Slicing Advice Wanted: Missing Extrusions

[AbeFM 35]

Howdy!

 

I've got a direct drive IDEX printer giving me some random missing lines. In general it behaves well, I do not think I'm printing too fast....

 

But I'm getting skipped lined. It looked random, so I printed a second from the same g-code at got the same exact errors.

Reprint, same g-code:

 I see the same single missing line, the same double missing line in the part. Around the back I see the same thing - something is giving me consistent weak extrusion.

 

Finally, same settings but dropped the part in the bed to shave a couple hours of print time:

 

Similar but not identical.

 

 

In desperation, I made some towers hoping to have a cheaper/faster test:

 

Here I'm not seeing any skipping at all, they print fine. I have two lingering doubts:

 

1) Supports look weird, under-extruded perhaps? This happens to 1 or 2 per layer, but not across all supports. I suspect under-priming? But they don't look like holes, it looks like bad layer adhesion or terrible k-factor. Note: K-factor/Linear Advance is disabled in firmware.

 

2) Perhaps my small squares don't allow peak extrusion rates and I need more material per layer.

 

Does anyone have a suggestion for a good test print?? Similarly, any advice on how to fix my lines would be appreciated. Infill and inner walls are printing at 100 mm/s - that's 0.4 mm line width X 0.2 mm layer height X 100 mm/s print speed = 9.6 mm3/s. There's a possibility my anti-stringing temperatures of 194C are a problem, but I feel these are reasonable numbers.

 

More pics in full resolution at https://photos.app.goo.gl/rpEzfANQTtnrXHR89

 

Attached, find my project. Retest MirTop- retraction restart-CURA.zip

Thanks in advance everyone!!!

 

Edited August 20, 2019 by AbeFM

[Smithy 1,146]

1 hour ago, AbeFM said:

Infill and inner walls are printing at 100 mm/s - that's 0.4 mm line width X 0.2 mm layer height X 100 mm/s print speed = 9.6 mm3/s. There's a possibility my anti-stringing temperatures of 194C are a problem, but I feel these are reasonable numbers.

 

I would say you print a way too fast and too cold. So you should adjust these values first, before trying something else. 

Try your test print with 50mm/s and 200° and check the result. 9.6mm3 is a lot of material which has to be melted in only 1 sec.

 

[AbeFM 35]

Heh, I was just waiting for the printer to run that test while I checked the forums for replies. Thanks for the advice, I think it's reasonable. It generally seems ok, but I guess it could be temperamental.

 

I'm used to pushing 10-15 mm/s on the Prusa, but that's got E3D bits on it. These are direct drive and don't appear to be slipping, and I don't see missing lines nearly everywhere.

---------------------------

I raised the temps a few degrees, and a few more, and the start temps, and it eventually cleaned up. I was at low temps to prevent stringing, though more retraction seems to have helped. It seems to be working so I'm banging out a few test pieces.

 

It seemed pretty weird because a whole part would print with only a couple weak lines, and always in the same spot. What's up with that? I was printing at 194 Print, 190 Start - now I'm at 200/200.

[AbeFM 35]

It's WEIRD the temperatures did that, since it followed the model so closely... But it DID work.

 

Thanks for helping with that issue!!

[johnse 31]

I think the reason it happened in specific places was that you were right at the edge of what your printer could do and your model geometry probably kept the average actual speeds low enough that the flow could keep up, but in those few spots it had a long enough, fast enough stretch to use up the melted material and the flow couldn’t keep up.

 

I imagine that if you used those settings to print a large cube you’d see a lot more areas of under-extrusion.