any problem with it sticking “too well”.

I find PETG sticks just about right to the PEI bed on my Mini. I don’t see any need for bed treatments like glue sticks. Removing at about 45C, rather than letting the bed cool all the way seems to help.

I’ve found that with 240 deg. extrude and 70 deg base, larger objects, those greater than 4x4" with completely flat bases stick rather well, and even after cooling to 55, take a bit of effort to pry up. That includes having the fan off for the first few layers.

On the other hand, when creating narrow pieces; 1X10", I do have an issue with warping which I have not worked out yet. Maybe a hotter bed.