First layer question



  • This is an issue that I have been seeing for a long time. I have worked around it but am wondering if other people have come up with a better solution.

    The basics:
    PETG, 230C nozzle temp, 85C for bed temp (both of these are for the first layer)
    1.75 mm filament, 40 mm/sec speed for first layer, 0.4 mm nozzle. 0.5 mm line width. 0.25mm first layer thickness.

    The problem:
    When printing large(ish) flat areas (currently printing light switch cover plates), every once in a while the filament being laid down on the build plate doesn't adhere properly and for a lack of better words it 'bounces' off the build plate before recovering and sticking again.
    This happens on a clean glass print bed. There is nothing on the glass as an adherence improver (such as glue, tape or hair spray)

    What I do to get around the issue:
    From all my testing, it appears that this happens when the nozzle is ever so slightly below the optimum glass to nozzle distance. I increase the glass to nozzle distance by 0.05 mm and most of the issues go away. Sometimes I need to go up by 0.1 mm but if I go ever so slightly too high then my adhearance to the glass plate goes to crap. It's a very delicate balance between a perfect mirror finish surface and a surface that has some spots where the filament is not flush with the glass.

    The Question:
    Have you run across this issue? Have you tracked down why it's doing this? Have you got a solution that is not as sensitive to the nozzle height?!

    build plate imperfection 1.jpeg

    In the attached photo you can see the issue. Note that further to the right you can actually see that the nozzle is apparently too high (slight grooves between the lines of filament laid down)



  • Hi,

    For me slowing the first layer to 20% of normal print speed made the most difference in getting the filament being laid down to adhere.

    Frederick



  • Two things stick out for me there...85C seems too hot a bed temp since the Tg of PETG is usually in the 75-80C range. I prefer 75C for my first layer and then down to 70C for the rest.

    Second thing is 40mm/s is too fast for the first layer of petg and should be more in the range of 20-25mm/s.

    PETG does not like to be pressed onto the bed like PLA or ABS do and it can cause it to be dragged back up by the nozzle. It does take a bit of practice to get it to work well. i've started to really like printing PETG on a textured PEI bed but that's not always the surface finish you may want.



  • Thanks for the replies. I will give all suggestions a try.

    Some comments:
    I get good adhesion to the plain glass at 85C, Going to 80 for the first layer will work but the range of acceptable temperatures with PETG is incredibly narrow. 85C is the maximum allowable and still leave the glass plate in one piece but you have to wait quite a while for cool down before the print comes off. 80C works well all around and I believe at 75 the adhesion is compromised sufficiently for the print to pop off on occasion.
    I chose 85 for the first layer to keep larger flat pieces from curling up at the corners (I also use a brim) and to get better adhesion and therefore less of the problem areas.
    I will try 20 mm/sec ... normal print speed is 50 mm/sec. I used to run at 50% for the first layer but got impatient .... this may be a side effect that I never connected with the faster first later.
    In order to make a line 0.5 mm wide with a 0.4 mm nozzle, you have no option but to press the first layer down. At that point, adhesion to the glass is controlled by the glass temperature. I believe that most if not all cases of "petg doesn't like to be pressed down" arise when the print takes the glass surface with it when it is removed.
    Well ok, the other aspect is the petg climbing up the nozzle as mentioned .... but that is fixed with extrusion factor and can be tuned out for subsequent layers to reduce nozzle filament pickup.
    The other thing, if I want a totally flat surface with no (or minimal) grooves between laid down lines, I can't just let the filament plop onto the glass plate because it would stay round with grooves between lines.

    Anyways, thanks for the suggestions, I will try the slower first layer right away because that seems to me to be the most promising change.



  • Some thoughts that come to mind:

    • Do you run automatic bed leveling? It helps maintaining consistent distance from the bed.

    • Isn't 230c too low for petg? I print 255c first layer and 245c for the rest of the layers. Whatever 255C and 245C mean on my printer.

    • I have no experience printing on glass. I use 60C with PEI bed.

    • Slowing down will definitely help.

    • Is the defect always at the same location on the bed? Is the bed clean? With PEI, once in a while I scuff it with wet 1000 grit sandpaper for better adhesion. I don't know if this is applicable for glass.

    • You may want to set your slicer to pause after the first layer. This way you can inspect it and cancel the print if it's defective.



  • @zapta said in First layer question:

    Some thoughts that come to mind:

    • Do you run automatic bed leveling? It helps maintaining consistent distance from the bed.

    My bed leveling routine takes about 3 hours so it only gets run once in a blue moon. The resulting mesh bed map is loaded for every print.

    • Isn't 230c too low for petg? I print 255c first layer and 245c for the rest of the layers. Whatever 255C and 245C mean on my printer.

    It might be a little low but keep in mind that temperatures aren't absolute - they are relative to each other when you a measuring with the same setup. As you realize, 230 on my printer might be 250 on your printer.

    • Slowing down will definitely help.

    I just removed my latest print (with 20 mm/sec for the first layer) - it did not help 😞
    Having said that, I will go back to the standard 50% speed (25 mm/sec in this case instead of 40 mm/sec) as my default.

    • Is the defect always at the same location on the bed? Is the bed clean?
      With PEI, once in a while I scuff it with wet 1000 grit sandpaper for better adhesion. I don't know if this is applicable for glass.

    Sometimes the spot is at the same place, sometimes it is not. The print just finished had two spots at different locations.
    I tried glass cleaning - sometimes it makes a difference ... but only if the glass really needed cleaning. I still get the spots with clean glass but yes, I can have more spots with glass that needs cleaning.

    I will run some tests with printing the same model at the same spot to verify that the spot is really moving ... just in case I don't remember things right.

    • You may want to set your slicer to pause after the first layer. This way you can inspect it and cancel the print if it's defective.

    That is one of my go-to things I do (watching the first layer) but it gets frustrating when you do the same first layer three times before you get a clean first print. I would really like to be able to press the 'go' button and come back to a properly finished print a few hours later.



  • Also print a temp tower and see what it wants to be printed at, as 230c (or whatever you consider that number to equate to) is considered at the very low end of the range for petg.

    If bed levelling takes so long it seems one of two things: a very bad design or a bad setup.

    Levelling with x3 motors takes less than 30 seconds to complete.

    And this is FDM it is not yet fully at the point of press print and wait for the part to be spat out



  • The second cover plate I printed with a slow speed first layer came out perfect. It remains to be seen if this was a one-off or if the percentage of good prints is increased by a slower layer. Gut level feeling says that this will improve my prints.
    I will keep printing with a slower first layer for a while and see what develops
    I will not change any of the other parameters talked about until it becomes clear if changing the first layer speed gives a noticeable improvement (I just love intermittent problems - grrrrr)



  • @jens55

    Hi,

    I understand that you want a smooth build surface but I thought I would briefly mention what I went through.

    I started with glass, had problems, added a build surface which worked fine but it had a texture.

    Anyway, long story short, I am now using the BuildTak system and couldn't be happier.

    I like being able to remove the build surface, since it is attached to the flexible plate, wave it around to cool it if desired and flex as needed to remove the print.

    No longer do I have to wait for the 6mm metal bed with glass plate attached to cool before removing prints.

    They have different build surfaces, one of which I think is smooth.

    Frederick



  • For a time I tried different surfaces. I tried glue and I tried PEI. The PEI ended up curling at higher temperature despite being glued to the glass plate, the glue was worse than plain glass. The secret to glass (IMHO) is getting the bed temperature just right. I do need to 'preheat' the glass by making the initial temperature higher that my print temperature and dropping it just before the print (or giving a lengthy heatup period). This ensures that the glass surface temperature is warm enough.
    It is annoying that the cool down takes as long as it does but I have been screwing around with print surfaces long enough that I can accept the cool down period when everything else seems to work just fine.
    It would be nice to try a removable print surface but to be honest, I don't trust it to lie flat enough short of having a vacuum table. There is also the issue of the build surface being 500*500 ....
    If I loose the surface of a glass plate due to getting my temperatures too high, I can turn the glass plate over and have another go but build tack is a one shot deal. There is also the question of killing the magnets by running too hot a bed.
    To sum it up, I am pretty 'fiddled out' and am more into just pressing the button and let it do it's thing (a la toaster). I could be tempted to try BuildTak if there was more of an up side then just avoiding the cool-down.



  • The oil in your fingerprints is an excellent barrier to bed adhesion.

    A spot like that, I would expect it to be a contaminant like a fingerprint.

    And be very careful with PET and glass. Get the temp too high and you will weld the PET to the glass. Like, ripping chunks out of the surface of the glass kind of welded.

    Getting a perfect first layer is really hard to get consistent.



  • @theruttmeister said in First layer question:

    The oil in your fingerprints is an excellent barrier to bed adhesion.

    A spot like that, I would expect it to be a contaminant like a fingerprint.

    Yes, a spot like that 'could' be a contaminant but in this case it was not. See my comment above about cleaning the glass plate. Also, note that two prints done on the identical spot on the build plate showed problems on one print and none on the second print.

    And be very careful with PET and glass. Get the temp too high and you will weld the PET to the glass. Like, ripping chunks out of the surface of the glass kind of welded.

    Been there, done that, current build surface has a big chunk missing (now on the underside)

    Getting a perfect first layer is really hard to get consistent.

    Yep ....



  • @jens55

    What are you using to clean the glass?



  • Bon Ami - works really well!



  • Another update - I have now printed three cover plates, the first one had some issues but the next two were perfect - I am very optimistic about the speed change.

    Temperature was brought up as a potential issue for PETG. I dug out the details - Nozzle: 200 - 240 C, bed 75 - 85 C .... so I am right where I should be.

    Thanks again to all that offered their input! To be honest, I could have stared at the settings til the cows come home and not seen that I had set it for higher than the recommended speed. I had been printing at that speed for quite some time. It's great to be able to bounce these kinds of things off the people in this forum because although it might stick out like a sore thumb to everybody else, sometimes it's difficult for the one staring at the problem to see the trees for the forest!



  • @jens55 said in First layer question:

    It would be nice to try a removable print surface but to be honest, I don't trust it to lie flat enough...

    I have a 300 x 300 bed and it is more than flat enough. Not sure what you would need for 500 x 500.

    I cannot imagine that I will ever use glass again.

    I could be tempted to try BuildTak if there was more of an up side then just avoiding the cool-down.

    Don't forget the different build surfaces you can swap in/out as needed. The only part that is attached to the printer is the magnetic part.

    The build surfaces are adhered to the flexible plate. I've got all of the BuildTak build surfaces but there is nothing to prevent you from attaching something else. All you need is to purchase as many flexible plates as you have build surfaces you want to use.

    As to too much heat killing the magnets you would have to check with BuildTak.

    Frederick



  • @jens55,
    Just curious - what kind of extruder/hotend setup are you using?

    Cheers,
    Kolbi



  • Chimera clone, Volcano clone hot end. The extruder is a BMG clone. The printer is a highly modified Creality S5


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