burtoogle

Hi @ajiaoooooooo, I think those layers are OK, as @gr5 says, Cura tries to make the bottom of the spiralized object (let's call it a vase!) waterproof and that's how it does it. I can vouch for the effectiveness of that technique as I have several vases printed in PETG that are completely waterproof.

I have been printing some test bridges using PETG and getting good results. Here is a picture showing my little "flying support" test where I print a bridge across the pillars and then support on top of the bridge. I stopped the print early as the pillars were coming loose which is why the top isn't as thick as it should be. The bridge settings I am using with PETG (0.4mm nozzle, 0.2mm layers, 0.5mm line width, 245C) are: Bridge wall speed 50mm/s (same as normal wall speed) Bridge wall flow 100% Bridge skin speed 50 mm/s Bridge skin flow 100% Bridge skin density 60% Bridge fan 100% 2nd skin speed 30 mm/s 2nd skin flow 100% 2nd skin density 60% 2nd skin fan 0% 3rd skin speed 40 mm/s 3rd skin flow 110% 3rd skin density 80% 3rd skin fan 0%

Settings -> Travel -> Layer Start X/Y

The Minimum Infill Area was originally intended to stop little areas of infill appearing within an area of skin. It worked OK. More recently, this setting seems to have changed its behaviour and now it seems to do nothing useful and, indeed, tends to break things by making unwanted holes in the skin layers. EDIT - actually, I'm not sure that the behaviour really has changed but it does seem to conflict with with the skin shrink/expand feature. This setting is now redundant anyway as the settings for shrinking/expanding skin regions provide better control. I recommend setting the min infill area to zero and ignoring it.

My first test was with PLA and I have just printed another part in PETG. Again, the end result was very good. In this instance, the interface layer density is only 40%. Previously, I have had some issues with the interface sticking to the skin but today, using 100% fan for the first skin layer, the support all came away very easily and the skin looks very good.

So I have done some coding and am trying out forcing 100% fan for the first skin layer above support. The result was very good, with a support interface skin density of 100% (max adhesion likelyhood), the support came away very easily and the resulting surface on the part looked super. I repeated the experiment without the 100% fan and the support was a bit harder to remove with no real difference in the quality of the skin. I think that it would be best if the fan used for that skin isn't just 100% but could be specified (I know, yet another setting) but if someone has a mega-fan and they don't normally use 100% then being able to specify the fan amount is needed. I haven't yet tried modifying the fan for the situation where there is support on top of the model and I wonder if it's going to be beneficial there.

It could well be a problem with the model, can you post the model file?

Hello @Keventurist, thanks for your input. IMHO the skin above support should not be treated like a bridge and I have further Cura mods ready that will stop that happening (along with some other tweaks). But it's an interesting idea (using more fan for the areas above/below support regions and worth trying out. I will look into it.

Actually, further investigation shows that the real problem here is the large value of Minimum Infill Area. Reduce that and the skin shrink/expand settings are OK as they were. I was the original creator of the Min Infill Area setting and it is now pretty much redundant because you can shrink/expand the skins which you could not back then. Also, looking at the Cura code which has been reworked by someone else since I worked on it, it doesn't appear that the Min Infill Area setting does what I would expect any more. I recommend setting it to 0 now.

You need to reduce to skin removal width to 0.1 or less.

At the moment, Cura always prints walls and skin separately and given how the program is structured I can't see that being easily changed. However, I wonder if there is some scope for connecting the inner, circular walls to the outer walls with other walls. That would achieve similar results in terms of adhesion. Personally, I have solved the small circle adhesion problem by printing first layer walls very slowly so I would not have any trouble printing your example above.

Could you please post a 3mf file so that I can see what settings you are using.

This is using a skin removal width of 0.5 and a skin expand width of 2.

Set the Skin Removal Width setting to 0.5 or less and the skin will be OK when using 4 top skins. There is something weird going on though because if you set top skins to 3, then the skins are OK without using a small value of Skin Removal Width. But setting the skins to 4 makes it bad unless the above setting is changed.

Hi, could you please post the model for us to look at? Thanks.

Hello @daoust, sorry but you have hit a big problem with Cura that it doesn't make a good job of thin walls. The problem boils down to the fact that all walls have to be printed as a pair of lines and not just a single line. Cura tries to make amends by providing "wall overlap compensation" which makes a second wall that runs close to a first wall thinner so as to reduce the overall width but, unfortunately, the overlap compensation has many bugs and is not guaranteed to make a good job. It remains a problem area.

Using a line width of 0.35 for both outer and inner walls makes it fill the teeth. How well this would print using a 0.4mm nozzle I do not know.

Hi @Verne64. Yes choosing the direction of the bottom skin layer is something I have been working on. I already have a PR in the pipeline that would make a better job of your example. The original bridge skin line angle algorithm (not written by me) only works when the bridge is supported by more than 1 region and in your example the skin is only supported by one region so the skin line angle is not changed from the default. The strategy used in the new code in the PR is to detect the longest unsupported edge and it aligns the skin lines to be parallel to that so in your example the skin lines would be parallel to the wall on the left. It also alters the direction of the lines on the next 2 layers to be +/- 45 from the direction of the first skin. If there is only 2 skin layers then the 2nd will be at 90 deg to the first. I don't think the PR will make it into 3.3 but maybe it will be in 3.4. I don't claim that the strategy will be best for all bridges so I am continuing to work on this.

That's weird, why should printing using the USB cause flaws to appear where the z-seam runs? Personally, I don't print using USB as I have seen quality issues before caused by lag in the USB data stream.

Ahh! yes, I know what you mean now. There's a setting that adds an extra perimeter around skins which I never use (always set it to zero) It's Shell -> Extra Skin Wall Count. Anyway, I'm glad you are having fun experimenting!

Hi Frank, understood. BTW, I have submitted a fix for the holes that are shown when the gcode is loaded back into Cura (it's https://github.com/Ultimaker/Cura/pull/3650 if you are interested).

@Frank5300, those G0 lines that occur at the end of some of the layers are travel moves and you will see that they are actually moving a very small distance. I can't remember right now where they are coming from in Cura but they are probably harmless.

Hi @Torgeir, yes, loading the STL file into Cura does show those wacky holes but they really aren't there. They are caused by some deficiency in the gcode reader/visualisation in Cura. You can look at exactly the same gcode in other viewers (I have used s3d and craftware) and those holes are not present.

Hmm, well I can't explain that. I have looked at your gcode with 2 viewers (s3d and craftware) and can see no flaws where the z-seam runs. Looking at the gcode text, on every layer change it fiddles with the acceleration. I don't see why that should cause the problem you are seeing but it may be worth not making that change to the acceleration just in case it's having a weird effect. I can assure you that I have printed that same model today with zero flaws so I don't think there is a general problem with the spiralization but, obviously, it's not coming out right for you. BTW what happened in the middle, did you change the filament?

Still not quite sure what you mean about the wall lines. Could it be that you are referring to the infill? I note that you are using quite sparse infill. The coasting percentage is not really a percentage of anything but it just gives you a means of controlling the amount of coasting you get. The coasting distance is influenced by the difference in extrusion rates (which is proportional to print speed x flow) of the wall before the bridge and within the bridge. It is also influenced by how long the wall before the bridge is because if it is very short, the extruder may not be completely up to normal pressure. By experiment, I decided on a scaling factor that, for me, gives reasonable results but as it may be wrong for other setups, the coasting distance can be tweaked by that setting. Hope this makes sense. Finally, if you don't like the coasting, just set that to zero and it is completely disabled.