Gaps in the top layer

[Smithy 1,144]

Again and again I have gaps in different objects in the top layer, but only when printing on my UM2Go

 

The result looks like this:

 

In Cura layer view, everything looks fine:

 

So I investigated several hours to solve the issue. What I have tried and done:

• Different object heights -> doesn't matter it is always the same
• Reduced speeds -> still the same
• Set extra skin wall count to 0 -> same result
• Set skin overlap percentage to 15% -> same result
• Set line width from 0.4 to 0.35 -> same result

 

Then I tried to print the same object on my UM2+ Extended -> looks good, no gaps!

Then I sliced the object with Simplify 3D -> looks good no gaps!

 

The interesting part is, that the wall count defaults to 2 on the Um2Go. When I print with only 2 walls then there are no gaps! But printing with 3 or 4 or 5 walls, there are gaps, every time.

 

Then I tried to create the Go in Cura with the UM2 profile, but same result as with the Go profile, gaps.

 

Next try, added the printer with the UM2+ profile and yes, no gaps. The difference between the UM2 and the UM2+ profile is the line width. UM2 defaults to 0.4 and UM2+ to 0.35. But printing with the UM2 profile and manually set 0.35 line width is also not working for me.

 

Now I also know why I only see it from time to time. I often print with defaults, so 2 walls and there are no gaps. But for some prints I need more walls and then I see the gaps.

 

Really strange issue....

 

If someone with a Um2Go is willing to try it, here is the project file: UM2GO_Guide.3mf

[Smithy 1,144]

So I think I solved the problem and found the root cause. After additional test prints and just changing a single setting with every print, I found that it is caused by the mixed speeds which is used by default. Just lowering the generic speed was not helpful, but equalizing all speeds to the same value did the job.

 

I was also wrong, that a 2 walls print and a print with the UM2+ Cura profile is good. They are much better, but under the magnifying glass I saw also very tiny gaps in these objects.

 

Anyway, it shows once again how important it is to adjust the speeds and not to rely on Cura's default calculation. With the UM3 and S5 I always do this, because otherwise I don't get dimensional accuracy. With the UM2 printers I have never needed this before.