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Rossboss

Lattice Printing and Shell Gap

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Hello,

I have a UM3 and lately I've been printing components that consist of a tubular shell with a small period lattice structure inside of it. I've been running into a couple problems with them. As these components are for my work I cannot share the file but I have small sections of the current print below that should illustrate my problems. As these are multiple day prints I hope to fix these problems before the next iteration of the component without much more trial and error.

For one, the shell itself contains layers that did not seem to print. After running through the setting descriptions, it sounds to me like the fix for this not checking the 'Ignore Small Z Gaps'. From what the picture shows, does this seem like the correct course of action?

The other issue is that on the periodic layers where the lattice converges on itself resulting in many discontinuous vertices (the layer in the picture), there seems to be an extremely high degree of filament looping (not sure on nomenclature there) and vertical stringing. I think part of the problem could be that I have exceeded the Maximum Retraction Count threshold so the extruder lifts and moves to the next vertex without retracting the filament after a certain number of vertices have been printed. But even when it is under that threshold and it is clearly retracting the filament, I'm getting a lot of thin upward stringing still. So if my assumptions are correct I guess my questions are 1) how far can I push the Maximum Retraction Count threshold without grinding up the filament? and 2) how do I reduce that stringing in general? (I've seen the Ultimaker/Cura guide on reducing stringing but some of it seems outdated for the UM3. What are the UM3 setting thresholds that can reduce it?).

ZGap_FilamentLoops.thumb.jpg.e5313fd809ce6b90314b0cafd87cc8a0.jpg

ZGap_FilamentLoops.thumb.jpg.e5313fd809ce6b90314b0cafd87cc8a0.jpg

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Make sure you check layer view first before any print so you can detect some of these problems. You can even go into CURA setings and have it show one layer at a time to see the missing outer walls.

Look at this after every change you make to try and resolve it. I normally leave it in layer view in the problem area and make changes till you see its corrected.

I would first check Xray mode to see if any errors in the model and rule that out as an issue.

You may need to turn off all of the mesh fix options if your model looks good.

The retract count thing can be a double edge sword. You can have heaps and heaps of retractions without grinding if the speed is low.

but to remove the vertical string your getting you need the retractions fast. I had same issue recently and set it to 45mm/s

Cura 2.4 has Z-hop set quite high which is good for some things but i think you can get away with 0.4 or even turn it off.

To also reduce stringing you may need to drop your temp 5 to 10 deg.

Enabling coasting is also another method but not something i presonall have experimented with.

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So I have thoroughly gone through the X-ray and layer view (single layer at a time) and have seen absolutely no gaps in the layers or other errors. You said you recommend disabling all mesh fix options? Even the ones that seem irrelevant to this scenario?

Edited by Guest

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if your model is all good then you don't need any. Sometimes they can prevent things that you want.

If layer view shows everything is ok then you don't need to turn them off.

So did you make changes to correct any issues or does it look fine in layer view but your prints are not good?

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if your model is all good then you don't need any. Sometimes they can prevent things that you want.

If layer view shows everything is ok then you don't need to turn them off.

So did you make changes to correct any issues or does it look fine in layer view but your prints are not good?

I have not made any changes and it looks fine in layer view but the last two prints have come up with the same problems.

The common denominator is the smaller period lattice integrated into the tube so that says to me it is something with the file but there are no signs of anything wrong.

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The two pictures below are representative of the extremes in the lattice geometry; straight parallel sections and crossed sections. The crossed sections are where the looping problem is obviously but it is unclear if there is a correlation to the issue with the outer shell at these layers as well.

The tube diameter is 2 inches and wall thickness is 1.25mm. The lattice XY wall thickness is hard to say because it morphs as it goes up the z direction but it is very thin in the straight parallel sections. There are clear holes in the lattice wall but those I am less concerned about those since we perform an epoxy process on the parts after to seal holes.

Several softwares are used including Solidthinking-Evolve, Blender, and Materialise-Magics. The STL goes through polygon fixing process in Magics to fix bad edges and noise shells, overlaps and intersections.

5a33279de310d_EGRCSLayer.thumb.jpg.b80b5039a5f28ed7b42433174603e8f4.jpg

5a33279e0c007_EGRCXLayer.thumb.jpg.b80a41d353b7f83fff81919784683611.jpg

Edited by Guest

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Or does the fact that the wall thickness is not a multiple of the line width perhaps cause problems? I wouldn't think so because its only on some layers and not others but perhaps the lattice converges at certain points on the wall and changes the effective wall thickness?

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