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Gaps between top layers and walls


3rdpig
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Posted · Gaps between top layers and walls

Hi @3rdpig, glad to hear that using the wider line width has helped. I used to use S3D a while ago and I am sure that 0.48 was the default line width for a 0.4 nozzle and I just settled for 0.5 as it makes designing easier. If you search the internet you will find a few discussions on this subject.

 

Hi @Link, I don't think there is a bug causing the gaps. It's just hot plastic doing funky stuff!

 

I guess the moral of story (if there is one) could be that FDM printing is just one big approximation.

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    Posted · Gaps between top layers and walls

     

    I have a photo from ages ago of the settings in Slc3r for a Prusa I used to have, they also use a wider extrusion width than the nozzle !, interesting. Seems Cura is the only slicer to default to less than the nozzle 

     

     

     

    IMG_0071.thumb.jpeg.ca172b49059d7d4b3eeb30f81d4499a0.jpegI

     

     

     

     

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    Posted · Gaps between top layers and walls

    Yes, you're right, I used to use slic3r also and that defaulted to lines wider than the nozzle width.

    When I first started using Cura I noticed that the default line widths were small and I just ignored that and carried on doing what worked well for me.

    Maybe on UM machines using a narrow line width is better?

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    Posted · Gaps between top layers and walls

    I read that UM feel it gives better detail, on my UM 2+ I get better results with 0.4 than I did with 0.35, I haven’t gone wider, maybe I will try it. 

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    Posted · Gaps between top layers and walls

    I printed another one with Ironing 10% turned on, (something I found helped minimize the cracks but didn't totally cure them) and the results are really good. A tiny bit too much plastic, but I bet I can get it dialed in even better. And TBH I'd rather take a fine sanding sponge or an emery board and remove a bump or a ridge than try to fill cracks with a 3D pen then sand it down.  Although the whole thing has improved my skill with a 3D pen, it's still something I'd rather not do if I can help it.

     

    This really made my day, thanks again!

     

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    Posted · Gaps between top layers and walls
    1 hour ago, smartavionics said:

    Hi @3rdpig, glad to hear that using the wider line width has helped. I used to use S3D a while ago and I am sure that 0.48 was the default line width for a 0.4 nozzle and I just settled for 0.5 as it makes designing easier. If you search the internet you will find a few discussions on this subject.

     

    Hi @Link, I don't think there is a bug causing the gaps. It's just hot plastic doing funky stuff!

     

    I guess the moral of story (if there is one) could be that FDM printing is just one big approximation.

     

    @smartavionics When I changed the line width from .4 to .5 my wall thickness stayed at 1.2 but the number of walls went from 3 to 2. In this circumstance should the wall thickness and number of walls stay a multiple of .5?

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    Posted · Gaps between top layers and walls
    5 minutes ago, 3rdpig said:

     

    @smartavionics When I changed the line width from .4 to .5 my wall thickness stayed at 1.2 but the number of walls went from 3 to 2. In this circumstance should the wall thickness and number of walls stay a multiple of .5?

     

    Obviously, if you want to keep 3 walls then either increasing the wall width or explicitly setting the number of walls to 3 is required. Personally, I tend to use 2 walls more often than 3 but it just depends on how strong you need the part to be.

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    Posted · Gaps between top layers and walls

    My problems haven't ended. I decided to print a section of a normal part and not only were the gaps back, they were worse then ever and in more places. I'm printing some more test pieces out now and I'll know more when they finish. 

     

    At least I found a use for all those mostly used spools of filament I've got laying around. But I'd rather be making money.

     

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    Posted (edited) · Gaps between top layers and walls

    That’s a pain, I have to admit I was surprised the line width worked as ‘in theory’ it shouldn’t as the slicer moves the lines to compensate for the extra width so the gaps ‘should’ remain (which they have). 

     

    Have you checked the infil below the walls ?. Are you getting gaps on all layers or just the top ?  Can you try another material, even a different colour of the same, just to rule out the material flow. I had some black pla which seemed to have such bad layer adhesion that I had gaps all the time, tried another filament and it was fine. Do you have a spare nozzle to swap and try that ?  Also what is the ambient temperature in the room. I had some issues with gaps when the room was really cold. If you increase the temperature by 10 deg does it go ?

     

    Also try some cleaning filament. Ultimately either the plastic is not sticking to itself once laid down or you are slightly under extruding. It could be you have something in the nozzle, a small clog which needs to clear.

    Edited by Link
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    Posted (edited) · Gaps between top layers and walls

    Have you tried rotating the model, for some reason that stopped the gaps for me. That was def a Cura thing. Wish I knew what it was 

    Edited by Link
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    Posted · Gaps between top layers and walls

    @Link Yes, I rotated the models, it changed the location of the gaps but didn't fix it.

     

    I did find out what's causing this new issue. It's not the same as the old issue, this is worse and different. It's not just thin cracks, it's larger gaps, large enough to stick a pencil point in. Somewhere along the way top/bottom pattern got changed from Lines to Zig Zag. Changing that back put things right. Looking at it in Craftware the outer "zig" would sometimes happen over the open area between infill lines (I'm using Grid and 20%) and didn't contact the inner wall enough to support it, so it dropped into the infill. I suspect one of the "expand" settings would probably fix this, but just setting it back to Lines did the trick.

     

    And now that I have Craftware installed I'm going to print a test with it later and see how I like it. Gotta another job to kick out first though.

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    Posted · Gaps between top layers and walls

    Glad the original issue is still ok, I can’t help but think there is some Cura quirk in here. Something doesn’t add up. Wish i knew what it was. 

     

    I found this info on S3D website 

     


    If lines are printed so thin that there's a gap when their shouldn't be, adjusting either Extrusion Width or Layer Height will NOT fix the problem. For example, if you have a 20% gap between walls that should be solid without a gap, and you make your Extrusion Width larger, your gap will still be 20%, but will now be a larger gap because the lines are now larger and further apart from each other (the print resolution is lower). You didn't get rid of the gap, you just enlarged the lines, and the line spacing, so the 20% gap appears wider, but is still there at 20%.

    Likewise, If lines are printed too thick and are overlapping each other, adjusting either Extrusion Width or Layer Height will NOT fix the problem. For example, if you have a 20% overlap between walls, and you make your Extrusion Width smaller, your overlap will still be 20%, but will now be a smaller overlap because your lines are now smaller and closer together (the print resolution is higher). You didn't get rid of the overlap, you just shrunk the lines, and the line spacing, so the 20% overlap appears thinner, but is still there at 20%.

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    Posted · Gaps between top layers and walls

    I found another topic on this, same issue. Some ideas about the walls cooling and shrinking away from the other wall. I can relate toe this as when I had the problem I could see the gap get larger as the print cooled.

     

    I wonder whether S3D prints the walls in a different order and maybe that is the key difference ?, can you tell from the Gcode ?. 

     

     

     

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    Posted · Gaps between top layers and walls

    The S3D gcode posted above is using an extrusion multiplier of 1.03. Have you tried telling curing to use a 103% flow? Maybe it just needs a little more filament?

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    Posted · Gaps between top layers and walls

    I have looked into this a bit more and the constant similarity between this and when I have seen it is that the gaps appear at the layer start point, the wall lines are started from the same point due to the z alighment and this is the area the gaps start. It really goes seem like the other existent walls have shrunk and the new wall doesn't quite meet the existing. That may explain why rotating the model changes the behaviour as the z seam alignment will move. Would be worth trying to set the seam alignment to random and see if the gaps move. 

     

    I also found that if I printed two models at the same time the issue went away, the print had to perform a retraction and move between parts which I assume changed either the wall print order and/or seam alignment position.

     

    I have seem this problem on both 0.6 and 0.4 nozzles too. And its constant in that it appears at the wall start point

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    Posted · Gaps between top layers and walls

    looking at the model it would be worth trying changing the 'Seam Corner Preference', I am not clear if setting this to 'hide seam' for instance is having some odd affect in some scenarios, however setting this to 'none' certainly seems to move the seam point and worth a go

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    Posted (edited) · Gaps between top layers and walls
    13 hours ago, smartavionics said:

    The S3D gcode posted above is using an extrusion multiplier of 1.03. Have you tried telling curing to use a 103% flow? Maybe it just needs a little more filament?

     

    @smartavionics I tried that back when I was originally trying to solve the issue, I kept increasing it until I started getting blobs and still had the cracks. I haven't tried increasing it again since I increased the line width. I may try it on a test piece later, but right now it's working really well. I'm printing a full size piece sliced in Cura and, with the exception of a tiny gap at the small hole, it's better than the S3D sliced part. I'm very happy with the results, the top surface is the best I've ever gotten and that's without ironing.

     

    There is another problem but it happens in Cura but not in S3D, and that's a tiny gap around smaller holes and neither the line width or adding a fourth top layer has fixed. Here's a picture, this is an 8mm hole, 7mm deep. If it was on the surface it would annoy me, but down inside another hole it's almost unnoticeable unless you're looking for it. I'll also attach the gcode for that test block. I wonder if "Outside before inside walls" would help?

     

    UDXkdCxpKwHeQrB2j_4izigC7NYxdUwnZztsu6HrN4n02saWKxWs3c2svEhd2Ff4BTIbvGJ1ZaVYfl5lilclplEmJrpoKozwLKwlFppLZcdPwKqA0tdBtVv1F3jHVrpdZ06F7JWklVHrIMsX5KnZFORRo_bGaSmUAEEDQWYExZ9hiLWKZ4GGM0v7HPiOeCMV4IVHKgl4jimxyzlqpLWjoGwuHpZxQ0O9NDjS7Lqmf-VF78h_Qc-Z6fxs-o8CBlGrU5ULXVwhjfnrUjiYXci-aTXM1YILIgNwLazbCWBhYq3hqKif8LN-7H3QcZXaOI7pnDdNLpxNSqct0x2qszcAd7NpcIn5vVSYMwaBGu3W8JkLlkxdoBVaUzVmchpraHO4mUtCaxgaxPwOfhq-UXDSxsE5jtjY6jdrs4FP986V3Yy4u25bc5M6e7ml_Lvz5ex_xDD3SdYRan2cLrgi1XhH8lZbjSqULOOLps8vDSjkII1HTdMDBbP2Msyv6yji9a0K2Kr2fGWSNsajc5KmHHWLIJsfrvGOOJhp2h0PsRGj15lwh9nNHumQMiO0_rQ7Pbzs0PI5wgHh2mCAKiCsGc0Dr3xbu4AiqrFaIeshblipJnXSoxoSFivgijz4gUSymaAw=w715-h953-no

     

     

     

    12 hours ago, Link said:

    looking at the model it would be worth trying changing the 'Seam Corner Preference', I am not clear if setting this to 'hide seam' for instance is having some odd affect in some scenarios, however setting this to 'none' certainly seems to move the seam point and worth a go

     

    @Link I've tried changing this setting just to get rid of the necessity of removing the seam when the part is done. I usually have Hide Seam and Sharpest corner selected. Let me know if you find any difference in that. I may play more with it later to see if it helps cure the problem in the photo above.

    og test 3.gcode

    Edited by 3rdpig
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    Posted · Gaps between top layers and walls

    @3rdpig what line width did you settle on in the end ?, what did you start with 0.35 ?. 

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    Posted (edited) · Gaps between top layers and walls
    10 minutes ago, Link said:

    @3rdpig what line width did you settle on in the end ?, what did you start with 0.35 ?. 

    @Link

     

    I started with .4 and went to .5.  I also changed my shells from 3 and a 1.2 thickness to 2 and 1.0. 

    I think this is going to work out well for my existing parts since I tend to like to leave 3.0mm between holes and between holes and walls.

     

    I also upped the number of top layers from 3 to 4. Mainly due to the white filament I'm currently using, it shows imperfections much more than colors and the fourth layer really helps that. But the fourth layer doesn't add as much print time or filament use as I'm saving by only using two walls so I may use it for everything going forward.

     

    I haven't printed enough parts yet to be sure, but all the test blocks and the one full sized part suggest that this might be a big improvement. I'm sure hoping so. If nothing else, this is the first really good looking part of this type I've made with Cura. Others have been ok, but not up to what I'd get from S3D.

    Edited by 3rdpig
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    Posted · Gaps between top layers and walls

    @3rdpig interesting, I recently went from 0.35 (the default in Cura for a Ultimaker 2+) to 0.4 and have to admit the parts look way way better, the top surface looks so much better not to mention the walls etc. All this would indicate that Cura seems to work better with line widths at least the size of the nozzle. My parts never  looked as good with a 0.35 line even without actual gaps issue, the top layer looked very rough compared to a 0.4 nozzle. 

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    Posted · Gaps between top layers and walls

    Hi,

    I know this is an old post, but I had simular issues. Because I spent a lot of time searching for a solution, and I used a lot of filament, I hope you do not need to go thru the same learning curve.

     

    I drew the same object all over again I use Sketchup) , and the first print was perfect (cura 3.2.1)

     

    I have a Anet A8 pro. I tried 3 versions of Cura 14.7 (old stuff, included with the printer), Cura 3.2.1, and Cura 4.5. All gave the same problem. In the 2 last versions, I tried everthing which is mentioned in this post. I also tried flipping the object and tried other ways of creating the STL file.  Sometimes it was slightly better: fe. flow rate at 103%, ironing with 15% flow,  skin overlap percentage and infill overlap percentage at 100%,... gave some improvement. (But you know this is not the way it should...).  in the mean time, I printed more then 20 discs (with holes in it - which gave the problem).

     

    I checked my model (skp) inside, outside, everything I could do, but did not found anything special.

     

    So I started from scratch, drew everything again, and first time right.

     

    (I thought I read that also somewhere higher in this post)

     

    Succes.

     

    Karl

     

     

     

     

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