Spurious supports - why are they generated? - how to get rid of them?

[Flying_Roger 1]

In several models, I got spurious supports generated by CURA 4.8.0
By "spurious", I mean that these supports does not seem to support anything.

 

I tried to get rid of them using the "support blocker" tool, but to no avail.
As the support blocker acts on the model, not on the cura engine, you cannot select a support for deletion: instead, you need to mark the area that triggered the support.
However, how can I do that for supports that do not support anything? It is hard to figure out which area of the model triggered them...

 

Here attached an example, generated with the parameter "support angle = 55°".

On the last picture, you see that a support is "hanging in the void" almost without any contact with the structure.

I appreciate CURA, but I have only a few months 3D printing experience, so sorry in advance in case I missed some basic knowledge.

   

Edited January 31, 2021 by Flying_Roger

[fvrmr 73]

Do you need everywhere support? Because you can change support placement to touching buildplate. With the option everywhere it will also print support on the model. 

[GregValiant 1,251]

They aren't there to support that radius feature because it is more than 55°.  My guess (since they are rectangular) is that they are attempting to support the rectangle above.  Moving the support blocker up higher might help.

[Flying_Roger 1]

Thank you for your replies, but:

- I need to support everywhere because there his a horizontal cylinder hole higher in the object and it needs internal support.

- How can the "unwanted" support support something that it does not touch??? 
- I tried to use the support blocker, but it is very hard to use because it works indirectly instead of simply clicking on the support that you would like to delete.
The only way I found was to set the angle to 75°, but I wonder whether the cylinder hole will be printed correctly, and it is only at the end of a long print that I will figure out...
 

[DivingDuck 104]

@Flying_Roger, a little bit to late, but maybe helpful. There is a setting that forces this problem sometimes for some of my models: Support ->Use Towers

If this is activated try with uncheck it for this model.

[Flying_Roger 1]

Hi DivingDuck.
I presume that you refer to what is called "Support structure = Arborescende" in French.
(I have the French version of Cura).

 

Indeed, this setting produces very strange supports and I never use it.

 

In the case that I reported, the only way to get rid of all the unwanted (an obviously unuseful) supports is to set the maximum angle to 75°.
However, i am afraid that my printer will not be able to bridge correctly at 75°.

I am now trying and old version of Cura (15.04.6): this version is a bit limited, but at least, it does not generate supports hanging in the void, even with angle=60°. 

[GregValiant 1,251]

I did a bit of a test for "support angle".  With a 0.4 line width and 0.2 layer height, the maximum theoretical angle is 63°.  There is enough "stickiness" to the filament that 65° printed well.  An unsupported 70° surface printed, but drooped as the outside loop was printing over air.  It might be acceptable on a gusset but not for any more important feature of a part.

 

Did you try a support blocker for that rectangular feature that is surrounded by the radiused feature?  It only needs to be 1mm thick and located correctly to negate those "hanging" supports.  That shouldn't affect what is above and your hole should still have support in it.

 

 

 

[DivingDuck 104]

2 hours ago, Flying_Roger said:

Hi DivingDuck.
I presume that you refer to what is called "Support structure = Arborescende" in French.

 

Hi @Flying_Roger,

No, this is Tree support (I guess). It should be something like "utiliser la tour" (Google translation)

 

The one I mean is, if you have activate Support with Structure = Normal (pic CuraSupportOn) and then go the entries for support down to the end you will find an entry called "Use Towers". This is activated by default (pic CuraUseTowersOff). Deactivate this and see if this will improve your slicing.

 

It is maybe possible that you don't see this entry. Activate show all settings on the right of the search bar.

 

And as @GregValiant already mentioned, an angle >65° is quite challenging. Don't think, this will work good, but try it and let us know your experiences. I'm interested to see how it will look with your printer.

 

[Flying_Roger 1]

Thank you very much for this solution.
There is indeed a parameter "utilisation de tours", and unchecking it prevents CURA to add those strange external supports.