SOLVED Extra wall with no extrusion Cura 4.8

[cncbeagle 1]

I am trying to print a ~125mm diameter hollow cylinder with 3 walls on my custom coreXY printer. It is setup with a 0.6mm nozzle and a V6 volcano hot end. I am trying to print a 2.7mm wall with three 0.9mm wide 0.45mm high layers. No matter what combination of line width and many other settings I have tried I always end up with 4 walls including an inner wall with little or no extrusion. With PLA this just adds time to the print. However, with PETG there is a little oozing leaving small specks and then a gap when the next wall begins. How do I eliminate this useless extra inner wall? I have tried 0-100% infill with different patterns including concentric. I have tried using 0.899mm and other similar values for walls to eliminate roundoff errors. I have tried no top and bottom layers up to all bottom layers. Optimizing the wall printing order just moves the gap to a different wall.

 

The cylinder is just a test leading to printing fittings for my wood dust collection system. Most of the fittings are just variants of a cylinder. The extra time taken for this useless inner wall adds up quickly for a fitting with 500+ layers.

 

I print mostly functional things for my on use and have been using Cura for several years (since version 15). With this new coreXY I am able to print much larger parts so I'm looking more carefully at the resulting gcode.

[gr5 2,167]

Please look at your part in PREVIEW mode and make sure "color scheme" is set to "line type".  Once you do this it will show infill as a separate color.  I think you'll find that the "4th wall" is part of the infill.  You can get rid of that 4th wall by trying different infill patterns that come with cura.

 

If I'm wrong then please provide a screen shot that shows the lines in different colors and also please post your project by doing "file" "save..." and post the resulting file here.  Note that it will contain your STL file(s) so hopefully that's okay.

[cncbeagle 1]

Thanks for the help getting started.

 

Here's a image showing the wall in different colors at the highest magnification I could achieve. It appears to show two shells with a single inner wall. Great that is my goal. However, when you look at the resulting gcode file you will see there are two inner walls. The first inner wall starts at line 516 and extrudes material at an expected rate. The second inner wall starts around line 588 and extrudes almost nothing. The extrusion rate for the second inner wall is only about 0.5% of the first inner wall. Not only does this waste time but it also leads to other problems with PETG which tends to ooze. The two outer walls begin at line 660 and extrude a similar flow to the first inner wall. The higher layers follow the same pattern.

 

As I stated in my initial post my goal is to print some fittings for my dust collection system. They are all some variant of a hollow cylinder with relatively thin walls. Many of them will be several hundred layers and the extra wall greatly increases the printing time. With PETG it also leads to gaps following the extra layer as some plastic has oozed out of the nozzle so when extrusion resumes there is a gap of missing plastic. There is no gap between the start or end of the other walls so it is not a tuning issue.

 

I have included the project file along with the gcode file. I have printed this test piece in both PLA and PETG. The PLA print was acceptable but takes about 25% longer to print than necessary. The PETG print was not acceptable due to the gaps formed after the extra blank wall and also takes longer to print. PETG is preferred in this application due its superior layer bonding and overall strength.

 

How do I configure Cura to eliminate this extra useless wall? As I said I have tried many combinations of wall and extrusion widths, infill patterns, infill percentage and anything else I could find. Every combination that appeared to have 3 solid layers also had a fourth useless layer.

 

John

TM_5in_ID_duct_test_045-PETG.gcode TM_5in_ID_duct_test_045-PETG.3mf

[gr5 2,167]

Ah!  I didn't realize your part was very thin.  The term "wall" has a different meaning for thin parts.  In Cura "wall" is the portion that surrounds  the "infill".  You don't have any infill (would be colored yellow in your picture above - the green is just an inner wall).

 

Okay this is a common problem.  I have 2 solutions for you.  Okay 2 plus some settings.

 

One is to try the burtoogle (aka smartavionics) version of cura - it's much much better at printing thin walls like this:

https://github.com/smartavionics/Cura/releases

 

There's also a few settings that might help you but I'm not familiar with them:

"print thin walls" may make things better or worse

"minimum wall flow"  <-- if you increase this to say 50% it should reduce or eliminate those 5% flows yet hopefully no gaps in the wall

 

 

The other seems like a hack but it is an extremely common hack that lots of people do.  Some people do this for 90% of their prints.  It works well for cylindrical parts like this but not so well if you have a Y shaped fitting.  And it works well for when the outside diameter of the fitting needs to be precise but you are a little less about the inside diameter.

 

So you model the fitting in CAD as a solid.  Without a wall thickness.  For example a solid cylinder.  Which may change it's diameter as you go up.  then in Cura you disable infill, you disable top and bottom skin (set skin thickness to zero), and now you can set the wall thickness precisely with Cura's wall settings.  And it won't do this nonesense of printing at 5% flow.

[cncbeagle 1]

@gr5

 

Thanks for the quick helpful response! The minimum wall flow did the trick. It cut the estimated print time from 29 to 22 minutes and eliminated the extra inner wall. The thin wall setting did not eliminate the extra wall. 

 

I will definitely try the solid model trick for some models but maybe not for these fittings like the Y type. I will give it a try for the sweeping 45 degree elbows.

 

I'll also look at the other version of Cura you linked. I had no idea such a thing existed.

 

Thanks.

 

John

[gr5 2,167]

Actually now that I think more - it should work on Y fittings as well.  As long as the openings to the fitting either face up (roof) or down (floor).  Hmm.  I guess it's complicated the tip of the "V" in the Y is a roof I suppose.  Maybe it won't work well.  I'm not sure.