Bad overhangs on small prints!

[Labern 774]

 

 

I stated that I was printing with normal quality settings gr5. (quickprint) Isn't those the parameters that must work with Ultimaker printers?

 

Work yes, work well no.

there are a lot of factors that can effect the quality of a print and sticking to the quick print settings can limit the ability to get the best results.

Normal setting will be to fast for the advice gr5 is giving.

 

[yellowshark 153]

The quality you want (printing slower will nearly always give you better quality) and the size/geometry of the model dictate the print speed. I doubt that the normal quality settings you are using will be slow enough for getting good quality overhangs.

If your corners are raising 6mm, firstly I do not understand why the printer head is not relocating your model somewhere else and you have a bad setting somewhere in your hardware or software or on your bed; resulting in probably too fast and too hot. It will probably help if you do another print and then post a photo and your precise settings. We need to know

 

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  Layer depth
   
  
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  Wall thickness
   
  
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  Print speed in mm/s
   
  
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  Extruder temp. (actual, not what you put in Cura – yes they well be the same, but they may not)
   
  
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  Minimum layer time – I disagree with some above, I never ever go below 10secs
   
  
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  Minimum print speed
   
  
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  If you have more than one model being printed simultaneously, a picture of the bed so we can see how they are laid out.
   
  
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  Fan settings
   
  
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  The filament being used; e.g. Faberdashery arctic white
   
  
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  Infill %
   
  
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  Top and bottom thickness
   
  
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  Z-lift yes/no
   
  
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  retraction settings
   
  

 

… and leave flow rate and feed rate at 100%

 

Armed with that we can probably solve it for you.

 

[gr5 2,167]

I was printing with normal quality settings gr5. (quickprint)

 

Those change from version to version so unless I install the same version of Cura I don't know what that is. I haven't used quickprint for about 2 years. To find out what speed it is, slice at quickprint-normal, then save the gcode, then switch cura to "full settings" mode. Then click "file" "Load profile from GCode..." then you will see the speed. It's important to know the speed and different version of Cura change this so I recommend you never use "quickprint".

 

[gr5 2,167]

@anon - I've got a fever... for more FAN!

 

[gr5 2,167]

When the head is making a turn in a corner, it drag and lift the material in that layer.

 

Yes. This is a common problem for corners of overhangs and it slowly migrates across the entire overhang but starts in the corners and is worse in the corners. There's a huge discussion plus slow motion videos here:

Skip right to "page 2" and look at foehnstrum's video and read all the posts after that possibly. It's not until around post #39 and later that we really begin to understand what causes the issue.

 

http://umforum.ultimaker.com/index.php?/topic/4094-raised-edges/

 

[gr5 2,167]

Typically the bottom layer is .3mm and the remaining layers are .1 or .2mm thick. The Z axis moves to the EXACT locations (or it tries). So for the bottom layer it would move to Z location .3mm (.3mm above the bed). (calibration is done about .1mm above bed -- in other words it is assuming the paper is about .1mm thick - maybe it's .08mm I forget).

Anyway if the bed is too high then the bottom layer is underextruded a bit and there are gaps between the traces but typically they are small gaps. If the bed is too low then the traces are too fat and you have overextrusion and very commonly you get lots of grinding or skipping on the bottom layer especially during diagonal infill where there is no place for the excess plastic to go.

Once the bottom layer is done, the top layer should be perfectly flat for Z=.3mm. It may be thicker and thinner in spots due to tape or bad levelling etc but unless you are off by more than .3mm it should be very very flat.

Even if there are slight errors they get smaller and smaller each layer.

The exception of course is for overhangs but that hs nothing to do with leveling. Overhangs typically get *worse* each layer. The corners are created like a liquid rubber band that shrinks VERY fast. In a few milliseconds. Already the plastic is about .2% shrunk as it hits the layer below and that causes extra tension (like a rubber band). Most PLA sticks to itself even as a liquid (very different from water!) and so it acts like a liquid rubber band as it goes around the corner and pulls hard enough to lift the outermost corner a bit which results in it being *higher* than the bottom of the nozzle. This effect builds and builds and gets worse each layer. Typically. If you print super slow (5mm/sec) the nozzle will remelt the layer below and fix it. I think it would be a cool feature to slow down to 5mm/sec on overhang corners (say within 5mm) on every 3rd layer.

I haven't tested it but I would expect this affect to be not-as-bad with ABS because ABS has a higher glass temp and so it becomes solid MUCH faster (fewer milliseconds) and has less time to pull. Even so ABS definitely needs fan on overhangs and bridges. I could be wrong about ABS. I've printed with it but haven't tested overhang issues carefully like I have with PLA.

Another fix is to alternate clockwise versus clockwise on alternate layers. This won't work in Cura without doing really bizarre shapes.

Another fix is to add support walls under the corners. This results in ugly corners.

ANOTHER thing causing the problem *may* be printing too fast. When you slow down for a corner, the pressure is still high in the nozzle and so it overextrudes slowing down into the corner and underextrudes accalerating out of the corner. This is definitely the biggest quality issue with UM printers and is fixed by printing at the "jerk" speed which is 20mm/sec (or close to the jerk speed). This might not affect overhangs though - not sure. If your corner is 90 degrees then it won't decelerate if the corner is 20*1.414 or 28mm/sec. So typically I tell people 25mm/sec is the slowest necessary to get amazing quality. 35mm/sec is "close enough" for me and is my typical "excellent but not perfect" print speed.

 

[tottenham12712 1]

?? Leveling only affects the bottom layer and *sometimes* the second layer but that's it. Leveling the bed differently (turning the 3 screws in any combination of directions, amount) will not affect the 10th layer at all. Even if you are crooked by 1mm (printing in air on one side and on the glass on the other) within 5 or so layers things have recovered and leveling no longer maters for the remaining layers.

 

I think you're pushing it to the side a bit too much. Yes after many layers the percentage of error starts to disappear, but when building an overhang precision is even more important. If your bed level is off at layer 1 it will be slightly off all the way up and *can* effect the print.

If you dont believe me just try it yourself only takes a few min and a bit of plastic with that test piece, set the bed too close and run fairly normal settings .15, 50mm/s, and then test again with the bed further away. Id bet you'll see different results. At least I do.

 

The comment that told me that my nozzle is too close to the bed helped a LOT.

I leveled the bed again and set it away from nozzle with a little friction on the paper.

I'm getting decent prints now, still cant print at 60 deg perfect, but I think its not possible to do that anyway.

I will try it again with barely any friction to the paper when leveling to see if there is bigger difference.

gr5 maybe you need to rethink your opinion about bed level? Nozzle is allways closer, every layer, and is effecting the heat of the allready printed layers below.

When the head is making a turn in a corner, it drag and lift the material in that layer. You can see this effect it in my previous posts in the photos.

If you let this happening it keeps building even more than 6mm above the printed layer.

I stated that I was printing with normal quality settings gr5. (quickprint) Isn't those the parameters that must work with Ultimaker printers?

 

Im glad it helped, 60 degrees is a pretty hard overhang, you can definitely keep tweaking your settings but you will need to go into advanced mode to get it. The default settings are only good for so much. If you do activate the advanced settings view you will see what the settings currently are. My guess is .1mm height, and 50mm/s.

 

[gr5 2,167]

If you dont believe me just try it yoursel

I have. If for example when the bed is too close I get an elephant foot on the bottom layer. By the 3rd layer there is no difference with the 4th layer.

The bottom of the nozzle has a flat "shoulder" area around the hole. It spreads out the currently printing layer like a knife spreading butter on toast. Or frosting on cake.

 

[tsagos 8]

The elephant foot.... Is somehow intergrated in cura so we get better bed adhesion, right?

Is there a way that we can minimize or get rid of this setting?

 

[yellowshark 153]

No I do not think so. If it is important dimensionally I remove .1mm all-round from the base layer during design modelling

 

[nallath 1,120]

Cura over extrudes the first layer (thats the initial layer thickness setting). This causes the elephant foot. Decreasing this value means that you have to level the bed a lot better.

 

[yellowshark 153]

Looks like I stand corrected Why does it do that Nallath? It causes problems for users and with, it seems to me, a questionable benefit.

 

[tsagos 8]

thanks Nalath! i will start tests next week!

I guess its a better way to test bed leveling too?

 

[nallath 1,120]

If you don't over extrude on the first layer, you will need to level the bed -exactly- at your layer height. Which is very hard to do.

We try to set the basic settings in such a way that the chance of print failure is as low as possible (which has a negative impact on how it looks in some cases). But we know that we don't get things right and will most likely be wrong in some areas, thats why we allow you to edit almost any setting. Even change them to a number that does not make sense to us (Cura will only highligh the value as being red, it will still try do whatever you told it to do!)

You can change the first layer thickness to a lower number if you're feeling experimental. I know of a few experienced users that set it to 0.2 (or even 0.1 if you're feeling very ambitious!). If you get good results, share them. If you find a fix that consistantly improves our settings, share it. If you can prove that this improves on our settings, we're more than happy to change them in the main application.

 

[gr5 2,167]

I almost always print .3mm bottom layer but on occasion I have printed .1mm bottom layer. Levelling must be done by trial and error by printing "brim" or "skirt" and adjusting the 3 screws on the fly, halting print, starting over. Repeat a few times until perfect. Here is an example print with red pla at .1mm:

 

[gr5 2,167]

"elephant foot" is a term that means different things to different people. 2 different phenomena that I know of. One is the bottom most layer sticking out - this is caused by imperfect leveling. It can happen with .3mm layer, it can happen with .1 bottom layer.

The other issue is a inward curving of the layers *just above* the bottom few layers. Especially on corners. This *also* looks like elephant foot and is a problem with layers *just above* the bottom layer being too small (versus bottom layer being too thick). This second issue is usually caused by heated beds above 60C or 70C. I now usually print PLA on 50C heated bed.

Photo of these second type of "elephant foot" is here (5th photo down on left column):

http://support.3dverkstan.se/article/23-a-visual-ultimaker-troubleshooting-guide

 

 

[gr5 2,167]

I suppose a 3rd type of "elephant foot" would be caused by having the bottom layer be .3mm but subsequent layers .1mm if the part is supposed to tilt. Cura slices slopes into a staircase pattern and if the bottom layer is .3mm and remaining layers are .1mm and the wall is sloped then you can visually see the thicker layer. This is as expected. As designed. It's damn hard to get leveling better than 50 microns so having the bottom layer be 300 microns makes it easier to get good prints. But I have my bed leveled closer to 30 microns now so 100 micron bottom layer works for the most part.

It's hard to get better than 30 microns because the glass can be bent by screws and clips and such and the overhead gantry isn't perfect (the 4 rods that move the gantry aren't all parallel within 30 microns! Errors are a little higher than that I think). So I can get better than 30 microns for a small area of the print bed but across the entire print bed would be harder.

 

[yellowshark 153]

Thanks Nallath I can see where you are coming from. I have never used flow % but I assume I can mitigate against the way Cura does it by reducing the flow for the 1^st layer. It will take some trial and error – or are you able to establish how much Cura over extrudes – but no doubt I can get there. Hi George, Nallath’s comments methinks make it four ways to get an elephants foot.

And LOl we all use different methods. For nozzle to bed distance I use a digital method. I take a cube, change the z height to 1^st layer height and often just double the x/y plane dimension. I print, in the centre of the bed, and then use a binary chop process; I add 50 microns to my z-offset and print and then subtract 50 microns from my z-offset and print. Then I compare the 3 prints. If subtracting 50 microns gives the best result I will subtract another 50 microns and print again. And I continue doing it until subtracting 50 microns gives a poorer result. That therefore then gives me a 50 micron range, say 150(better than 100) - 200(worse than150). I then add or subtract 25 microns and just keep repeating the binary chop until I can see no difference.

If I know I am going to print something with a big base I will still follow this process.

Then I will increase the x/y dimension of the "cube"up towards max. bed dimensions and print. I then use the bed levelling screws to adjust for a non-level as required.