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  1. #1

    PETG Strength Problems. Layers Adhering

    New to 3D printing, but am a seasoned CNC machinists. I've a pretty good grasp of it though, I think. I'm using a new CR-10S stock. PLA prints perfect. PETG also prints perfect, but the strength is not there. I'm using Hatchbox PETG and a profile I found online for Simplify3D. I'll attach it here. I saw some layers on the bottom of the first print come off by scratching at them so I gave the item I was printing a squeeze and it made creaking sounds and kept squeezing until it broke and it broke along the layers.

    I'v done some test prints with different temp settings and I can't get the strength. The prints come out looking good no matter what I change the settings though. The only thing I didn't do, from what I've read online, is re-level the bed for two sheets of paper, but I didn't read this until after a couple test prints and the prints came out looking great, minus the strength.

    I did test prints at 230, 240, 245 and 250C. When I did a destruction test on those pieces 250 seemed the strongest so I went ahead and started to print a part and one of the overhangs with supports started lifting up. So that's a no go. I'm basically running it at 15mm/s, 35% fan speed, 100% infill (for the part I'm making) and some of other settings that deal with the stringing and other fickle natures of PETG.

    Any ideas? From what I've seen on youtube PETG should be tough as nails. BTW, the part I'm trying to make is a cover for stepper motor 100% infill and .093" thick walls. So I think it's rather beefy.
    Attached Files Attached Files

  2. #2
    Technologist
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    I print my PETG at 240 so your 250 is close. i use no fan for the first layer, then 100%. Looks like you max is only 50. the other concern is 100% infill. That's a lot of plastic trying to cool off. Try dropping down to say 30% ( at least for a test ). Should still be strong.

  3. #3
    Hmm, ok. Interesting. Thanks.

  4. #4
    Super Moderator curious aardvark's Avatar
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    yeah, I'm with you on this. I've tried various types of pet-g and generally found that pla is stronger.
    Even some small clips that need to be flexible - came out better with pla.

    Printed some fairly large brackets recently, that needed to have good impact resistance and a little flexibility.
    Was showing them to someone in my workshop and said, these will flex. And they didn't, just broke really easily.
    Ended up making the final ones from flexible pla - which is genuinely indestructible and rigid enough for what I needed.

    One of our members who works in injection moulding said that pet-g is actually stronger if you print it at a lower temperature. Think I've gone down as low as 225. but the parts just fell to bits.

    For a stepper motor mount - you actually want it to be rigid - so pla would be your best bet anyway.

    I do wonder if pet-g, while easy to print without an enclosed print volume - might actually need one to get to full strength.

  5. #5
    @ Curious, I'm building a stepper mount, but a cover. SO not strength involved, just for the strain relief. It's going on my CNC plasma table that I'm building so it'll be outside in the sun and from what I've heard PLA is no bueno for that. I'm using PLA + and it's prints beautifully.

    Another question how long can I print at 240-250 ish on a stock CR-10S, because I'm trying to recreate the original part I made with Hatchbox PETG that came out perfect with 100% infill and pretty much no stringing, but not as strong as I thought it would be, but can't remember the profile I used as I've messed with it so much. I'm now printing the part again with 30% infill as MJF55 suggested and I'm getting some stringing, not much I can probably brush it off easily. I'm just wondering if my machine is behaving correctly as I'm new to 3D printing.

    I'd like to be in control of all my settings and I'm using a profile I found for Simplify3D, does any other have settings for Cura for PETG so I can enter them manually so I know what's going on? I've read some good articles and most don't mention retracts and all that, they say print like PLA, but lower fan speed, lower bed by another sheet of paper, print slower and print from 230-250.

  6. #6
    Super Moderator curious aardvark's Avatar
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    well I've got items printed in standard pla that have been outside in the british weather for 3 or more years.
    Apart from colour fading slightly, they're as good as new.
    Bird feeders and poo bag dispensers primarily :-)

    It's abs that doesn't like sunlight.

    Not that we get much in the uk. But, cold, damp, rain and just plain misearable - we get a lot of that :-)

    I have one pet-g item that is ridiculously strong. pretty sure it's esun white pet-g. It's a scraper I made to help change a motorhome awning.
    Can't remember what settings I used. But even my dad couldn't break it and he's one of those people who looks on the term: 'virtually indestructible' as a challenge :-)

    It's way tougher and stronger than injection moulded abs.
    It was printed at 0.1mm layer height.
    As were the miniature cogs i made a couple years back. That was colorfabb xt (they call it co-polymer, but I understand it's pet-g)

    Everything I made in pet-g recently has been really bloody awful. Just weak as anything.

    So I don' know if it's down to settings or my pet-g filament absorbing atmospheric water and getting 'wet'

    Pet-g is more prone to stringing than pla.
    Not a clue on your machine. Never had any type of i3 clone.

  7. #7
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    PETG works best for me at 216C. I know that seems low but it is what works best for me. What I am using is a folgertech 2020 i3 clone (bowden E3dV6 mod) and bed temp of 70C on glass coated with aquanet. Cooling the print as fast as I can while printing seems to be the key.

    I print with a .2 first layer then .3 above or variable layer heights using slic3r . Stringing problems I had were resolved with changing the temps. Make sure you have good retraction settings because that can also cause it to string as it tends to be a little thick and not retracting enough leaves too much pressure in the nozzle.

    Using preset profiles was a disaster for me, it allowed me to print okay, but nothing like I can print now with slic3r and me controlling all the variables. I also use firmware retraction and volumetric extrusion in firmware.
    I'm not using expensive filament either, It is Inland Translucent Magenta PETG, for $19 for 2.2 pounds on amazon.

  8. #8
    Thanks. Weirdo though that's almost counter intuitive to everything I've read.

  9. #9
    Super Moderator curious aardvark's Avatar
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    Actually it's not.
    We used to have an injection moulding expert, not been around for a while.
    His advice was to print pet-g at a lower temperature for better layer adhesion.

    have to admit I've never gone as low as 217. But I'll try it :-)

    Currently playing with Tiamats ULTRA. World's first filament with nano-diamonds.
    They only sent out 40 pre-sale sample reels and I've got one :-)

    Currently printing bottle clips, as they're small, got some bridging and don't take long to make.
    Currently on speed tests.
    Up to 200mm/s max speed. Also upped all the other speed settings.

    Supposed to be super strong, easy to print and great for printing at speed.

    Looking good so far :-)

  10. #10
    Cool. Interesting.

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