If you haven’t yet, check out my article on the Velocity Painting technique.  To quickly summarize my previous work, this post processing technique varies the speeds of your model’s outer shell to give it a texture, picture or design.  This is a very cool concept and I applied it to a few different vases and to the ever faithful Skully.  While printing the Skully I noticed some EXCESSIVE ‘stringing’ in the infill of the model.  I thought nothing of it and sliced up a file for a 3D printed hand with a checkerboard pattern ‘painted’ on it.  This is when it became glaringly apparent that something was wrong.  Which led me to investigate what could be causing this Velocity Painting issue.

velocity paint issue-phoenix palm
Top print before Velocity Painting with Cura 3.6, Bottom print is after modifiying with Velocity Paint. Look at the ‘strings’!

What’s the Velocity Paint Issue?

I had to stop the print.  Something was wrong, REALLY wrong.  I haven’t had a print that looked this bad in a very, VERY long time.  The amount of stringing was so bad that I thought there was something wrong with the filament.  I loaded up the original file of the UnLimbited Phoenix hand and it started to print without issue on the same printer with the same Hobby King Transparent Red filament.  Hmmm!?

velocity paint issue-skully nose
Cura 3.6 Gcode on the Left, The Velocity Painted Cura 3.6 Code on the Right. See the travel marks?

While watching the modified file print, I had noticed what looked like stringing from excessive heat.  Except the problem wasn’t due to heat.  The extruder was extruding on some of the travel moves!  After opening the modified Gcode file, my suspicions were confirmed.  The Velocity Paint issue was in the modified Gcode.  I opened up the original Gcode and could see that problem wasn’t there.

Verifying Settings and Reslicing

I went back through my settings and verified that I hadn’t accidentally changed anything.  My infill, top/bottom, and walls were all set to the same speed.  I even changed my initial layer to being the same speed as the rest of the model.  The Velocity Paint issue remained.

I changed the speed of the travel moves to much higher, and I changed retraction speeds.  The biggest change came from disabling retraction completely.  This cleaned up the model a little bit, as I show below, but STILL the Velocity Painting issue remained!

velocity paint issue-cura-no retract
Cura 3.6 with no retractions after Velocity Painting, you can see the issue is still there in the nose, but not the teeth.

How About a Different Slicer?

Maybe it’s something that Cura is doing?  I decided to try out KiSSlicer.  This is a pretty rough profile, but I just wanted to see if the problem was related to some kind of wipe/retraction that Cura was doing.  I sliced up my rough draft on Kisslicer and ran it through Velocity Paint.  The problem was GONE in the layer view.  I even went back and used an older version of Cura and the problem was still there.  So the problem seems to be related to however Cura handles travels.

velocity paint issues-kisslicer
Top is KISSlicer before Velocity Painting, the Bottom is after. No apparent travel lines between them.

So What Now?

I have reached out to the team at Cura and also to the Velocity Paint app’s creator, Guillaume.   I will update the article with any further information that I receive, but for now, I would hesitate to use any kind of  Velocity Painting technique with any version of Cura (as of v3.6).


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