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ABS What would cause this to happen while printing?

Discussion in 'Printing Filament' started by SoLongSidekick, Apr 4, 2014.

  1. SoLongSidekick

    SoLongSidekick Active Member

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    So confused, it looked like this ABS print was going beautifully. I came home and noticed enough cracks finally developed to make the entire structure topple and the print fail. Hotend temp 230° bed temp 85°. Was stuck beautifully to the print bed even after failing, so confused. Why would it start cracking after being laid down beautifully? It looks like the cracks didn't form until at least 50 layers later. :confused:

    [​IMG]
     
  2. CAMBO3D

    CAMBO3D New Member

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    that's typical of abs.. without a heated chamber abs will tend to warp and crack due to temp changes. Maybe you experienced some air draft that cooled your part too quickly...
     
  3. JohnStack

    JohnStack New Member

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    I'm with Cambo on this; however, I've done fast prints that exhibit this as well. Inter-layer adhesion is all about heat. If you can't do a chamber right now, maybe just slowing your print down might do the trick.
     
  4. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Yes, slow it down and if needed raise the extrude temp slightly. You should not see that severe of inter-layer warp.
    You may still get some minor lamination faults and edge warping is another issue (large, flat prints in particular) but those are just issues with ABS and no heated chamber.
     
  5. SteveC

    SteveC Well-Known Member

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    OK, I'm not much help but some random comments... Is it possible that your max fan setting is too high? I have had delamination occur with too aggressive a bridging max speed. The cracks don't seem to correspond with any layer structure change or bridging that would make the fan speed change so this is probably not the issue.

    These cracks can happen if a corner comes unstuck slightly and the lower layers contract and pull on the upper layers. Not your problem though since it is stuck well and you would see the contraction in the lower layers.

    I have been having more luck with ABS and a higher bed temperature. For my last few prints I set it to 114C which it can barely maintain steadily. Remember that the top bed surface will be more like 15-25C colder than the thermistor. ABS has a glass transition temperature of 105C and it is my understanding that it helps to keep it close to that to reduce stresses. Can anyone with more experience with ABS please comment on this?

    I'm thinking you problem is probably more random drafts and fan speed. I have been keeping a metal draft blocker on the back side of the printer to at least get rid of cross drafts.
     
  6. tesseract

    tesseract Moderator
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    It is simple it is a characteristic of ABS without a heated chamber. ABS cools amazingly fast so as one layer cools it contracts and the next layer is hot and then it contracts build stress and then just like in good ol California the stress builds up and bam you have an earthquake or a print quake and you end up with cracks and seperation etc. In order to succeed you will need to somehow regualte the ambient temp as well as the abs temp currently a heated chamber works the best
     
  7. JohnStack

    JohnStack New Member

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    BTW, you can just turn off the fan with ABS. You don't really need it. Let it cool on its own...
     
  8. JohnStack

    JohnStack New Member

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    You know, I always learn something new on every visit to every forum. I didn't think of the bed surface temp being lower than that of where the thermistor is at. Cool!

    Good idea with the "draft blocker". Last year, I saw someone make cone to fit over the head of a delta printer. Pretty silly contraption - but a killer maker will try anything I guess.
     
  9. Peter Krska

    Peter Krska Active Member

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    For those without a heated chamber, what if you add a heat gun set to a certain temp and have it blowing hot air onto the print as it goes along making it a constant temp until it's done?


    Sent from my iPhone using Tapatalk
     
  10. JohnStack

    JohnStack New Member

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    Interesting idea - but I think it would add quite a bit of variability to the mix.

    I think if you really want to control things without a significant amount of $$ or work, you might consider getting something like window tint or really thick clear poly and a little velcro on double-sided tape. The Robo3d printer cover structure lends itself quite well to being it's own enclosure. Maybe have it sit just slightly above the bed on both sides. There would be enough heat coming from the bed to keep the temp in the enclosure pretty consistently warm.
     
  11. tesseract

    tesseract Moderator
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    B

    Both of these have been tried the so check around on the forum. Their are issues with each the heat gun does ad d a lot of un knowns as john stated the poly film coat does work to a degree teh problem is that as the heat increase and if the belts and other components are heated they can change length so belts become looser etc. so these are thing you should try to guard against.
     
  12. SteveC

    SteveC Well-Known Member

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    Yes, I put a thermocouple with thermal grease on the top of he bed and it was consistently 15-25C colder depending on the location.
     

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