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Bulging corners. How to make them not do this?


tisimst

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Posted · Bulging corners. How to make them not do this?

When I print a corners that approach 90 degrees or are more acute, I get some annoying bulging going on at the corner. See the attached picture for the illustration. Any setting that can help control this? I would gladly live with rounded corners if at least the face remained flat. And of course I know I can manually add rounds to my models, but when I am printing something off of Thingiverse (for example), they all have sharp corners and I can't change that. Any suggestions for me?

 

I'm using the latest Cura (5.1.0) and I'm printing in PLA on an Anycubic Chiron. Thank you!

bulging-corners-problem.png

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    Posted · Bulging corners. How to make them not do this?

    Generally, higher acceleration numbers will give better corners.  At 1800 they should be crisp, but your Jerk settings at 8 may be too low.  Jerk is in mm/sec and if you think of it as "minimum speed around a corner" you can see that your slowing down a lot before changing directions.  Those rounded areas may be blobs.

    Leave the Accel at 1800 but move the Jerk up to 20.  It shouldn't take but a few layers to see if there is any improvement.

    I agree that the problem is in the Accel and Jerk settings.  It may take some experimenting to find the sweet spot where the proper combination yields good results.

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    Posted · Bulging corners. How to make them not do this?

    Much appreciated. These values I show are the stock settings for the Normal-0.2mm settings that come with Cura. I will definitely give that a try, though, and let you know how it turns out!

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    Posted · Bulging corners. How to make them not do this?

    Surprisingly, bumping to 20 didn't help. It actually ended up causing quite a bit more "ringing" instead. It definitely helped in some ways, though. Any other thoughts?

     

    Here's a before/after pic:

    before-after-jerk-8-to-20.jpg

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    Posted · Bulging corners. How to make them not do this?

    Try to equalize the all speed settings (inner wall, outer wall, ....) and also jerk.

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    Posted · Bulging corners. How to make them not do this?

    Thanks, @Smithy. Will give that a try and report back!

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    Posted · Bulging corners. How to make them not do this?

    Hi @tisimst, this bulging on corners versus ringing is an annoying issue that we are often dealing with as well. The major issue is that the extrusion is not starting and stopping in the same timescale as the motion does. This basically means that, even with a direct drive extruder, your flow will not slow down enough in comparison to the movement of the printhead. This leads to blobs on corners: material is still coming out on roughly the same flowrate, while the printhead almost ('jerk' = 8mm/s) stops. I'm writing 'jerk' as marlin jerk is not the derivative of the acceleration.

     

    This problem can be overcome by setting the 'jerk' closer to your print speed, this way your extrusion and motion stay synchronized -> both will stay constant. The problem then is that you are taking corners at a constant (printing) speed, this leads to ringing even at moderate speeds (25mm/s+). So if you want no bulges and no ringing, productivity will take a significant hit. An other setting that reduces bulging is reducing the layer height (less room for material to creep out in the corners), but again this is a productivity hit.

     

    A third thing that does not necessarily hurt productivity is to print the outer walls first: this way the bulges formed on the inner walls do not propagate to the outer wall. This will reduce bulging but bulging on the outer wall still happens.

     

    Ideally you would want to use a control feature that synchronizes flowrate with your motion movement, this is unfortunately not possible with Cura. I think newer Marlin versions do support these kind of control features.

    I always chose which hit I take: If I want dimensional accuracy I will print with a high jerk and have ringing (ringing does not lead to large dimensional errors). If I want a nice looking print I will find a balance between bulging and productivity loss.

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    Posted · Bulging corners. How to make them not do this?

    I really appreciate all those thoughts, @TomHeij. That makes total sense. For me, cosmetic will generally be less important than precision. And as much as I'd like to print quickly, I'd be ok with longer prints knowing they are going to come out right. Will definitely have to try out your suggestions to see if I can work out my issue.

     

    My applications will almost be exclusively mechanical components, so I'm grateful for any and all tips from folks like you who have been doing this longer than I have.

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