Print/Slice object with a cavity using TPU with Ultimate Cura

[jnrehder 0]

I would like to slice an object with a cavity using Ultimaker-Cura-5.1.1. The printout works wonderfully with PLA (even without support structures), but I have big problems with TPU.
It seems that the printhead is regularly dragged across this cavity, creating threads in the cavity and rendering the print unusable. Other forums recommend tweaking the print settings until these threads no longer appear. I tried the build in settings for TPU and also used the material parameters, recommended by the manufacturer - but this did not help much. I print with a Anycubic Viper.

 

Question: Is there a setting in Cura that prevents the printhead from being dragged across cavities?

 

UPDATE: It doesn't seem to be Cura's problem (or is it?). See my update below.

Edited November 4, 2022 by jnrehder
Update

[GregValiant 1,251]

Figuring out which "Combing Mode" to use is the usual fix.  Adjusting the "Layer Start" X Y in the Travel section and the "Z seam Location" in the Walls section can help as well.

[jnrehder 0]

Thank you GregValiant.

 

I checked the Combing Mode setting. It is "all on".

 

I looked at the head movements in the simulation. Obviously my guess about the head going over the cavities was wrong. The movements seem to be OK in Cura.
The hair still appears?! Can it be that the printer optimizes the movements and then makes the direct path through the cavity? Very strange.

I've attached a picture of the "hair". This is very fine and dense hair that is difficult to remove.

[GregValiant 1,251]

What is your setting for "Walls / Wall Ordering"?

When that is set to "Outside to Inside" then the outer wall goes down first and sometimes when the printer is making a circle around a hole, the extrusion will not stick where it is supposed to and instead the "loose" extrusion gets pulled across the center of the hole feature.  In that case you get strings (until the extrusion starts sticking again) but the tool path is correct.  So make sure you are printing walls "Inside to Outside".  Slowing down the "Outer Wall Speed" can also help but you are already probably printing pretty slow.

[jnrehder 0]

I use the standard setting "Inside to Outside" for Wall order and the recommended speeds by Cura.

30mm/s for the outer wall and 60mm/s for the two inner walls and fill (I use three layer for the walls). Maybe I try the same speed for the two inner lines?

[MariMakes 198]

Hey @jnrehder,

 

Welcome to the Ultimaker Community 🎉

Just a quick tip when you are checking if stringing is caused by your Cura settings. In your preview you check the travels as a linetype. 

Dark blue travels will not be retracted, light blue travels will be retracted. In your case you want to check if you have light blue or dark blue travels where you see the strings. 

[GregValiant 1,251]

Just for a reference, I have a bowden tube printer and I print TPU at 12mm/sec.  Any faster than that and I get jams in the bowden tube.  Because of my situation, I don't use retraction at all with TPU.

[jnrehder 0]

Thank you GregValiant. I will reduce the print speed and try again.

 

Regardless, I've found that the hair can be removed quite easily with boiling water.

[GregValiant 1,251]

I print gaskets and seals with TPU.  I haven't had much luck printing taller items.  So far as I can tell TPU is fuel proof and used as intake manifold gaskets it has stood up to the heat on top of the cylinder head of my motorcycle.  The ones I was cutting from a sheet of gasket material would get misshaped from the ethanol in the gasoline.  I would have to replace them at every carburetor cleaning.  Now that I have a way to make them fairly quickly...I don't have to.