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I'm trying to print this model of a boat:

enter image description here

It has 2 keels joined by 5 bridges, but the top of each keel is curved, so while the middle part is mostly flat, the bridge on the back has a bit of a slope (as you can see with the "stair" effect).

The problem I have is that I can't get Cura to properly bridge that specific part: It creates a bridge for the first layer, but on the next layer (where there's a part that needs bridging), it just starts drawing a surface:

enter image description here

In this picture you can see layer 86 it has drawn a bridge between both keels, but on layer 87 it tries to print a surface larger than posible. That results in this happening:

enter image description here

and this causes big gaps in the top surface.

I've been trying to play a bit with the settings in Cura, but I can't find anything that would fix this... Is there anything that can help me? (maybe even the model has a design problem)

0scar
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Victor Oliva
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    Those are very long bridges. I would use a very sparse support for these, like 5-10 % or such. To reduce support to a minimum, I'd also print the whole model upside-down, – Trish Feb 09 '20 at 18:31
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    @Trish: If using low support infill rate, I'd definitely recommend using a support interface (roof). Otherwise you're likely to get non-bonding of consecutive extrusions, even if they don't sag much, which will look really ugly as a top surface and might "unravel" over time. – R.. GitHub STOP HELPING ICE Feb 09 '20 at 21:34

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Cura has some options in this area that might or might not help. I've had mixed results. You should make sure Enable Bridge Settings is on, and try adjusting Bridge Skin Support Threshold. By default bridge settings are only used if 50% or more of the area is unsupported. Area is an utterly ridiculous/meaningless metric for whether bridging is needed, so you probably need to set this to just a really high value like 90% or 95%. You may also want to check that Bridge Has Multiple Layers is on.

With that said, for your model I would just use supports with a support interface (roof) below the bridges. You could reduce the material cost of them with Support Tree mode. But there are of course places where you can't use supports in similar models (bridge is over another part of the model and there's no access to remove the support material), so having working bridge settings is still desirable.

R.. GitHub STOP HELPING ICE
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  • One other thought, but I'm not sure if it's good: you might try reducing Extra Skin Wall Count to 0 so that Cura's not trying to build inner walls over thin air. – R.. GitHub STOP HELPING ICE Feb 10 '20 at 04:42
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    The key was on Skin Support Threshold - In my case 80% was enough, thanks for the tip!. I don't think I'll be using supports.... it's a 3cm gap and although it's true that's starting to be a long bridge, I see that for the ones that printed properly there's a minimal amount of sagging. – Victor Oliva Feb 10 '20 at 07:22