2mm hollow print - wall issues

[erind 0]

Hi,

 

I am printing a hollow object with a 2mm wall, using Colorfabb PLA/PHA and a 0.8 nozzle.

Printing with a 0.4 layer height and PVA support, with a 100%infill.

 

The majority of the wall prints fine, but when it gets to one side there are gaps in the outer wall and the inside wall is blotchy. I've also noticed that the top layer in some areas has gaps between the outer wall and fill. I have printed with a few different settings for wall thickness and top/bottom thickness - but cant seem to resolve the issue. This is not to do with the printer or material feed as I tried it on two seperate UM3E printers. Pictures attached.

 

Any help much appreciated as I am without clue!

[gr5 2,168]

If you want a nice looking print you have to be patient.

 

Overhangs are always difficult - the old rule of thumb is anything more level than 45 degrees is difficult (vertical walls are easy) although I've seen overhangs of about 80 degrees from vertical (10 degrees from horizontal) that look suprisingly... fair.

 

One way to improve the print is to go down to 0.3 or 0.2 layer height.  Right now with 0.4mm layer height and somewhat extreme slopes (overhangs and slopes) you have huge shifts from one layer to the next giving your part that iso-line look.

 

Another way to improve the print is with infill.  Or did you model the part hollow?

 

Another way to improve the overhangs is to use PVA support on a second extruder.

 

These last 2 issues depend on something:

Did you model the part hollow in cad?  Or did you just turn off infill and top/bottom surfaces?  Does it absolutely have to be hollow or are you just trying to save time?  If you are only trying to save time you should try "gradual infill steps" feature instead.  This will help support the structure so the overhangs are better.

[erind 0]

Thanks gr5

 

The overhangs aren't an issue, its the top surface I am having issues with.

 

It is modeled in Rhino and hollowed in Materialise Magics. It needs to be hollow as it will be a shell with an internal structure (190 parts total). I am using PVA on my second extruder (problems there too - but I will work those out).

Speed is important because of the number of prints - which is why I went for the .4 LH. While I understand it will print smoother with a smaller LH, I have printed these parts previously with an older version of CURA and did not have any issue. I saved the setting and I am in the middle of using old CURA now to see if I can achieve the same effect as a year ago - fingers crossed.

 

If the problem persists I will try the lower layer height, but I have the feeling it is more to do with the infill of the walls in the new CURA slicing than the height given it has worked previously.

[gr5 2,168]

53 minutes ago, erind said:

it is more to do with the infill of the walls

 

For many parts, Cura 15.X gives me a better looking result.

 

Pay particular attention to wall thickness and line widths (there's at least 4 line widths in the latest Cura but only one in 15.X) and make sure the wall is an exact integral of the line width (e.g. 0.8 and 1.6 for line_width/wall).

 

Anyway now that I understand better what you care about, there is discussion of your exact issue here and some settings to try:

https://github.com/ultimaker/cura/issues/2665

 

[erind 0]

UPDATE: 

Used CURA 2.7.0 and there were no issues at all. Obviously an issue with updates in the new CURA.

Will process all the files the old school (2017) way!