Can some one help me understand why I am getting these ugly diagonal lines on the top layer?
This is a new issue for me and I am not sure what is set wrong.
I tired turning on “Avoid Crossing Walls”, but it didn’t seem to make a difference.
I don’t even see matching travel lines…
Hi @Lexi ,
I wish I was able to do so focussed and complete problem description 
I have not used the archimedal top surface myself but expect that this is the main cause. At least I have observed something similar on concentric surfaces.
Unfortunately there appear to be aliasing effects in your preview screenshots so I can not make out the print lines in the interesting areas. I can see them on the edges, just not where it truly matters. But you may be able to check by zooming really closely into the areas where the lines start and/or end in the print.
What I imagine is happening is that the lines are a result of the individual segments of continuous print lines. Where the line starts, the adjacent path needs to joggle around that starting point. With a nozzle size (almost) equal to the print line, it leaves a 45° “jump” line through that one continuously printed segment. I expect that this is what you are seeing.
This can be avoided with simpler surface patterns (monotonic line comes to mind), but I expect you want that circular look?
Pure speculation: Maybe it’ll be less noticeable if you reduce top surface flow to the value you calibrated for the filament?
Or maybe an additional layer of ironing could help? I myself am not so happy about my X1C ironing skills though, so it may also make it worse.
I hope I have been able to help,
Yours,
Eno
Thanks for the insight.
I have used Archimedeal Chords quite often and have never experienced this before. It’s one of my favorite top patterns.
It would always draw the curves from one wall to the next wall, and doesn’t usually stop in the middle like that if that is what is happening.
I looks more like extruder scratches to me, but I haven’t had the time to watch it or experiment.
it’s just a new issue that I haven’t experienced before.
If I had to guess, the image is suggesting that your circular top pattern appears to be competing with the underlying layers(rectilinear). What I can’t explain is why. That’s because you already have 4 top shell layers and that should be more than enough to conceal the underlying infill structure.
Crossing walls won’t address this issue BTW. What crossing walls will do is make sure that if their is a gap in between the travel of the nozzle, the nozzle will instead of taking the shortest route, will instead move around the perimeter of the model thus minimizing stringiness in open cavities.
Here’s what I might suggest. Try changing these two things and see if it changes the pattern.
Change the internal infill to something else. I might suggest honeycomb because it is radically different pattern than rectilinear. If we see a honeycomb patter influence the top surface, then this might indicate a bleed-through of the shape. Then it may be remedied by lowering the nozzle temp in 5 degree decrements or increasing the fan speed. What you’re looking for is the upper layers to solidify more quickly if they are being influenced by lower structures.
Less likely but worth a try. Increase the top shell layers to 6 and see if that influences the pattern.
One thing that I’d like to know, is what does the sliced view look like. Can you post a view where it shows the layer just before the top shell and at the transition line. I’d love to know what the slicer thinks it sent to the printer.
The intent of this “disassembly” of layers is to better understand what is under each layer type for the purposes in seeing if we can guess how the top pattern is being influenced. In my example, this is using Honeycomb for the sparse infill just for a pattern change.
You nailed it Olias!
It’s definitely something with the layer just below:
Running through the extruder path reveals where the lines are being generated:
But not “why”. LOL
I just changed the solid infill to all Archamedial Chords and I think that should eliminate the lines. Since this is just for looks, not structural I think it won’t hurt.
The other thing I am battling is Elephant’s foot. I had that dialed out before but since printing with PLA again, it has reared it’s ugly head…errr “foot” again.
…the joys of 3DP!
@lexi Thanks for closing the loop. At least we got to the bottom of one mystery. 
I still would like to understand why the algorithm decided to paint those lines in that manner.
If you find you “Sherlock Jones” instinct kicking in and care to explore the cause, perhaps rotating the shape 45º on the build plate and see what the slice produces.
Thanks for sharing. That is very interesting indeed. Given the artifact that you showed at the start, this appears to be a mathematical ghost caused by the algorithm. This is the exactly the kind of thing that the math whizzes have to weigh in on, not us… that is of course… are there any math whizzes out there that might know he answer??? Speak up folks if you know. 
It amazes me how hard it is to get a decent flat top layer with silk PLA.
I mostly use PETG and the top layers don’t usually suffer from these issues.
The original problem:
Switched to all solid infill as Archimedial Chords:
Didn’t like the quality of the one above so I changed to Concentric solid infill, but the infill translated to the top layer:
None are ideal as they just don’t look all that good.
I am running an ironing calibration on this filament at the moment. If I don’t like the ironing results I will likely fill the pieces over with supports for the tabs and use some super smooth build plates to give the best outside appearance.
I believe the 2nd last layer is a bit over extruded hence excess material and leave scars on the last layer. The 2nd last layer isn’t monolothic, the last layer is though.
Reduce flow a bit more should solve it, yeah?
I usually print functional part and prototype part, so I don’t care much about aesthetic of the top surface. I do hate it though
