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Liam

Adaptive Cura Idea

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Everybody's printer completes overhangs and bridges with varying levels of success and the current settings available in Cura make it difficult to recognize this. What if, after your printer finished a print, you could go back in Cura and highlight problem areas on the model so that these types of areas would be more likely to receive support or other 'help?' Just an idea.

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Hey @nallath,

Food for thought here...

Do you think a speed reduction on shell thickness based on overhang would be easier to implement as a general behavior?

ex:

Speed % on high overhang: 50%

minimum overhang slope before speed reduction: 30°

maximum overhang slope: 60°

ease in/out distance: 10mm

So speed could reduce progressively when getting near an overhang > 30° and reach full reduction at 60° and up.

Edited by Guest
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Liam's original idea has been brought up more often: To be able to point in the interface where support is built. It's very involved to implement though.

pm_dude's idea is certainly technically feasible. Since CuraEngine is inherently 2D (per layer), it would offset the layer below with a certain distance depending on the layer height and the required 30° of overhang. It subtracts those areas from the current layer's area. The result is the areas that would have to be printed more slowly. This is already currently used to detect bridges. The lines in bridges are currently oriented to provide maximum strength (so lines don't have endpoints in the air).

To make it print progressively slower between 30° and 60° is difficult due to the way g-code works.

I'll make an issue for our internal issue tracker. It'll be "nice to have" though, so don't expect a feature such as this to come in anytime soon. Maybe it'll get shot down too.

Edited by Guest

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I wonder whether going slower will actually increase the quality, given the hysteresis effect of a Bowden tube might cause overextrusion and under extrusion around speed changes.

Moreover, problems of overhangs are foremost the sagging and falling off material, which I expect to be more of a problem at slower speeds.

Have you tried turning the speed down by hand during the printing of overhangs? Before implementing such an idea it's good to have some empirical verification of the idea.

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@bagel-orb What do you mean by "Hysteresis effect of a  Bowden tube".  Are you referring to the delay between the feeder push and the extrusion time? If that's the case then that issue would occur everywhere due to acceleration in general.

I always had the impression that steep overhang printed better at slower speed. More so with  bridging. Yes sagging and falling is made worst because it give more time to fall but it also reduce occurrence of breaking the filament.

Maybe my perception is biased because printing slower allow you to print colder (in general) which definitely help with overhang and bridging and that would not be doable with what I'm proposing.

Edited by Guest

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@pm_dude indeed many people see the hysteresis effect as a delay, which is actually an oversimplification of what is happening.

The fact is that a given speed requires a certain pressure in the nozzle, which translates to an offset of the filament. Higher speed = higher pressure = higher E values.

The effect does take place between every two extrusion moves (if they have an angle other than straight). However, once filament has been put down in a certain place, the pressure increases. This constitutes a self regulating mechanism: as long as the pressure in the nozzle is high enough to obtain the maximum flow required in a single extrusion move the layer below will provide counter pressure at the corners, where the movement speed and the filament flow slow down.

When changing the speeds in the gcode, the maximum flow over line segments changes between consecutive segments, which causes the pressure to be too low, which in turn causes under extrusion until the pressure is high enough again.

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I just recently printed a bowl where the geometry of the lip was such that it would have been impossible to print it like a dome shape with the bowl upside down. The bottom of the bowl sagged into the support while printing and print quality was reduced. Would there be a way so that the squares in the mesh of the supports would get smaller as it got closer to the print so that the holes that were being bridged weren't as big? Would this save print time and material usage?

Edited by Guest

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There's a support roof which you can set to have a higher density.

There is no possibility to make a fluent change from less dense to more dense; there's just two states: less dense (support 'infill') and dense (support roof).

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There's a support roof which you can set to have a higher density.

There is no possibility to make a fluent change from less dense to more dense; there's just two states: less dense (support 'infill') and dense (support roof).

 

What do you mean by support roof? Is there a way to put a flat surface on top of the support to make the print not droop inside of the squares?

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Yes

 

How?

 

Cura 1.99 has this option. You have to turn on the option under in the settings for support and select support roof. You will then be able to adjust the roof percentage.

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