How to stop Prusa Slicer cutting out of lower layers
 

How to stop Prusa Slicer cutting out of lower layers  

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xavierx
(@xavierx)
Active Member

Firstly imagine you print a normal rectangle.

When the printer is printing the top layer, it will do a full rectilinear surface from one side to the other and it will look perfect.

Now imagine you have a rectangle with a word on top (first example image) 

If you just print it as is, then the top surface of the box is a mess with stripes as the printer will try to print around the letters, even though the letters are not actually in the box, they are on top of the box. 

Now if we move the layer slider down to the last layer of the top of the box, we can see that it has carved out the word "Test" in the top of the box. I do not want this. I want to the top surface of the box to be flat, because I want to avoid the banding stripes where it prints around the word.

So I thought I would try the height range modifier and set it from 9-10mm (the last 1mm of the box) and then set the infill to 100% for that modifier. This does not work as I expected, and you can still see the word "Test" carved out even though it should be a 100% filled layer. (see 3rd image)

Does anyone know why it is doing this and how I can fix it? 

The way that it is sliced appears to be Prusa Slicer specific, as results are different when I did a quick check in Cura and Simplify3d (as well as a couple of STL viewers) so I don't think it is a problem with the model (which is from Fusion 360 by the way) 

Thankyou for helping

This topic was modified 1 month ago 3 times by xavierx
Posted : 20/06/2020 3:38 pm
Neophyl
(@neophyl)
Noble Member

Please attach a copy of your project file. The forum will only accept limited file types so you will need to zip it up first to attach it. 

There are so many settings and variables that the 3mf project file is the best way to run through multiple options and allow us to see what is going on as not only does it contain the model but also all your printer settings too. 

Posted : 20/06/2020 3:56 pm
xavierx
(@xavierx)
Active Member

No problem, I have included the stl and the 3mf

Thankyou for helping

Posted : 20/06/2020 4:33 pm
Neophyl
(@neophyl)
Noble Member

Ok, I see what you are trying to combat.  I dimly recall it used to do something like that all the time ages ago which was a bug, basically when you print on the smooth layers it makes for a weak join so it was changed to allow the infill to come up through the area.  In your case though that's not really an issue and is what you want.

Tried all the usual suspects but I just couldn't get it to do what you want at first.  I have attached a modified version of your project that does it though.  I'm still not 100% sure why the combination of no top/bottom layers with the 100% infill works when the other don't though.  Also note that the first layer over the infill is not being classed as bridging which *may* cause print issues as it wont be using bridging speed or flow but for this instance I don't think it will.  Unfortunately my printer is busy so I can't print to test that.

Hopefully the attached will work for you.

Posted : 20/06/2020 5:31 pm
xavierx
(@xavierx)
Active Member

Unfortunately I am unable to open your file (Prusa Slicer 2.2.0) 

 

I get the attached error

Posted : 20/06/2020 7:50 pm
Neophyl
(@neophyl)
Noble Member

Ah, sorry, I was using the 2.3.0-alpha build. Didn’t realise that it wasn’t compatible with the current 2.2.0 release. 
let me redo what I did in 2.2

Posted : 20/06/2020 7:58 pm
Neophyl
(@neophyl)
Noble Member

Here it is in v2.2.0 

Posted : 20/06/2020 8:04 pm
xavierx
(@xavierx)
Active Member

Well I have to thank you for your efforts, it does at least look like you might have solved it. I will have to give it a test print later. 

Just to confirm, what you did different was to add a modifier to set the top and bottom layers to zero on the 9-10mm range? 

I have no idea how you worked that out 🤣 

Posted : 20/06/2020 8:09 pm
xavierx
(@xavierx)
Active Member

Thankyou for your help. I did a test print

Your workaround works for me, but as you say, it doesn't do the bridging layer over infill so you can't use it with low density infills. 

Do you know the best way to get the attention of the Prusa Slicer developers to ask if this can be allowed as a slicer setting again. I notice that files sliced only a few months ago print with nice flat surfaces as intended, but definitely not in the current version of the slicer 

Posted : 24/06/2020 5:04 pm
Neophyl
(@neophyl)
Noble Member

The best and pretty much the only way is to raise an issue on the Prusa Slicer github page here https://github.com/prusa3d/PrusaSlicer/issues  
I’d include all the pertinent information along with your original 3mf file and images so they can see exactly what your issue is.   They will ask for the 3mf anyway if you don’t include it 😀

 

Posted : 24/06/2020 7:38 pm
xavierx
(@xavierx)
Active Member

I posted an issue a few days ago but its not been noticed 

https://github.com/prusa3d/PrusaSlicer/issues/4437

 

The workaround posted above introduces a new issue, with large objects, when it starts printing the upper layers of the box, it causes warping. I assume this is because it is not properly printing the bridging over the infill and is printing too fast? 

Posted : 06/07/2020 2:45 pm
Neophyl
(@neophyl)
Noble Member

Not sure , without actually printing something that shows the new problem.  Theres another issue with first layer printing over infill as thats treated as bridging which is also causing some issues from what I recall.  It could be that you are running into that one too.

Github issues could take years to be fixed.  There's over 1400 of them after all.  Depends on how serious it is, how many people are actually having the issue and how vocal they are about it.  Also if its a one line fix then I suppose that might make it in a release sooner, although even one line fixes can take significant testing resource to make sure the fix doesnt introduce other issues so its not that straight forward.

Posted : 06/07/2020 3:07 pm
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