Why is there a "dotted line" in my "larger" prints

Question

For some reason, my larger prints, or rather the ones that I create, have this "dotted" line in them. And, that line usually splits into two pieces.

I use Ultimaker Cura for a slicer, I use Blender for modeling, and I have an Ender 3 Pro

Let me know if anyone knows the reason for this as it's preventing me from making things on my own.

Picture:

Here's my Cura file, if anyone needs it

Answer 1

If hardware failures have been excluded (and they can be as subtle as "a broken wire only loses contact at this particular Z height", so don't be too quick to assume that), then the likely reason for a problem like this is bad geometry.

When you move from Blender to Cura, Blender exports a triangle mesh, which defines surfaces. Cura then has to read that triangle mesh and figure out which volumes should be filled with plastic. In order to do this reliably, the triangle mesh needs to completely enclose a volume (“be watertight” in the jargon), but it's easy for 3D tools meant for graphics (such as Blender) to produce models which

• don't completely enclose a volume, but have small gaps,
• have triangles that intersect but not at their vertices, or
• have parts that intersect other parts.

If any of these cases occurs, then the slicer may get confused about what the interior and exterior of the model is, and produce incorrect layers.

I'm not familiar with the functionality of Cura (I use PrusaSlicer), but if I had this problem, what I would want to do is look at the preview of the extrusions, inspecting it layer-by-layer to see if the place where the physical error is also has missing extrusion lines in the slicer's preview. If so, then this is almost certainly due to a geometry error in the mesh.

If this is the case, then to fix it, you could:

• Go back to Blender, find the bad area and edit it to be properly closed off.
• Or, use a separate repair tool intended to fix common mesh problems.

Answer 2

Blender is not to blame. You're drawing a wrong conclusion here. (as stated in a comment of yours)

From your Cura file, I extacted the 3d model as a STL file, and it looks like this:

Nothing wrong with it, it just a water tight triangulated mesh.

Cura produces a correct tool path, nothing remarkable there either.

The red marks on both pictures indicate where the infill lines meet the perimeter walls.

You can also see that the part is already really close to delaminating mid print on lower layers (all of the yellow marks indicate places where it looks like that layer tried to peel but eventually didn't fail to the same extent.

You should try to optimize the settings of your slicer in the (filament temperature, print speed, layer height, cooling) space.

Prusa slicer has a feature related to infill sticking to walls, called Length of the infill anchor:

https://help.prusa3d.com/en/article/infill_42 I didn't find a similar concept in Cura; maybe it could help for your setup, if nothing else works.

Also, you have elephant feet (bootom yello square bracket)

Answer 3

At first glance, this looks like it could be missing layers.

There are five possible causes for missing layers.

1. Something is off mechanically.
   Check to see if anything has slipped, shifted, moved, or popped out.
2. Misalignment
   Check to see that all three axes are properly aligned and haven't shifted. If there is any resistance, something is misaligned, bent, or a problem with the bearings.
3. Bad Bearings
   If a bearing is the culprit, it will make some noise. The bearing will also exhibit some uneven motion in the print head.
4. Lack of Lubrication
   Check to see if any of the axes are binding in any way. A little, and just a little, bit of sewing machine oil can be the solution.
5. Under-Extrusion
   This is a whole different set of problems that requires a new question to get an answer.

For more detailed information, see All3DP.com's article "3D Printing Troubleshooting All Common Problems"

Answer 4

This looks to me just like standard poor reliability of the Ender 3's stock extruder, which is ungeared (torque too low), poorly tensioned, and insufficiently grips the filament (due to flat hob whose teeth only touch the filament in a single point).

If you've had success with other models in the past, is is possible that they were more intricate shapes with small details? My guess is that you have the print speed set higher than your extruder can reliably deliver, but due to acceleration limits, the requested top speed was rarely or never achieved for the models you printed successfully. Now that you're trying to print something with long, straight lines, the toolhead does have time to accelerate to (or closer to) the requested speed.

You didn't mention what material you're printing. If it's PETG, you're just going to have to go a lot slower with the Ender 3's stock extruder. If it's PLA, you might be able to get it to work by increasing the temperature significantly (possibly a tradeoff with other problems). If the speeds you have to drop to for reliable printing end up not being acceptable, look at getting a decent extruder.