SOLVED Cura Slices Blobby & Disconnected on Top Layer?

[KiRAWRa 1]

Hello! I'm having an issue with the top layer of slices in Cura. Even though my model is supposed to be flat on top, the slices form globby, uneven layers. I hope the pictures do a good job of showing the problem.

 

I am very new to Cura and 3D printing in general. I have had my printer since yesterday, and only downloaded Cura today. I printed some items from Thingiverse (a Chess Rook, a Benchy, and a Companion Cube) and they all came out fantastic. I read that Cura can import PNGs/illustrations, so I wanted to try making a little stencil thing from my logo. (I am a digital artist so 2D drawings are my area of expertise - I have zero experience in 3D programs or modeling.)

 

I made my design gray with a white outline for a raised edge. Cura imported and modeled it perfectly, just how I wanted it to look!
Unfortunately, the slicing doesn't seem to play nice with it. The model looks perfectly flat to me, but the topmost slices are filled in very unevenly. I printed it anyway just to see, and the whole thing looks great right up until the final top two layers which print weird and blobby just like in the slice preview.

 

I feel like there is probably a very simple solution to this, but suffice to say I don't really have any clue what I'm doing, lol. I've tried googling for answers, and I have seen others mention slicing issues, but given how new I am to this craft, I really don't know the proper terminology or key words for what is happening here or how to fix it.

Thank you for your time!

[kmanstudios 1,120]

I would first assume that there is a difference in colours not perceptible by the naked eye. Was this made with a vector program or bitmap program?

[KiRAWRa 1]

The logo was drawn in Photoshop CC. The white outlines, specifically the areas that are causing me trouble, were made with a "stroke" function which automatically outlines the image in a solid color of your choosing. There really isn't any opportunity there for variables like accidental transparency or color change, since it's just a solid autofill function (as in: no human involvement that could influence how well those lines were drawn). 

Just to be super sure though, I doubled up on those layers and went over them again with a solid color (just in case there actually was any variance of transparency or hue) and am unfortunately still encountering the same problem. 

Also just as a note - if there were issues like that with the image, wouldn't those abnormalities be visible in the model? My model actually looks great (no bumps, no gaps), and the issue only seems to appear in the slices. 

Edited February 28, 2021 by KiRAWRa

[gr5 2,176]

I would just hand edit the gcode to remove the top two layers.  Just literally cut them out.  Each layer is labelled in comments in the gcode file so it's easy to find every layer.  You can search for the letter Z which will likely appear quite a bit in the first 30 lines of code but then only once per layer (unless you have zhop enalbed which hopefully not).  

 

It's almost certainly a "brightness" issue as kman says.

[KiRAWRa 1]

Deleting the top two layers in GCode really improved it! The slices still kinda want to put tiny bits and blobs here and there, but it's quite visibly much better than it was before. 

 

I'm afraid I still don't quite understand what is meant by "a brightness issue", since it seems to me that if this were being caused by variances in my source PNG, those abnormalities would show up in my 3D model as well. But you can see in my screenshots that the model is nice and flat and smooth. These blobs and holes in the layers are only showing up in the slices, which doesn't seem to be registering the complete height of the walls, even though they're clearly visible in the model.

 

I decided to test this with another design of mine - one with even thinner walls. Once again, the model shows up fantastic, but the slices are kind of a disaster. It appears Cura is inclined to just ignore parts of a model that it deems "too thin"?

For reference, I am using a .4mm nozzle. I tested slicing with a .2mm nozzle and the detail improved somewhat (just fiddling with settings here). 
Is there any way to tell Cura to print all parts of the model, even if it thinks some areas are too thin? I really don't like it ignoring details of the model*. I tried the "print thin walls" option and the difference was minimal.

*Granted I realize this is probably a QOL feature to prevent making real messes of things that would be too small or close together, but in the case of my little stencil here, those walls are fine and I wish I could tell Cura to just print it anyway.

 

I was really hoping to be able to make a bunch of these cute little stencils from my art, but if it requires manually deleting the top layers of the GCode for each one or barely registering the detail in general, I'm not sure it's worth the hassle.

[kmanstudios 1,120]

I am not sure what the bottom image is...sorry.

 

But I can (hopefully not confuse you) with the brightness issues.

 

It has to do with antialiasing and such. All the image has to do is have a few pixels that are not the same value to make the levels not smooth. You may not see it, but it can be in there.

 

As for thin walls, yes, Cura can only slice for print down to a certain thickness. Try turning on 'print thin walls.' Or just make the image a tiny bit thick in those thin wall areas so Cura can see it for your nozzle size.

[gr5 2,176]

He already tried "print thin walls".

 

I'd try a higher resolution image.  Make sure there are at least 5 pixels across on the walls.  Even if that means a lot more pixels.

[gr5 2,176]

Then I'd play with line width.

[KiRAWRa 1]

Ah okay, after much trial and error, I see what is meant by the issue with antialiasing. I originally thought this was in reference to the top of the model not being flat due to inconsistencies somewhere in the infill, but now I understand you were talking about the very outside edges of the lines/walls.

For anyone following along that may be running into the same issue:
Antialiasing was causing a slight inward taper to the 3D shape of the walls. So the bottom slices looked fine, but the taller the walls, the more splotchy the slice layers became as the wall thickness shrunk slightly narrower than it could register. For clarity - this is the part that kept confusing me. I didn't understand why most of the slices on the lower parts of the model were fine, but the top ones seemed to become arbitrarily crummy.

After I removed all the antialiasing and made the image completely solid down to every pixel, the slices were solid and consistent all the way to the top layer, hooray! 

For the most part, this fixes my initial problem. I just have to make sure the line art in my drawings make a thick enough wall, and remove all of the antialiasing to maintain consistency all the way to the top of the model. 
 

However, the slices (and printing) were still perceptibly wobbly. The other models I have downloaded and printed, specifically a little crown whose smallest point was set to the exact same width as my logo (.4mm), came out perfectly straight and crisp. For as awesome and convenient as height mapping an imported PNG is, I see there still remains a limit to what you can get out of something made from pixels (especially when you are printing this small).

Time to use vectors I guess!
I imported the PNG into Inkscape, traced and exported it as a vector (.svg), imported the vector into Fusion 360 and modeled it into the 3D stencil, and then finally brought that new model into Cura to slice. This made a significant improvement compared to the Cura height map version (which you can see compared in the attached screenshots)! Unfortunately it's a bit more work than I initially expected, but I've finally achieved the result I wanted.

 

Thanks muchly for the responses, I honestly expected people wouldn't even bother with my noobishness. I'll mark this as solved, please enjoy a picture of the little cat face logo army I unintentionally created through troubleshooting. 👍

[kmanstudios 1,120]

3 hours ago, KiRAWRa said:

After I removed all the antialiasing and made the image completely solid down to every pixel, the slices were solid and consistent all the way to the top layer, hooray! 

Awesome! 👍

 

3 hours ago, KiRAWRa said:

noobishness.

That has been all of us at our starting points. 🙂

I used to post under the nom de plume "The clumsy noob" complete with pics of burned fingers and other things. And, when I had to sign things, I would use my plume de nom. 😜 These days I am more of "The forgetful dood."

You will be surprised how fast you can get through this in the future. It is a bit of an upward slope at first, but it all starts to come together.

 

3 hours ago, KiRAWRa said:

Time to use vectors I guess!

Not really.....you can try using bitmap (2 bit black and white) as well as 256 for this if you want to cut down on the anti aliasing. Also, keep in mind that the technique you started with is very good as producing (purposeful) rounding when using a full 24 bit image. Kinda like planographs (is that the right word?) NO!! Lithoplanes.... duh..... sometimes, searching for the right words is a bit like bobbing for apples. 😂

 

Another thing to consider is exporting the model from Cura to a mesh format and then import that into a modeling program that deals with mesh and just manipulate from there.