'Mis' Understanding of Top & Skin Printing

[PartySausage 32]

I'm putting a print together that has a couple of exposed flat surfaces at different heights. My belief was that any exposed upper surface would be printed in accordance with the top/skin settings regardless of where it appears. However the realisation dawned on me today when previewing the print that this isn't the case & only the upper most surface prints with the top/skin settings, whereas the other surfaces are printed in accordance with the top/bottom settings only.

I have different speed & flow settings for the skin wrt to top. hence would like to print those other surfaces as a skin too. It looks like the only way to do this is by changing the top settings to match the skin, however there isn't an option in Cura to set the speed & flow settings for top/bottom independently. Am I missing an easy trick here to use the skin for all surfaces or am I snookered?

 

Bed Handle Tripod Mount [Overture PETG, LW-0.4mm, LH-0.2mm, I-25%, T-E.235C, B.75C].zip

[Slashee_the_Cow 619]

Sorry for taking so long to get back to you on this, been dealing with things and also was sure the feature existed but couldn't find it.

 

You just need to set a value for Top/Bottom > Top Surface Skin Layers (set it to the number of top layers you've got if you want, Cura warns you if it's above 3 but who cares). Not only does that add some extra options to the Top/Bottom section (line width, pattern, monotonic, line directions) but in Material you'll get flow settings for the top surface (inner walls, outer walls and skin) and you can also set the Speed separately if you want.

 

The idea with the setting is that you usually only need the very top layer to look pretty, so you can print that with different settings that look better but might take a whole bunch of time longer than the "top" layers beneath it. But just because that's the original intention doesn't mean you can't use it to your advantage otherwise 🙂

[PartySausage 32]

Hi @Slashee_the_Cow thanks for even taking the time to look at my query. I'd never thought of doing that

 

So the trade off doing that way would mean that all top layers would be printed at the slower Top Surface Skin Speed & reduced Flow settings, which I would have to accept given that there isn't another way.

 

From a quick check; increasing the skin layers from 2 > 5 to match the top setting only increased the print time by 15-min. However looking at the preview of the model something seems a little amiss because I thought that with the those settings the line directions for all the top surfaces would follow the skin settings, but in reality they are different with the lines on the highest of the surfaces being aligned to the Y-Axis but all the others are aligned to the X-Axis, which was as they were when there were only 2 skin layers

 

 

 

 

[Slashee_the_Cow 619]

6 hours ago, PartySausage said:

So the trade off doing that way would mean that all top layers would be printed at the slower Top Surface Skin Speed & reduced Flow settings, which I would have to accept given that there isn't another way.

You don't have to do all the top layers at that setting if you want to (as designed you'd usually only do one or two), but then the lower top (oxymoron) layers would be printed with the same settings as the bottom.

 

6 hours ago, PartySausage said:

but in reality they are different with the lines on the highest of the surfaces being aligned to the Y-Axis but all the others are aligned to the X-Axis, which was as they were when there were only 2 skin layers

I'm putting my money on "one is on an odd layer, one is on an even layer". You could change Top/Bottom > Top Surface Skin Layers > Top Surface Skin Line Directions to a single number (just keep it in the square brackets, like [45] ) although that defeats the purpose of having them alternate directions (which is so you have a contiguous looking surface, not a bunch of chasms in one direction). You could try playing with the line directions (or do the maths) to find the magic combination required (like it could just be [90,90,0])

[PartySausage 32]

So I did a test design to get my head round this, The model was a series of steps that hds top surfaces on both odd & even layers & I tested it with different top layer/skin layer combo's. The Top/Bottom & Skin Line Directions were both set to [90, 0].

The result... yes you're right; It doesn't matter what combination you use the line direction is determined whether the top falls on an odd/even layer, which seems to be the wrong way round to me & I would have thought the line direction on the top surface should be orientated according to say the 5th layer based on the configured line directions for 5 layers & work down from there with the top most layer being in the same orientation regardless of the layer it falls on. With the way it works now you're pretty much taking pot luck with the line directions in a sliced design based on the layer no where the top layer sits in the slice with the only way to ensure that all the top surfaces lines align the same way is to set all the line directions the same eg [90, 90, 90, 90, 90] for the top/bottom & skin line directions... Not exactly ideal for a robust surface

 

 

Moving on to layer print speed/flow tests; With 5 top layers & 5 skin layers all the layers would be printed at the skin settings 30mm/s, 90% flow. With 5 top layers & 2 skin layers the first 3 layers would be printed at 60mm/s, 100% flow & the top two layers would then be printed 30mm/s, 90% flow as would be expected

With the current line orientation behaviour there would be little point in having skin layers = top layers as there would be no benefit from the increased print time

 

 

 

[PartySausage 32]

Bug report raised for investigation https://github.com/Ultimaker/Cura/issues/20000#issue-2721389748

[Slashee_the_Cow 619]

4 hours ago, PartySausage said:

The result... yes you're right; It doesn't matter what combination you use the line direction is determined whether the top falls on an odd/even layer,

That umm... wasn't what I was trying to say. Here's a test with 4 top, 2 skin with the skin line directions set to [90, 90, 0, 90]:

If we repeat the pattern from the start, and remember that we're using two skin layers:

90, 90, 0, 90, 90, 90, 0, 90 (8),

90 (9), 90 (10), 0, 90, 90, 90 (14), 0 (15), 90

90, 90, 0 (19), 90 (20), 90, 90, 0, 90

Ignoring that 15 is going the wrong way, the other problem with this arrangement is that layer 8 runs the same way as 9 and 10, so that's three layers with vertical lines on top of each other. There probably is a magic combination for any given set of layers, but my maths skills are lacking as to how to find it.

 

If you want all your top skins to have lines going the same way and make sure it's not the same as the layer below, you could use a single skin layer offset at 45 degrees from the top layers beneath it (i.e. top skin angle = [0], top angles = [45,135]) but obviously that doesn't work if you want the whole top to be in skin layers and don't want to enter several hundred numbers for the top surface skin layer angles.

[PartySausage 32]

Thanks again for your in depth dive-in to try & help me work this out.  I understand where you are coming from here & my underpowered brain is running at 101% CPU to do so. Likewise I cannot find an ideal solution that would orientate all surface lines on different layers correctly the way Cura currently works and there always seems be situations where the lines orientation of several layers is the same on consecutive layers in order to give the correct top surface orientation across all surfaces

As most of my prints are usually of an engineering focus rather than cosmetic, the line orientation isn't exactly a real world problem to me. When I spotted the differences with this model I got a bee in my nogging; so with a bit of rare free time to hand I decided to dive into the rabbit hole to try & understand why it's happening.

I raised the above bug report as I still think the top surface orientation should not be determined by the layer no of the surface and should be consistent across all surfaces & if my beliefs are accepted, with a bit of luck it's something that can be addressed

[Slashee_the_Cow 619]

Definitely something that would be nice to have, but... just don't hold your breath. The Cura team are pretty much being crushed by their workload as it is.

 

Something that might help is turning on ironing - I've found it works pretty well with the default settings and makes the direction of the surface lines nearly invisible.

[PartySausage 32]

Yeah Can't imagine this one would be high on the priority list. I've noticed a couple of annoying UI bugs that have manifested themselves in 5.9 & just trying to work out how best to document them for the bug reports.

What will be will be...Que sera, sera etc🎵 

[Slashee_the_Cow 619]

@PartySausage Before you report any UI bugs, make sure to try disabling all your plugins, restarting Cura and seeing if it's still there in case it's a bug with a plugin, not Cura itself.

[PartySausage 32]

Thanks @Slashee_the_Cow I'll try that. Not wishing stray off topic too much, the two bugs that have popped up are:

 

> After a period of inactivity where Cura has been sitting open in the background; the save button on a sliced model doesn't do anything and the file save dialog doesn't open. It still doesn't work even if I toggle a setting, re-slice & try to save again so have to close and re-open the Cura to fix it. 

 

> I've also had a random bug where the 'Slice' button doesn't replace the 'Preview' button on the 'Prepare' tab when loading a model but the 'Preview' button doesn't do anything & I can't select the 'Preview' tab either. I think this one may be related to the 'Replace Model' Mesh Tool where I've replaced a previously sliced model but I haven't don't enough testing to be sure. Again the only way to resolve is to restart Cura

 

If you've seen either of these & have any pointers I'm all ears 👂

[Slashee_the_Cow 619]

@PartySausage Can't say I've experienced either of those myself (although I use the "Automatic Slicing" plugin so I never need to worry about the button). You're better off posting those on the Cura board (because here isn't really where people will look for something like this) or just submitting bug reports (the best outcome from that is a slightly annoyed developer saying "here's how you do it, dummy").