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PETG Basics

hazmatt99
(@hazmatt99)
Trusted Member

Hello!

I know I've seen this information but I'm having trouble finding it. I'm about to start using PETG and I'm just wondering where do I start?

I've been using PLA exclusively and I know there's some differences with print settings like temp and cooling, I also know ABS has health and oder considerations and I wasnt sure if PETG had something similar.

So in short:

  1. What nozzle/bed temp range should I start with?
  2. What cooling percentage should I start with?
  3. Are there safety considerations that I should be aware of that are different from PLA?
  4. Are there any other quirks I should know about? Supports? Build plate adhesion?

Thank!

Quote
Topic starter Posted : 29/08/2021 1:22 pm
Luke
 Luke
(@lmf5000)
Expert Moderator

Hi Hazmat,

PETG is quite a well-behaved filament, not too different to PLA. It has low shrinkage (meaning it won't crack or warp itself off the build plate easily), low odour (although as always you should 3D-print in a well-ventilated room), a similar price as PLA, and an ever-growing choice of colours. The biggest advantages of PETG are that it's tougher than PLA (i.e. can handle impacts better without shattering) and can handle more temperature (PLA softens at 60°C, PETG starts at around 80°C). It's also easier to find transparent filaments in PETG than PLA.

Now, to answer your questions:

1. Nozzle and bed temperatures for all filaments are usually supplied by the manufacturers, written on the spools or boxes, but as a general rule if your printer has a regular PTFE-lined hotend you want to stay below 245°C to stop the PTFE tube from starting to thermally degrade and release toxic fumes in the vicinity of the printer. I personally print my PETG at 230°C. If you have an all-metal hotend (titanium liner instead of PTFE liner), then you can safely go up to 250°C. If in doubt, stick to 230-235°C.

For bed temperature, when I used plain glass I needed to go up to 80°C to get reliable adhesion. Nowadays with an Ultrabase (ceramic-textured glass) on each of my printers I only heat up to 70-75°C.

2. Zero cooling for the first three layers, then gradually ramp up to somewhere around 80-100% fan. More cooling won't hurt but you'll be adding noise and wear on the fan with little benefit. The beautiful thing about PETG is that its higher temperature resistance means that it overheats much less than PLA, so tall thin parts of the print still come out beautifully rather than wilting in the heat.

3. To the best of my research, the fumes from PETG have not been characterized to be more dangerous than those of PLA. Important disclaimer: This is subject to change as more research is conducted. Always print in a well-ventilated room with all windows and doors open and use fans to force printer fumes out of the room as rapidly as possible (or better yet use an enclosure with HEPA filtering). Don't trust printer fumes. There is copious data about how printing nylon releases caprolactam (which is nasty stuff), printing ABS releases styrene (also nasty stuff), printing PLA releases lactide (which isn't that nasty - as far as we know now), and I've yet to uncover some research indicating what exactly the fumes from PETG contain, but it's safe to say that whatever comes out of the printer will not be good for your health (even if studies haven't yet conclusively proven that PLA and PETG are bad) so take the usual precautions.

4. Printing-wise, PETG tends to stick to the nozzle more. Particularly if the filament is a little older (i.e. box has been opened longer than 6 months), it will then be dragged around the print, sometimes getting caught on parts of the print and being stretched by the nozzle into fine threads, and the threads will be melted back into a blob by the nozzle on the second pass - but this isn't something to worry about, it will just need more post-processing as it might leave visible blobs or threads on the finished print. Bed adhesion will be worse than PLA, but with the extra bed temperature you shouldn't have problems with it detaching mid-print.

Printing speed will have to be a bit lower due to the time needed to reach the higher melting temperature (I print at 60-70mm/s for PLA and 50-60mm/s for PETG).

One last thing to be wary of is that if you've been printing PLA and your nozzle is contaminated with PLA, the contamination will cause very poor layer adhesion in the PETG until it's all purged out. You'll get a print that looks great, but the first couple of layers will come apart in your hands with slight force. The rest of the print (other than the first few layers) will be solid and strong. To get around this issue, make sure you prime the nozzle really well when switching from PLA to PETG. You do this by heating up to operating temperature and then feeding a few centimeters (say 5cm) of filament into the nozzle to make sure you get rid of as much of the PLA residues as possible.

That about covers it, it's actually quite easy to print with and a lot more useful for functional prints that need to stand up to forces and loads during use because it keeps its shape better over time than PLA (PLA parts tend to relax and loosen over time, so things that are friction-fit when initially printed in PLA end up being loose and falling off within weeks; PETG keeps its original shape).

Hope this helps, let me know how it goes! 🙂

 

Regards,
Luke

ReplyQuote
Posted : 30/08/2021 9:06 pm
hazmatt99
(@hazmatt99)
Trusted Member

Hey Luke, Thanks for the info, good stuff!

I'll try this out soon.

 

On an unrelated note, I just put on my textured glass print bed because I was getting bed adhesion issues on my flexible ones with the textured stickers.  This made it worse, lol I'm assuming because I need to adjust temperatures or something. Maybe you also have some tips regarding using this kind of print bed? Going forward I'd like to stop using these flexible ones altogether because the surface warps so much I can almost never get the whole thing flat which has been really annoying for when I'm using up a wide area on the bed.

I have it leveled properly, I cleaned it, it just really didn't want to stick.

The print I'm trying to get working is made from PLA, it's essentially a long bar thin bar that doesn't have much surface area contact, a prime candidate for warping really. I normally set my bed temp at 50 and nozzle temp at 200, I'd really like to avoid using a brim or raft or something. Let me know if this is something you can help with!

ReplyQuote
Topic starter Posted : 01/09/2021 1:30 am
Luke
 Luke
(@lmf5000)
Expert Moderator

@hazmatt99

Hi Hazmat,

I know you mentioned that levelling is correct, but just to double-check, it's important that the filament should look flattened on top when printing, not rounded. Something like this -

image

If that's already correct, next thing to adjust is temperature. I use 60°C for PLA on my Ultrabases (textured glass), and I used to use 70°C for PLA on regular (smooth, shiny) glass. Glass is a poor conductor so the surface temperature will be 5-10°C lower than what the printer's temperature sensor (located on the underside of the metal plate of the heated bed) will be reading.

Aside from temperature, make sure you're printing slowly on the first layer. I use 50% of normal speed for the first layer on PLA. One more thing that will help is setting the print order to outside-in (outer perimeters first). This is because outer perimeters are printed at around half the speed of the inner perimeters, so starting with them gives an even slower first layer, increasing the chances of successful adhesion.

A hotter nozzle will help too, I use 210°C for PLA.

Lastly, long thing prints, especially if they're only around 4 perimeters wide (about 2mm) are very very likely to fail. Once you get about 20 layers high on such a thin print, the residual forces will pull up and detach the corners off the bed, and the rest of the print will soon follow.

One "hack" that will substitute for a raft or brim is to use little circle feet which you then cut off the final print with side cutters (add them at design stage or add a cylinder one layer high and about 10mm in diameter inside PrusaSlicer). The concept is like this -

image

In your case you'd place a circle on each end of the long object.

You might also be able to re-orient the object for better bed adhesion. If you want you can attach or link the stl and I will see if I can find a more optimal orientation for it.

Hope that helps! 🙂

Regards,
Luke

ReplyQuote
Posted : 01/09/2021 10:56 pm
hazmatt99
(@hazmatt99)
Trusted Member

Based on this it's entirely possible it's a design issue then. Latest setting I tested was 60C bed temp, 200C nozzle temp, 50mm/s print speed with initial layer print speed at 30. Essentially the only thing I changed from my normal so far was the bed temp, and somehow that turned to spaghetti faster.

Below is a picture of the first layer on textured glass to show print bed leveling, I think it's pretty good but maybe I'm wrong

image

And below here is a picture of what I printed with the flexible bed, bed was leveled the same way as the first one and the build actually didn't warp itself off the print bed but as you can see it's still warped. It stayed stuck but the compressive forces were enough to pull the build surface up with it.

image

Maybe your experience could help with my build, I'm essentially making a picture frame and going through a redesign right now. First version was printed all at once flat on the print bed and that worked fine, glued picture to the back. Second version I modified so that it could print stacked, great for printing multiple and then walking away but the quality wasn't the greatest, again glued picture to the back. This time I tried separating all 4 sides of the frame with the intention of attaching them together and wanted to have the picture slide in and out of a slit rather than being glued. Because of that slit I'm fairly limited with the print orientations I can use. I'm hoping I can get this working because the quality looks great on it (minus the warp) I can make many of them at once, and not gluing the picture means faster assembly. Maybe I need to make a sacrifice somewhere but I've attached the STL in case you have any ideas. Once I get some time I can play around with settings for the textured glass.

 

ReplyQuote
Topic starter Posted : 02/09/2021 5:44 pm
Luke
 Luke
(@lmf5000)
Expert Moderator

This is a bit of a challenge because of the long aspect ratio of the print. It's 240mm long but only 8mm wide, so the compressive forces will be quite significant.

Some suggestions to try:

1. Heat the bed above the glass transition temperature of the PLA (which is 60°C - so set the bed temp to 70°C). This keeps the bottom centimeter or so of the print above the temperature where it can develop significant internal stresses, so should reduce the banana-shaped warpage you're experiencing. As a disadvantage, this may increase elephant-foot warpage because hot plastic is less able to resist compressing under the weight of the print itself. It will also slightly lower the quality of the overhang in the lower part of the print (the 45° chamfers coming up from the plate).

2. Remove or reduce the chamfer at the bottom (red line) so the base grows (blue line added as an example) -

image

This gives you a wider area for the foot. Of course if the chamfer is an important aesthetic feature in the frame, this won't be an option, which leads us to the next idea -

3. Print in this orientation. This way you use the largest area of the model in contact with the bed, which should give best adhesion performance of any of the orientations -

image

Of course the major problem here is that the slot for the picture will very likely weld together at least partially (and there isn't really enough space to insert supports). Depending on the thickness of the picture you might be able to mechanically open up the slot. I've printed things like this and slid a craft knife through the slot to widen it enough to take a single sheet of A4 printer paper. You might need to use a dremel or such to expand the slot if a knife doesn't "cut" it (pardon the pun).

4. Use a breakaway raft (the one that gets added automatically by the slicer after enabling the feature). I use this for lithophanes. Unfortunately when you break off a raft it doesn't always leave a clean surface so this is the least favorable suggestion in terms of appearance, material usage, and post-processing work required.

---

For the first layer speed, try going even slower. I use 15mm/s with PETG and 25-30mm/s with PLA. As for the first layer height, to gauge it would require a view of the top of the first layer - or better yet, print some bed level squares (like these - https://www.thingiverse.com/thing:2789086 ) and measure their thickness with a micrometer or a caliper accurate to within 0.01mm. If your first layer height is 0.2mm, the squares should all have a height of 0.15-0.25mm (the closer to 0.2mm the better). Since you're using the whole length of the bed with such a long print, any concave or convex warpage of the bed will affect your first layer adhesion, and is not something you can compensate for using the normal bed levelling screws because the bed is literally curved, and the screws just re-orient the plane of the bed (it still remains curved). The way to compensate for that warpage would be to use automatic (firmware-based) bed levelling.

Do you have an automatic probe or use the manual matrix-levelling method, or do you only do mechanical levelling with the knobs under the bed, with no further autolevelling done after that?

 

Regards,
Luke

ReplyQuote
Posted : 03/09/2021 11:00 am
hazmatt99
(@hazmatt99)
Trusted Member

1. That's fine because the chamfers were put there to minimize the effects of elephant's foot at least enough so it doesn't create a sharp edge, also cut down on material BUT this is definitely something I'll try.

2. Shaving off the chamfer would be something worth trying if increasing the temp past the glass temp doesnt work, I could always shave down the opposite end too to balance it out, less print time less material

3. Slow clap for the pun. I've tried printing in this orientation with a much more shallow slit and even that welded together to the point where I couldn't put a picture in there, If I'm going to print in this orientation I'm just going to remove the slit and go back to gluing, less ideal but it would function at least. I'm selling these things and tbh I don't trust myself not to ruin the thing with a dremel lol.

4. Using a raft for me would be last resort for getting this particular design working, behind a brim, high cost of filament and time and like you said, lower quality surface finish, granted it's a surface that no-one really will be looking at but still. It's an option I just don't like it lol.

I do have autoleveling on my printer. Interestingly I follow the same process for bed leveling (which I got from here) for all my printers, and I can tell that the flexible print surface on some of them is the thing that's warped. The auto leveling sensor is the kind that detects the metal plate underneath the print surface. As an example, after manual leveling and setting all for corners a paper's width away from the nozzle, the autoleveling program will state that the right side of the plate is about 0.5mm lower than the rest and during printing it lowers the nozzle to compensate. When it goes to print and lower the nozzle in these parts, it goes way too close to the surface and drags along it. This is why I want to switch to glass, at least I don't have to worry much about glass warping, plus the sensor that comes with the glass plates I buy detects the surface height, not the metal plate. Hmmmmm maybe If I just use those sensors with the flexible beds.....wonder if that would work.

ANYWAY I'm going to try out some of the tips you gave me and see if I get spaghetti.

ReplyQuote
Topic starter Posted : 03/09/2021 11:32 am
Luke
 Luke
(@lmf5000)
Expert Moderator

Hi Hazmatt,

How did it go? I have some comments about the above -

1. For elephant foot minimization, you only need a tiny chamfer, something like 0.4mm. You could also use the "elephant foot compensation" feature in Cura and PrusaSlicer. I find that my printers don't make any significant elephant footing so I keep it at zero in my case.

2. Reducing the chamfer actually consumes more material because it cuts out less of the shape :). Though with 3D printing, you have to remember that you're actually only printing a hollow skin, not a solid object. So if for example you doubled the thickness of the frame, you would use somewhat less than double the material, because since it's not solid, all you'd be adding is a little bit of length to the skin on the sides, top and bottom, and a little bit of length to the infill. The bulk of the material use (the front and back) would remain unchanged.

Quick demo, here's the original -

image

8mm thick = 13.8g

here's double thickness - 

image

16mm thick = 21.82g. So double (200%) of the thickness but only 157% of the material use 🙂

3. Thanks 😆 . Maybe you can print a jig to guide the dremel and make it foolproof? I imagine something like the stencils they make for routers but designed to keep the dremel blade at the right depth in the slot. Or perhaps use a saw and a vice?

4. I dislike rafts too. There's no guarantee of success either, I've had prints detach from the raft on the edges while the center remains welded to the print and leaves white strain marks where the raft had to be forcefully pulled off.

The autolevelling is definitely hampering your efforts to print correctly. If the sensor is inductive/capacitive and is detecting the metal plate underneath, it won't compensate for variations in the thickness of the textured metal layer and any dirt you may have picked up between the textured surface and the metal bed. All it takes is a largish speck of dirt to lift the plate by 0.05mm and throw off that section of the plate. It's far more reliable to use a physical touch switch (mechanical or BLtouch for example) so I think you'd definitely see an improvement there.

Did you mechanically level the bed as well as you could before autolevelling? The less correction autolevel has to do, the better your printing results. Plus if you have a fade height set, your autolevel will taper down to zero by the time your print grows as tall as the fade height, so past that point you're relying exclusively on the quality of the mechanical levelling of your printer to keep the print from becoming lopsided ;). Diagram with a 10mm fade height to illustrate:

image

Looking forward to hearing your feedback 🙂

 

Regards,
Luke

ReplyQuote
Posted : 07/09/2021 11:06 pm
hazmatt99
(@hazmatt99)
Trusted Member

Hey dude!

Sorry it took so long I've been all over the place trying stuff and working etc.

So I tried it with increased bed temp at first and it worked great, if I had a brim and only printed 1 piece. But when I tested multiple pieces (which I'll definitely need to do) it's just really sketchy I'm at the point where I just want to move on with my life LOL. So I came up with a redesign to get rid of that gap in the middle of the thing that the paper is supposed to slide into and I changed the orientation to print on the side with the higher surface area. I'm going to try printing that tomorrow. I'm probably going to stick with that unless that also decides not to work.

I'm definitely going to keep all the tips you gave me in mind, like I might try the elephant's foot setting anyway. Learned alot trying to make this work but I want to get the important design updates pushed through first, namely being the larger size and splitting the pieces etc. I'll probably pick up the experimentation when I have the spare brainpower for it lol.

 

ReplyQuote
Topic starter Posted : 10/09/2021 2:09 am
Luke
 Luke
(@lmf5000)
Expert Moderator

That's great to hear :). A broader base with lower height is always better for adhesion, and further pluses are faster printing time and slightly less material usage.

---

When you're comfortable with 3D printing in the normal way, there are special features in the slicers that allow you to print multiple parts in one go rather than layer by layer. So instead of printing one layer of part 1, then one layer of part 2, then another layer of part 1 and so on, the printer prints all of part 1, then moves sideways and down, and prints all of part 2.

The advantages are greatly reduced print time and much less stringing because you eliminate all the travel between parts. The disadvantage is that you have to carefully measure your print head to make sure you don't hit any already-printed parts, and that the maximum height of the parts you can print this way is limited by the printer's gantry (about 30-50mm in most printers).

Once your brain has freed up some RAM let me know if this topic interests you and I will show you how to enable it in PrusaSlicer 🙂

 

Regards,
Luke

ReplyQuote
Posted : 10/09/2021 9:57 am
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