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Special introduction: Ultimaker Cura engine improvements with Arachne alpha


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Posted · Special introduction: Ultimaker Cura engine improvements with Arachne alpha

Hello everyone, 


We don't often release an alpha version of Ultimaker Cura... So what's different this time? 

Well, this Ultimaker Cura alpha contains such a huge slicing engine overhaul that we really need your help! We want to give users the chance to test this early release as soon as possible. Your feedback is vital to help us release the very best stable version of Ultimaker Cura in 2021. 


So what's the big change? 

The Ultimaker Cura slicing algorithm is enhanced with the Arachne code library. This fundamentally changes how Ultimaker Cura handles inner parts of a model. For example, let’s say that you want to print within a space that's 4.4 mm wide. Using the current slicing engine, a constant 1 mm line width could leave a 0.4 mm gap that would be tricky to fill. 

Instead, Arachne adds variable line width to the slicing algorithm. That could mean printing 1.1 mm across all four lines to ensure good fill and prevent the 0.4 mm gap. 

In this way, the we intend the upgraded slicing engine to optimize line positioning and variable line widths – especially for thin walls and around corners. 
This should result in: 

  • Better handling of thin walls and filled gaps  
  • Smooth line transitions inside tapered geometries  
  • General print quality and strength enhancements  
  • Reduced print head movement for filling in gaps 



Which new settings need testing? 


The improved Ultimaker Cura engine gives you new settings that will optimize printing thinner walls, including:  


  • Variable Line Strategy (3 options: Center Deviation,  Distributed, Inward distributed) 
  • Minimum variable line width
  • Wall transition length 
  • Wall transition angle 
  • Wall transition distance filter 


So now you have the chance to peek into Ultimaker Cura’s future, test these settings, and see how they work for you! 


If you decide to tune these settings and doing so results in better print quality, please share your findings with us. Doing so will help us set default values for both Ultimaker and third-party printers. This is particularly relevant for third-party printers, because we don't have these available for testing and updating their profiles. 


How to start testing : 

  1. Download Ultimaker Cura Arachne engine alpha
  2. Run some tests with prints that you're familiar with 
  3. Consider trying a print with thin walls to test the difference 
  4. Share any feedback or bugs via GitHub. (Simply enter a bug or feature request, you'll automatically find the correct feedback template.) 


Read this before you send feedback  

During the alpha test we will keep this support article up to date with news and known bugs. Please take a look before you post a bug report. This will prevent extra work on your end and ours. 



Please remember that this Ultimaker Cura alpha is not suitable for ‘normal’ use. It should be only used for testing. In addition, this version represents a huge code change, so some features – like fuzzy walls – are not yet supported. There is also a higher chance that you run into a bug (some known, some unknown). These might reduce print quality. Due to the holiday season, responses from Ultimaker might be a slower than usual. 


And then finally... 


A HUGE thank you to anyone who can contribute to this alpha test! 


We're incredibly excited about what the Ultimaker Cura engine improvements will offer the global 3D printing community. And by working together, we will be able to turn it into the best possible version for everyone. 


And if you want to learn more about the framework behind the Arachne engine, you can read the scientific article it’s based on here 


Have a wonderful day! 

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Posted · Special introduction: Ultimaker Cura engine improvements with Arachne alpha

This sounds encouraging, the two features which give me the most issues in terms of quality are compensate walls overlap and fill gaps between walls, i have both disabled but sounds like this will correct the issues those two features were targeting. Fingers crossed !

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Posted · Special introduction: Ultimaker Cura engine improvements with Arachne alpha

All I can say is wow.  I will have to go check the settings if they need to be more specific.  But I downloaded the new Arachne Software yesterday.  Since that time, I printed a Water Tower and a Raspberry Pi case.  With this update, I have had no under extrusion, stringing, and no blobs, that I have had in the latest stable version of Cura 4.8.


This is the first time since upgrading to a direct drive (which has given me slight headaches since June/July) that I am a thoroughly happy Ender 3 Pro consumer again.  I'm really tempted to run a lithophane print on this and compare it to the one I just printed for my wife, but first I have to finish printing the water tower for my wife.


Keep it up guys.20201225_174624.thumb.jpg.07fd6c0457b3fc74b3cd4c3fb197d1cb.jpg20201225_174643.thumb.jpg.c4b6483099b0c00ea373a4c956380b1b.jpg20201225_174630.thumb.jpg.b79b01fe748ab05756787edbabb755af.jpg20201225_193347.thumb.jpg.edcd0fd48e2fca68fb31839ea675936e.jpg20201225_193343.thumb.jpg.eb7cb8479b1081d52a16cec2a647f232.jpg

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Posted · Special introduction: Ultimaker Cura engine improvements with Arachne alpha

It's a slow sequestered holiday so I downloaded the Arachne version of Cura just to try it, as I had a print with quite a few curved surfaces about ready to print, so I said 'what the heck' and used the new version to slice it.


It's printing now jury is still out on any noticeable difference, but there was one thing I immediately noticed when preparing the model.


On the Print Settings to the right, there are little arrow characters which normally correspond to whether you have the particular section expanded or closed.  They normally point left '<' when collapsed and down 'V' when expanded.


In the Arachne Cura, they do not change as expected.  Sometimes they do not point down when expanded, other times they stay pointed down.


Just something I noticed immediately on trying it.

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    Posted (edited) · Special introduction: Ultimaker Cura engine improvements with Arachne alpha

    Ohio State is up by 3 touchdowns at the half and an Arachne print has finished.

    Same model, same settings, mirrored using Cura.  On the left we have Arachne and on the right is 4.8.0.  The printer is an Ender 3 Pro.



    There is some Z-banding on the Arachne print up to about 1/2 way up and then from there to the top they are really close to being identical.  The 4.8.0 version was printed first.  I will let the Cura Team analyze the banding.  The parts were printed one after the other.  The color makes them tough to photograph.


    The movement of the layers of the base of the Arachne version went down oddly.  One loop on the right hole, one loop on the middle hole, and one loop on the left hole, then start over on the right hole, until the inside wall was built.  The outside walls went down normally with 3 loops around each in turn before moving to the next hole.


    Those of you who know about such things will recognize that the Honda Goldwing in my profile is fitted with dual Weber IDF carburetors and topped with velocity stacks.  These are my take on old style Stromberg ram stacks from early V-8 drag racers of the 1950's and 60's.  I thought they would make a nice change of pace at shows.  Nobody will ever notice the banding since a light must be held at just the correct angle to show them.  My luck will be that the sun is at just the right angle when the judges come by.


    Edited by GregValiant
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    Posted · Special introduction: Ultimaker Cura engine improvements with Arachne alpha

    after trying a couple of prints, in terms of quality, 4.8.0 produces better results if you disable 'fill gaps between walls' and 'compensate wall overlap', which i have had to do for a long time as they are not good.

    Clearly Archane looks to address the issues these settings have, but for now there are many surface artifacts with Archane and in reality it's not much better than 4.8.0 in terms of visual quality with these problematic settings enabled.


    Obviously once Archane does what it is meant to it will fill any gaps between walls (should make stronger prints, although that's debatable if those gaps make much difference) and corners etc will be sharper as the overlap compensation will be sorted out. However for now i would rather put up with gaps and rounded corners to avoid these surface artifacts.


    Looking forward to trying another build !, i am sure it will be great in the end

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    Posted · Special introduction: Ultimaker Cura engine improvements with Arachne alpha

    I tried Arachne on one small print, but after printing I noticed that the support interface was not created so the overhang was bad.  I double checked the settings and it should have been there, but wasn't.  I think I'll wait for Arachne 2.

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    • 2 weeks later...
    Posted (edited) · Special introduction: Ultimaker Cura engine improvements with Arachne alpha

    Hi all,


    this is one of the best/most important news for my daily work with Cura. Juggling and fine tuning line widths to get cleanly printed, solid walls is one of the most time consuming and infuriating tasks for me, even more so because every other slicing software seems to be able to handle this with ease (and for years already, might I add).


    I print a lot of parts for customers, so I don't really have influence on wall thicknesses. Moreover, I'm using horizontal offset to make parts more precise which nullifies any design guidelines ("use a multiple of X as wall thickness" - doesn't make sense)


    finally, I just hate it when my printer tries to shake itself to death 🙂 it might work on Ultimakers with their mechanics, but it just doesn't seem healthy. And I've had the rods fall out of the clips already....


    is there a rough timeline on when this might be implemented into the main release?


    best, Niklas

    wall Thickness.jpg

    Edited by neute
    image attached
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    Posted · Special introduction: Ultimaker Cura engine improvements with Arachne alpha



    I tried CURA Arachne Alpha on small parts for hausemodels 1:100.


    1. open in Cura Arachne an existing Project (Cura 4.8)

    2. used standard values for  "Variable Line ....":


    3. Sliced with the same parameters I used for Cura 4.8


    The result with CURA ARACHNE Alpha looks like this:



    Same sliced with CURA 4.8:



    Attached a 3mf file created with CURA ARACHNE Alpha.


    I have to play with extrution and other parameters as soon as I have time.


    Kind Regards



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    Posted (edited) · Special introduction: Ultimaker Cura engine improvements with Arachne alpha

    Hi, first of all, it is a pretty good update, I've really enjoyed it - until I stuck with this model


    So, I've printed the model and found out some strange artifacts on the surface, when I tried to find the option which created it - I found Variable Line Strategy, and on the "Center Deviation" option, at first sight, the problem was solved, but it creates another - hole between walls. When I switched back to Cura 4.8 - there were no problems on the surface


    Long story short - ATM it's pretty tricky to print this model clean on the current Arachne version

    Center Deviation.jpg

    Cura 4_8.jpg



    Inward Distributed.jpg

    Edited by DiodorOFF
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    Posted · Special introduction: Ultimaker Cura engine improvements with Arachne alpha

    Im basically using the default settings with an UM3 on arachne alpha.

    There are strange things happening, when the infill is at a narrow area there are inserted mini travel moves (e.g. these blue dots in the circled area) that cause the printer to nearly stop moving (I'd say it's below 1mm/s in these areas). Regular infill works, it only happens when the infill area is quite small.

    An option for the "order inner walls by inset" that affects only the first layer would be good. I had some issues on the first layers with an object with many holes, the printhead combed across everything and pulled some of the printed single lines away by doing so. 

    Overall I like the strategy the slicer uses, it's especially useful for small objects the have areas where walls are not a multiple of the line width. I made some replacement caps for some connectors that came out perfect with a 0.25mm nozzle, though they have walls that are only 0.4mm wide. 


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