PETG weaker than PLA.
Hello,
I'm quite new to 3D printing world, but since I've started dreaming about Prusa printer, I aimed for the PETG printing. After purchase and assembly I started pirnting parts for project to my University. I guess, that my 3D modeling skills (material managment) are poor, because I ran out of default silver PLA shipped with printer. Lucky for me (I was a little in hurry) I got a spool of PETG, and encouraged by tales of its mechanical properties, loaded new filament, and printed said parts (around 26h total). I had a little issues with adhesion, so I turned up temps (245 first layer, 255 rest - I print in basement, temperatures are quite low) and moved on. At the morning I picked up one part and tested if it will be stronger. It was not. Part, that was strong enough in PLA versions, broke alongside layers (luckily, people invented hot glue). I considered it bad luck, and after some research blamed humidity of the place.
But, today I received new spool of PET (Fiberology Easy) and immediately after unpacking I took it to print Y axis linear bearing holders. I gave the same settings as for previous test print with PLA (excluding temps and material ofc), that means 100% rectilinear infill (I know, that more perimeters are more efficient, but I wanted to compare materials). Total print time - 1h20m. And part is a lot more flexible than PLA one, if I would flex it more it would snap across layers - thing that took me considerable amount of force applied to PLA equivalent (I kinda had to break it). This time humidity shouldn't play a role, spool went directly from vacuum packaging to warmed-up printer.
What can I do wrong?
Best Answer by Chocki:
Not all PETG is the same, different manufacturers use slightly different blends which will affect the final rigidity, strength etc.
For instance my experience, SUNLU White can be quite stiff since white will have quite a bit of titanium dioxide added to get the whiteness, this acts as a filler which will help stiffen the final extrusion, CLEAR PETG will be the most flexible. Rigid.Ink brand, tend to put quite a bit more fillers into their filament which gives it good opacity, but also results in a stiffer print, but is more expensive as these fillers cost money.
Cheaper filaments tend to use less fillers so end up with more flex.
If you are looking for strength and stiffness, then you could look at Poly-carbonate, but this has it's own set of challenges.
Then there are modified PLA's with Carbon fibre or fibreglass added, but a lot are not what they seem so research is needed on the individual filaments.
If your willing to spend a bit more, then try an opaque white Rigid.Ink PETG, or Opaque black.
Here is a link to show different material properties for you :
RE: PETG weaker than PLA.
Make sure that the part cooling is turned down for PETG. Increasing temps by 5C may help with inter-layer adhesion. What layer height and extrusion width are you using?
RE: PETG weaker than PLA.
Aren't 145/155 too high already?
Part cooling was turned on. I don't see how it can affect my prints in mean of strength across the layers (perpendicular to bed), but I may be missing something.
As for layer height - standard 0.2mm, and extrusion width - also default 0.45 (with exceptions for 0.42 on first layer, and 0.4 on top solid infill; rest is as mentioned).
RE: PETG weaker than PLA.
If I understand you correctly, you use the PLA printer profile and adjust it for PET. It doesn't work that well.
Use the profile for Generic PET and it will be good.
PLA writes with 100% air velocity on the fan but the profile for PETG uses only 30-50% air velocity.
If you print PET with too high air velocity, the layers do not bind together well enough.
Bear MK3 with Bondtech extruder
RE: PETG weaker than PLA.
Aren't 145/155 too high already?
It depends on the filament. That brand recommends 230-250C. Assuming you really meant 245C and that you're printing in cool ambient temps, a bump might help with adhesion. However...
Part cooling was turned on. I don't see how it can affect my prints in mean of strength across the layers (perpendicular to bed), but I may be missing something.
That cooling is offsetting the benefit of the higher temps needed to achieve good inter-layer adhesion with PETG, resulting in exactly the results you're getting. The stuff literally needs to melt together to provide optimum strength. Start by reducing or disabling part cooling with PETG. Add only as much cooling as necessary for stringing and bridging.
As for layer height - standard 0.2mm, and extrusion width - also default 0.45 (with exceptions for 0.42 on first layer, and 0.4 on top solid infill; rest is as mentioned).
The parameters should work fine.
RE: PETG weaker than PLA.
If I understand you correctly, you use the PLA printer profile and adjust it for PET. It doesn't work that well.
Use the profile for Generic PET and it will be good.
PLA writes with 100% air velocity on the fan but the profile for PETG uses only 30-50% air velocity.
If you print PET with too high air velocity, the layers do not bind together well enough.
Okay, maybe I put it in wrong words, sorry for that. What I meant was that I used Prusa PET built-in profile, and things I changed (infill density nad pattern) were the same. I know difference between those profiles, and I am aware that process described by you is invalid. Thank you for your reply anyway - straightening some mistakes may be helpful for other people looking for answer.
It depends on the filament. That brand recommends 230-250C. Assuming you really meant 245C and that you're printing in cool ambient temps, a bump might help with adhesion. However...
Yeah, thats exactly what I meant, another mistake, sorry for that. At current temps adhesion is sufficient enough, though.
That cooling is offsetting the benefit of the higher temps needed to achieve good inter-layer adhesion with PETG, resulting in exactly the results you're getting. The stuff literally needs to melt together to provide optimum strength. Start by reducing or disabling part cooling with PETG. Add only as much cooling as necessary for stringing and bridging.
I get it now. At current profile fan speed is set to 30%-50%, as @rhdreambox mentioned. So, given ambient temperatures, I am going to check results with fan speed set to 10%, because for 255C stringing was already noticeable. I will post results or further questions.
Thanks for replies, for now.
RE: PETG weaker than PLA.
Try just turning the cooling fan completely off for PETG except for bridging. Unless you are printing parts with lots of overhangs, that might be all you need.
RE: PETG weaker than PLA.
Ok, so long story short I printed last set of bearing holders at 0% fan speed with 10% bridges. Final product is more rigid and overall structurally durable than first PET prints, but while I am holding both PLA parts and final PET parts, I feel that PLA is more rigid and solid, while PET one flexes noticeably more. I don't know much about materials, but I heard that PET has better mechanical properties, so it's good for making mechanical parts out of it. And flexing doesn't go along with it, imo.
Anyway, for the clips - I don't think there is way it will break, and for "slipping" bearings in flex is welecomed feature.
But.
I still want to print with PETG, and get better prints. I am missing something else? Or just my understanding of material properties is incomplete?
RE: PETG weaker than PLA.
PETG is flexing more then PLA. Maybe you're expecting something different from PETG.
If you don't get any layer separations then your print is as strong as it can be.
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RE: PETG weaker than PLA.
PETG will flex a bit more than PLA, PETG is closer to ABS in that regards. The benefit of PETG vs PLA is PETG is not as brittle. I'd also suggest reducing the infill. A 20% infill is often more than enough for good part strength and if it's not try increasing perimeters over increasing infill, it'll save you on filament and usually print time as well.
RE: PETG weaker than PLA.
[...] I don't know much about materials, but I heard that PET has better mechanical properties, so it's good for making mechanical parts out of it. And flexing doesn't go along with it, imo.
"Strength" is a relative term and can mean different things. Do you mean pulling, crushing, bending or twisting forces? These are all different properties. Do you want a part to bend or shatter when too much stress is applied? PETG is generally considered more suitable than PLA for mechanical parts because it is less prone to shattering, although hardly immune to it. Nylon is considered excellent for mechanical parts, won't shatter but is extremely bendy.
RE: PETG weaker than PLA.
Not all PETG is the same, different manufacturers use slightly different blends which will affect the final rigidity, strength etc.
For instance my experience, SUNLU White can be quite stiff since white will have quite a bit of titanium dioxide added to get the whiteness, this acts as a filler which will help stiffen the final extrusion, CLEAR PETG will be the most flexible. Rigid.Ink brand, tend to put quite a bit more fillers into their filament which gives it good opacity, but also results in a stiffer print, but is more expensive as these fillers cost money.
Cheaper filaments tend to use less fillers so end up with more flex.
If you are looking for strength and stiffness, then you could look at Poly-carbonate, but this has it's own set of challenges.
Then there are modified PLA's with Carbon fibre or fibreglass added, but a lot are not what they seem so research is needed on the individual filaments.
If your willing to spend a bit more, then try an opaque white Rigid.Ink PETG, or Opaque black.
Here is a link to show different material properties for you :
https://rigid.ink/pages/filament-comparison-guide
Normal people believe that if it ain’t broke, don’t fix it. Engineers believe that if it ain’t broke, it doesn’t have enough features yet.
RE: PETG weaker than PLA.
(I hate these forums, timing out when editing a post!)
I was going to add, the Sunlu can snap easier than other PETG due to the formulation they use whereas the Rigid.Ink opaque filament tends to be strong and stiffer than cheaper PETG filaments and is less prone to snapping.
My experience with Rigid.Ink opaque black is that it prints well and is what I use for printer parts where I am willing to spend the extra money for a good strong relatively stiff part and have had success with this particular filament on really small parts where other PETG's have simply been to soft and result in a poorly detailed part. But for general non critical parts, I will use a cheaper PETG filament.
For some parts where strength and stiffness were the primary concern I used Polycarbonate, also where high temperatures are experienced.
I describe Polycarbonate as PETG on steroids, but not easy to print.
Here is a link for you showing what different filament materials properties are in general:
https://rigid.ink/pages/filament-comparison-guide
Normal people believe that if it ain’t broke, don’t fix it. Engineers believe that if it ain’t broke, it doesn’t have enough features yet.
RE: PETG weaker than PLA.
Sorry for not replying for so long, I was kinda busy.
I managed to find some time to check out your suggestions though, and I have to say - strength of the prints increased greatly, as well as overall appearance of parts. All I did was setting temps to 245/255 and completely disabling fan, with exceptions for bridging, where it's 10%. For cetrain parts I also halved bridging speed and prints come out much better. So much, that when I printed some part my friend needed at work, despite incorrect slicing I did (no supports everywhere they should be) he was stunned and was looking at part while driving (while in traffic jam) instead of focusing on road. And he is hard to impress.
So, for everyone having this problem, that's what I did when printing in 18/20*C ambient temperature.
Thanks everyone for help, +1's are on the way.