Why did PVA support default pattern switch from Triangles to Zig Zag in Cura 5.2.1 (vs 4.13.1)

[jasonrohrer 8]

In 4.13.1, if I toggle the support extruder back and forth from 1 (PLA) to 2 (PVA), it auto-switches the default Support Pattern from Zig Zag (for PLA) to Triangles (for PVA).

 

But in 5.2.1, the default Support Pattern is Zig Zag no matter which extruder (PLA or PVA) is chosen.

 

I've successfully printed a very intricate PVA-supported PLA print by slicing with 4.13.1 (there was a bug in 5.2.1 that prevented the slice from completing).

 

Now I'm printing a simpler PVA-supported PLA design, and 5.2.1 is slicing it just fine.  However, the PVA supports are detaching from the raft after several layers, and the print is failing.  I've tried the print twice, with the same thing happening both times.

 

I'm trying to figure out what I'm doing wrong on this new, simpler print.  So I went back and sliced it in 4.13.1 and found this difference in default support patterns for PVA.

 

And indeed, the Zig-zag shape seems really thin and weak, and seems to be what's causing it to detatch so easily (one end of the Zig Zag fails to adhere fully, and then there's nothing to really hold it in place, and it eventually works the rest of the Zig Zag free).

 

Can anyone speak for the reason for this change in default Support Pattern for PVA?

 

Admittedly, the failure could be caused by some other issue.  I'll know for sure once my 4.13.1 slice finishes printing.  But 14 minutes into the print, it's doing much better.  The Triangle PVA supports look well-defined and well-adhered, like a little glass house building up.  Where the Zig Zag supports generated by 5.2.1 were already looking quite birds-nesty and wiggly by this point.

 

(I'm also noticing that the 4.13.1 print time is about 30% longer for pretty much the same settings... 2:09 vs 1:39 for 5.2.1)

Edited December 30, 2022 by jasonrohrer

[jasonrohrer 8]

And I found the change here, on June 2:

 

https://github.com/Ultimaker/Cura/commit/0f48878bc7ced68ca4c121088d8b2e54c4872c0f

 

The BB nozzles all defaulted to Triangles before this change.

[jasonrohrer 8]

Also, this contradicts this article from November 8, 2022:

 

https://support.makerbot.com/s/article/1667337600656

 

Quote

Support pattern. The default support pattern is set to triangles to allow consistent and reliable extrusion. Alternatively, for less complicated models, the support setting can be changed to gyroid to ensure faster dissolution.

 

[MariMakes 199]

Hey @jasonrohrer,

 

I know that the new support pattern has been introduced in Cura 5.1, together with a number of other support changes,  based on a lot of research by our Print Profile Experts. The change was one of the highlights of that release. You can read more about it here https://ultimaker.com/learn/ultimaker-cura-5-1-stable-release

Their technical motivation can be found here: https://github.com/Ultimaker/Cura/pull/12488

 

Do you have a project file for us? It contains the printer and settings we need for troubleshooting. 
To save a project file go to File -> Save project.

I can have one of the Print Profile Experts take a look to see wha tis going wrong. 

[jasonrohrer 8]

Thanks for the info!

 

Quote

a new zig-zag pattern will be used, instead of the previous triangle pattern.

 

Zig Zag isn't exactly "new", since it was an option in 4.13.1.  But it's definitely new as a default.  Maybe they also tweaked Zig Zag?  And it's certainly faster, and I'm sure it dissolves quicker too.  However, I don't see them making an argument that it's "more reliable"  They say:

 

Quote

"you can now expect faster print times and more reliable support structures."

 

But... it's way less reliable.  Less material put down, less cross-lines holding it together, no external wall for added stability, less horizontal expansion, etc.

 

I have opened more specific bug reports on this issue already on Github.  The lack of reliability isn't a bug, so I haven't reported that.  But there are floating bits in the support structures:

 

https://github.com/Ultimaker/Cura/issues/14184

 

Another change is that horizontal expansion defaults to 1.0mm now, instead of 3.0mm.  This is much riskier in terms of print failure.  I'll take some images of side-by-side finished prints from the 4.13.1 defaults and the 5.2.1 defaults.

 

4.13.1 "encases" the model in support material (thanks to the 3.0mm horizontal expansion), where 5.2.1 has second-layer supports completely "on top of" part of the PLA, which is risky, and comes close to failing.

 

[jasonrohrer 8]

On left are samples printed with Cura 5.2.1

 

On right are same models printed with Cura 4.13.1

 

The second image shows a close-up of how the second-layer supports came close to failing.  I think this is because of the reduced horizontal expansion.  This causes the supports to "skip" the layers where there is solid PLA in the middle.  Then the supports try to "start up again" above that PLA shelf, but they have trouble adhering.

 

Whereas, with 4.13.1, since the model is encased in PVA, there's a nice wide "foundation" for the second-layer PVA to adhere to.  That foundation includes PVA at the edges and PLA in the middle.  I'll post some screens from the slicers in a minute.

supportTest.stl supportTestShort.stl

[jasonrohrer 8]

Here's what Layer 92 looks like from 4.13.1

 

You can see how the supports above the PLA shelf "bridge" to connect with the PVA scaffolding on the outside of the model.

[jasonrohrer 8]

Also, in case it's not clear, here's what the model looks like.

 

Obviously, in real life, you'd never print this model vertically like this.  However, it was designed to be a good test of multi-layer supports.

 

In real life, I am printing much more complicated structures that have compound-overhangs like this and no possible "support-free" print orientation.

 

 

Edited January 2, 2023 by jasonrohrer

[jasonrohrer 8]

And here's layer 92 from 5.2.1:

[jasonrohrer 8]

After more layers are printed, you can see a pretty dramatic 1.0mm overhang on the second-layer PVA supports.  This is asking for trouble, I think.

[jasonrohrer 8]

This is not a bug, so I won't report it as such.  But it is risky.

 

In general, I've found 4.13.1 to be much more reliable than 5.2.1

 

And I'm a brand new user (just got an S3 for the first time a few weeks ago), so I have no previous experience with either version.

 

 

I started using 5.2.1 right away, as recommended by UltiMaker, but I ran into one problem after another.  Every time I reverted back to 4.13.1 as a sanity check, I found that the problems are resolved.

 

This has not been a great experience as a new user of a $4000+ printer.  If I was stuck using 5.2.1 exclusively, my new printer would be useless to me.

 

Fortunately, through many hours of investigation and experimentation on my part, I've found my way back to 4.13.1, and it seems to be quite reliable.

 

Maybe for users that need cutting edge features, like metal printing, the should be steered to Cura 5.  But beyond that, it doesn't feel like it is quite ready to be called THE version of Cura that everyone should be using.

 

Seems like it might be wise to continue flagging it as experimental or beta or something, and calling 4.13.1 the official "Stable" release recommended for users who need a reliable workhorse and don't need cutting-edge features.

 

I'm speaking as a software developer with decades of experience shipping systems to end-users, so I know this might be a painful pill to swallow.  But part of the UltiMaker brand is that it "just works," and that brand image is being weakened by Cura 5, at least in its current state.