Z seam is moving for no apparent reason

[Link 34]

Hi,

 

I am printing a basic cylinder and as can be seen from the image at a point near the top the z seam moves and the travels change despite the model being exactly the same over its length. I have tried every option of layer start position and z seam alignment and still at the same point on the model the the travels change and the seam moves. As said the model is the same the whole way up, just a simple cylinder with one flat side and infil.

 

I have also tried all versions of combing and again no change

 

any ideas @smartavionics or anyone else ?

 

thanks !

[burtoogle 513]

Hi @Link, could you please attach the project file? That helps a lot.

[Link 34]

thanks

UM2_hanger.3mf

[burtoogle 513]

Hi @Link, there's a few changes I would recommend:

 

1 - don't use the sharpest corner z-seam flavour - it rarely does what you want. Better would be to go for user-specified as this will tend to lock the z-seam into a corner.

 

2 - using an infill wall is OK but it looks like a bug that it always starts in the same location and doesn't match up with the z-seam of the walls. Personally, I never use an infill wall count > 0.

 

3 - I think the gyroid infill will produce better results for this model, I normally use the connect infill lines option which kinda gives you an infill wall that covers 50% of the infill perimeter. You could probably reduce the infill density to 10% and still have a stronger print than using the grid infill.

 

This picture shows the settings I changed. Hope this helps!

 

[Link 34]

As usual you nailed !, thank you Sir !

 

it seems to be a combination of the extra infil wall count and the seam not locking as you said when you pick sharpest corner. Removing the extra wall and setting the seam to user specified (even with grid infil) sorts the issue.

 

When you set the seam to user specified do you leave it to the default location it picks, rather than actually type co ordinates in ?

 

Thanks again

[burtoogle 513]

28 minutes ago, Link said:

When you set the seam to user specified do you leave it to the default location it picks, rather than actually type co ordinates in ?

 

I normally need to change the x/y values to steer the seam to where I want it. In this particular instance, the seam was positioned OK with the existing x/y values.

 

Incidentally, I usually check the Z Seam Relative box and then the x/y values are treated as offsets from the centre of the part's bounding box.

 

Edited February 13, 2019 by burtoogle

[Link 34]

many thanks - really useful 🙂

 

Are you aware of the sharpest corner issue being fixed ?

[burtoogle 513]

1 hour ago, Link said:

Are you aware of the sharpest corner issue being fixed ?

 

Not sure what you mean there. I'm not aware of there being an open issue on github related to the sharpest corner z-seam method.

 

It's probably working as intended and the real issue is that the sharpest corner on each layer of your model does not occur in the same x/y position. It only really works satisfactorily when the model is suitable (no tiny jagged edges and a uniquely identifiable corner). Perhaps it would work better if the outline was smoothed?

Edited February 14, 2019 by burtoogle

[Link 34]

4 hours ago, smartavionics said:

 

Not sure what you mean there. I'm not aware of there being an open issue on github related to the sharpest corner z-seam method.

 

It's probably working as intended and the real issue is that the sharpest corner on each layer of your model does not occur in the same x/y position. It only really works satisfactorily when the model is suitable (no tiny jagged edges and a uniquely identifiable corner). Perhaps it would work better if the outline was smoothed?

 

I have been experimenting with the 'sharpest corner' function and it doesn't work consistently on all models as you would expect, despite the corner not changing in the model the location for the seam moves (as seen in the original problem). Also when you manual set the location of the seam it results in much improved travel moves, Cura seems to be able to much more efficiently calculate its paths when you set the seam location. Using sharpest corning seems to make the whole model way more complicated for Cura to handle (or it would appear so)

[burtoogle 513]

I think the problem is simply that what looks like a smooth curved edge to the naked eye can actually have very sharp corners and so one of those tiny (but sharp) corners gets chosen to be the sharpest corner in a given outline rather than the corner you were hoping it would chose.

Edited February 14, 2019 by burtoogle

[Link 34]

could well be, there also seems to be the added complication of the extra infill wall throwing things out, with that enabled nothing seems to keep the seam aligned.

 

 

[burtoogle 513]

Yes, I think the start point of the extra infill wall not being aligned to the inner/outer walls is definitely a bug.

[Link 34]

I have nothiced something odd with infil, this tube is the same size all the way along its length for example but the infil seems to change is pattern slightly in different points for no apparent reason, this happens with all infil types pretty much. Any idea why this would be ?

[burtoogle 513]

Well, the model maybe looks uniform in cross section but, in reality, because it's made from lots of triangles, the shapes of the polygons that define where the walls, infill, etc. go varies with height. It only needs a small variation in outline to sometimes produce quite a different print.

 

Here's an image showing a few of the triangles in your model...