Supports on top of model  

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g monkey
(@g-monkey)
Eminent Member

I have had this problem in the past with other prints, but this print is suffering from a great deal of support material going straight through the model onto the top side, where it doesn't belong.  Does anyone know what causes this and/or how to get rid of it?

This happens with both 2.2 and the 2.3 release.

Many thanks

R

This topic was modified 2 months ago 2 times by g monkey
Posted : 13/12/2020 7:38 pm
fuchsr
(@fuchsr)
Reputable Member

Welcome to the world of Prusaslice's; aggressive supports! 

 

Here are some settings floating around on this forum that have made a real difference for me but still, plenty of models for which PrusaSlicer is just going bonkers.

Also, with the new version you can "paint" supports onto your model, so you have more control but it hasn't really changed the underlying algorithm as far as I can tell.

 

Support settings:

0.25mm z distance.
75% xy distance.
3mm support spacing.
4 interface layers.
0.2mm interface layer spacing.

 

Posted : 13/12/2020 8:40 pm
g monkey
(@g-monkey)
Eminent Member

@fuchsr  thanks, but if you look at the file these are (more or less) the settings that I am using.  Also, simply removing the supports doesn’t really help as some support will clearly be required.  Any other ideas?

Posted : 13/12/2020 10:57 pm
fuchsr
(@fuchsr)
Reputable Member

@g-monkey

Not from me. I’ve never found a way to avoid those artifacts. 

I know some of the folks here would suggest  trying a different slicer...

Posted : 13/12/2020 11:51 pm
towlerg
(@towlerg)
Prominent Member

Have a look at support blockers.

Posted : 14/12/2020 8:34 am
Neophyl
(@neophyl)
Noble Member

Best I could do was this -

 

 

Even that has some parts over the top so its not great.

I also made a few other changes to the project settings so have a look at the attached project.  I noticed that without detect thin walls half of the object doesnt print and with thin walls =on the top has a discontinuity in the slice that would likely lead to a weak area or a change in appearance.  To counter that I added a 0.1 xy offset and turned the detect thin walls =off.

Also with the curve on the bottom edge It needed to be raised slightly to get any sort of contact with the bed.  Normally I wouldnt use a raft as with the adhesion on prusa bed there is little need and it usually makes things worse but in this case it was needed to get it correct, even using a brim.

Anyway, that's how I would print it if I had to.

Posted : 14/12/2020 9:00 am
g monkey
(@g-monkey)
Eminent Member

@towlerg  - I have tried painting on support blockers on the top using 2.3 but this has no apparent effect, probably because the supports are coming from below the print.

@neophyl  - thanks for this, I will have a look.  The fundamental problem of support material going through the print onto the top side looks like a bug to me, unless I am doing something wrong.  I have tried several orientations and it happens in all of the cases that I tried.  Like I say too, this is not the only print where I have had this issue.

Posted : 14/12/2020 9:08 am
fuchsr
(@fuchsr)
Reputable Member

@towlerg

This may be a common misperception of how support blockers work. Took me a while to wrap my head around it as it's a bit counter-intuitive. Most normal people would assume positioning a support blocker means "do not put a support here". But they don't literally block supports just in the location they are positioned. They block supports to the region they're intercepting with. So it's all or nothing. If a support is printed, it is printed in whatever mysterious way PrusaSlicer decides it should be printed, and you can't block just parts of it (like the stuff printed on top) with a support blocker. 

This post was modified 2 months ago by fuchsr
Posted : 14/12/2020 11:56 am
g monkey
(@g-monkey)
Eminent Member

I have not played with the xy size compensation parameter before, so I'll look into this as I have several thin prints to do which this might help with.  I have certainly had problems with artefacts before when 'detect thin walls' is switched on.

Posted : 14/12/2020 1:19 pm
towlerg
(@towlerg)
Prominent Member

@g-monkey

Is this what you're looking for. I assume you want to support the tip and some support around the base to stop it falling over.

BTW are any of the edges on your model straight lines? If so, perhaps there's a better orientation.

BTW the support you were seeing isn't going through the blade, you can see that using the height slider. In default mode the top of support is square, parallel to the bed.

This post was modified 2 months ago 3 times by towlerg
Posted : 14/12/2020 2:26 pm
g monkey
(@g-monkey)
Eminent Member

What neophyl came up with looks like it should print fairly well.  I'll play with the xy parameter on some other thin wall prints as I have had issues with the 'detect thin walls' generating artefacts before. 

However, I still don't understand why the supports are basically going right through the print to the top side, what causes this and how to avoid it - as I say, I have seen this on other prints.  Some of the edges on this model are straight lines (if you are looking in the right plane).

Posted : 14/12/2020 2:35 pm
towlerg
(@towlerg)
Prominent Member

@g-monkey

"However, I still don't understand why the supports are basically going right through the print to the top side".

"BTW the support you were seeing isn't going through the blade, you can see that using the height slider. In default mode the top of support is square, parallel to the bed."

Posted : 14/12/2020 7:08 pm
g monkey
(@g-monkey)
Eminent Member

@towlerg I suggest you actually look at either my zip file or neophyl’s.  The supports do indeed go through the part.  You can run either file in PS and clearly see that.

Posted : 14/12/2020 8:07 pm
Neophyl
(@neophyl)
Noble Member

I think what you have is a difference in terminology.  Supports are placed on TOP of the part, above where the lower support is placed, in error (its definitely an issue).  However the support doesn't physically go THROUGH the part.  The layer preview you wont see any of the light green actually inside or going through the part perimeters.

Posted : 14/12/2020 8:15 pm
Neophyl
(@neophyl)
Noble Member

Damn, ran out of edit time.  Had another go now I'm at home.  Came up with this

If I didn't have some Mandalorian hand plates printing on the cr10 I'd give it a go as its a pretty short print with a 0.6mm nozzle.

The project has my mk3 but you can just change the printer to yours and dont forget to add in the 0.1 x/y compensation when using thin wall=off

This post was modified 2 months ago 2 times by Neophyl
Posted : 14/12/2020 8:27 pm
DarcShadow
(@darcshadow)
Trusted Member

Have you considered rotating the part? If you lay it down so it's kind of a bowl and set the overhang threshold to 30 it'll slice with the supports only on the bottom and greatly reduce the amount of support structure. The object might be too thin to print this way though, but looks like it'd be worth trying.

This post was modified 2 months ago by DarcShadow
Posted : 14/12/2020 8:28 pm
g monkey
(@g-monkey)
Eminent Member

Thanks all.  Yes, I mean it looks like a bug to have supports on top of the part.  Any idea why this happens?

Posted : 14/12/2020 8:59 pm
g monkey
(@g-monkey)
Eminent Member
Posted by: @darcshadow

Have you considered rotating the part? If you lay it down so it's kind of a bowl and set the overhang threshold to 30 it'll slice with the supports only on the bottom and greatly reduce the amount of support structure. The object might be too thin to print this way though, but looks like it'd be worth trying.

Hi @darcshadow, for this part I am trying not to align the major curvature with the x-y plane as I find it doesn't print so well.  Another way of saying this is I'd rather have the smaller radius be projected onto the x-y plane so that it is smoother.  It is a bit difficult with this piece as it curves both ways.  I'm still not sure what triggers the supports to appear on top.

Posted : 15/12/2020 10:14 am
g monkey
(@g-monkey)
Eminent Member

Interesting and following that train of thought, I rotated the model so that the overhangs were minimised on the upper bits and got this, so that there are only supports on the bottom part.  I'm not near my printer but am curious to see how well it prints!

 

 

Posted : 15/12/2020 12:04 pm
Neophyl
(@neophyl)
Noble Member

That's basically what I did in the second one posted above.  I did do a print with it last night.  I found that in the middle the layers were not well bonded (at just above the level where the support stops).  That may be down to I was printing too fast though for a thin print like this though.  

Posted : 15/12/2020 12:09 pm
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