First I just want to comment on strength, PLA and PETG one is not necessarily stronger than the other. The way they break is very different.
I spent many many years building boats so I will reference them A test bar with Carbon finer and epoxy when loaded will not bend for ages then it bends a ting bit and explodes to fragments. The same sample with kevlar it bends and bends and bends makes unhappy crunching sounds bends some more and breaks but usually doesn’t let go completely it just sits at an unhappy 90º dangling held by strands still.
PLA is like carbon epoxy, it doesn’t bend it just shatters. PETg is like carbon it bends and deforms quickly and continues to deform until it fails.
Thomas Sanladerer has an entire series on strength and loads of filaments. CNC Kitchen also spends a lot of time on printed part strength.
Just the beginning…
I don’t know why your petg is failing so dramatically, It should deform first. Odd.
ok, I grabbed a roll of solid Grey house brand PETG, Going to print it up on an Ender 3 V2. its about a 4.5 Hr print so should let you know by the end of the day.
Dry the filament. Even stuff just out of the package. I print with only the house brand on an Ender 3 Pro and 5 Pro using 240/80 1st layer 70 after that. I use a mirror with blue tape.
I am discovering similar issue reported here and I think it may be specific to certain colour or perhaps manufacturing batch. My experiences so far:
I printed white, black, transparent blue, dark orange, and red PETG on a Prusa MK3S at 240C.
I find the white PETG has the best layer adhesion and would flex or tear between layer when loaded to failure. This is what I would expect from PETG.
The black, red, dark orange and transparent blue were extremely weak and brittle between layers and would snap cleanly on layer boundary under minimum load. I could even pull apart 1.5mm thick wall (approx. 3 perimeter with 0.4 nozzle) just with my fingertips.
All of these were printed under the same slicer settings at 0.15 layer height. But I observed similar behaviour with different layer heights.
To rule out moisture issue, I retested after drying all spools at 68C for 8 hours but observed the same result.
Finally, I tried another PETG brand for comparison and printed it under the same settings and it produced a good layer adhesion like the white filament.
So unfortunately, while I love the colours, I could not use them for any functional parts.
Edit: added pictures
These are all thin walls printed with the same settings. I tried to fold them across layers.
I have not printed a massive amount of 3DPC brand Petg I have printing many rolls of a different manufactures brand. I found some colours need a slightly elevated temp. I seemed to me to be related to darker colours. I would suggest a temp tower for the ones causing issue you may find it resolves the issue. Or not you are not the first to report brittle PETg prints with 3DPC filament.
I did try cranking the temp up to 250C. Slightly better adhesion but much worse surface finish. If I’m desperate I will over-extrude as well, but I prefer not since it usually cause other problems.
Ruled out clogging or extrusion multiplier issue, as I can consistently reproduce the result every time I switch filament. I am using an enclosure that I vent out a little bit for PLA and PETG to prevent overheating, so that should rule out draft.
After a few more testing, I can conclude that printing at 250C consistently gives me a workable layer adhesion. Parts no longer break cleanly at layer boundary. However, at this temperature, the stringing and blobbing becomes quite severe. And this is after recalibrating linear advance, retraction, z-lift, etc. for this temp. I also notice that the black filament produced a lot more blobs than other colours.
My current suspicion is that there may be some moisture related issue that I had not been able to fully solve. I have read that the issue of brittle part, stringing and blobbing can be attributed to wet filament. Also read somewhere that clear plastic packaging is not really impermeable to moisture. So the next thing I will try is to dry the filaments again for maybe 12 hours. It is possible that the drying method was not too effective due to the spool’s fully enclosed sides. Perhaps only the outermost layer of the spool was dried and longer drying time is necessary to diffuse the water. Unfortunately I don’t have a method to measure the filament’s moisture content easily to validate this.
Could be moisture. Many brands are pulled off very large spools so they sit around in open air potentially for a while before being packaged. The simplest is try another brand. I often use ecotough Petg, Backtobasics I just got some it prints quite well, it is recycled bonus there. Prusament PETg is really good too.
Dry your filament. I print a lot of house brand PETG, and you have to dry it before loading. You will be chasing your tail trying to fine tune your settings until you start with a good, dry filament.
