How Mesh Bed Leveling Went Wrong for Me (and how I fixed it)

Discussion in 'Calibration, Help, and Troubleshooting' started by Ephemeris, May 28, 2016.

  1. Ephemeris

    Ephemeris Well-Known Member

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    This tip is especially important for co-polyester users, but it's good to understand regardless of your preferred filament type.

    Because I wasn't used to the BigBox infrared leveling scheme I've gotten some rotten prints because the first layer wasn't sticking well enough. This has been particularly true with colorFabb HT. Hopefully my analysis of where I went wrong will help someone.

    Currently I do everything with the various Eastman Chemical Amphora co-polyester variants: Taulman nVent, colorFabb nGen, colorFab XT, and for the last week, colrFabb HT. (I believe E3D Edge is also one of these.)

    What all of these have in common is a low viscosity, low surface tension tendency to ooze and string. This is usually manageable by tuning your retraction settings and it has no effect on the first layer except for some mess due to strings. Or so I assumed!

    The problem is that, after a print when the hot end has cooled, the ooze almost always will have left a tiny bump of hardened filament just below the nozzle tip.

    This is no problem for the next print, but what if you've changed something and need to rerun mesh bed leveling? Now we are in a world of hurt. Typically, leveling needs to be good to +/- 0.1 mm. I can pretty much guarantee that little hardened droplet of filament on the hot-end tip is thicker than that. This will significantly throw off the feel of your thickness gauge when doing MBL.

    Long story short, when doing mesh bed leveling, make sure there is no filament residue below the brass nozzle tip. The easy way for me is warm up the hot-end, and then set it to cool-down. I use a metal scraper to remove the ooze until it cools sufficiently that no more ooze appears.

    I hope this helps someone else.
     
    #1 Ephemeris, May 28, 2016
    Last edited: May 28, 2016
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  2. mike01hu

    mike01hu Well-Known Member

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    Excellent points and I fully concur with your actions, as this is what I do no matter which filament is in use. I always retract a good 10 to 20mm with the nozzle preheated then wipe the nozzle with kitchen paper to remove all traces of filament, then home the bed with a piece thin card under the head while it cools before checking the initial clearance to see if anything has changed.
     
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  3. Alex9779

    Alex9779 Moderator
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    I do exactly the same! :D
     
  4. R Design

    R Design Well-Known Member

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    Haha @Ephemeris this is familiar to me.

    I tend to do my mesh bed levelling with the nozzle HOT knowing that the back and forth movement of the paper will draw away any ooze droplets.

    (Happened on this technique by accident because generally when I'm levelling I'm itching to get printing or I've interrupted printing to redo everything.)
     
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  5. Spoon Unit

    Spoon Unit Well-Known Member

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    I sort of settle on heating the nozzle to about 140 for PLA and 160 for Edge/XT. This seems to be about the point where the little blob is just malleable enough to move and just sticky enough to carry surrounding material with it. A pair of needle-nose pliers pulls the blob and it's cohorts out of the way. I use to same settings to clean the nozzle up.
     
  6. Henry feldman

    Henry feldman Well-Known Member

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    I also level hot, as I figured (I'm sure someone like @Alex9779 has software that can calculate it exactly) the nozzle must expand as it gets hot, so leveling hot would be more accurate. No idea if it's true (i.e. there is already compensation built in) that it matters, but figured why take the chance...
     
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  7. Spoon Unit

    Spoon Unit Well-Known Member

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    Lol. I hadn't thought that far, though I do apply that kind of thinking to PID tuning. But I love it anway.
     
  8. mike01hu

    mike01hu Well-Known Member

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    Interesting point Henry. Today I re-levelled at 285C and the settings were around 200nm off from the previous settings but I had been around tightening screws again.
     
  9. R Design

    R Design Well-Known Member

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    I wouldn't complain about 200 nanometre resolution!
     
  10. mike01hu

    mike01hu Well-Known Member

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    No it's not a problem but it was just the difference between cool and hot although I'm not so sure as I had been tightening screws beforehand as I said. In general the mesh levelling is excellent and my first layer is uniform and is as good as the resolution of my callipers over a good area of the bed.
     
  11. Spoon Unit

    Spoon Unit Well-Known Member

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    Thinking about all this, I've come to the conclusion that it doesn't really matter whether you level hot or cold; either way you're probably not going to get it spot on and will want to use Tune > Z Bed to perfect that first layer.
     
  12. Alex9779

    Alex9779 Moderator
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    That is how I see that too. Leveling is for the general relation of the bed to the nozzle.
    Sure is also saves an offset of the endstop hit point in relation to where the nozzle has a certain distance to the bed but the goal when leveling the bed is to have that distance almost the same for all spots.
    The perfect offset is then calibrated with the tuning in the first print or a test print after leveling with the tuning option...
     
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  13. mike01hu

    mike01hu Well-Known Member

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    That's true and that is why I use a thin test piece if I am not happy and I don't want to be adjusting for Z offset on-the-fly as that can affect first layer finish. So far, I am getting consistently good first layers!
     
  14. jet

    jet Well-Known Member

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    unrelated to this thread: I'm just starting with nVent today and trying to dial in the settings. Could you post yours over in the Filaments area?
     
  15. Ephemeris

    Ephemeris Well-Known Member

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    I believe Taulman nVent is made frome Eastman Amphora 1800 the same as colrFabb XT. Amphora 1800 is the densest of the Amphora plastics available. I have a few spools of nVent but unfortunately I'm running HT non-stop right now while I try to meet a deadline for some test articles. The good news is several people here have been working with XT so their settings should be applicable.

    As an aside, E3D Edge seems like it may also be Amphora 1800, but I can't swear to it.
     
  16. jet

    jet Well-Known Member

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    I'm dialing it in right now using Eastman's guide for printing with AM1800. I'm printing 20x20x10mm cubes and getting it dialed in slowly-but-surely.
     

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