Thanks. Good advice. I cut the model down to just print a top surface already.
Damn PET-CF is still expensive though even with printing smaller test pieces 
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I typically LOVE this filament. I’d been printing hundreds of pieces in Bambu PET-CF for months before it went out of stock. As we sell these parts, I had to find an alternative and the Qidi-Tech always seems available (and cheaper). Upside was it’s blacker than Bambu’s version. Downside was I was getting more clogs with the .4 nozzle than I was with Bambu, so I had to switch to .6 finally, and dial everything in again. Print quality definitely not quite as “perfect” as the Bambu was with .4, but zero clogs since. When you get it right (which this is the first problem I’ve had with PET-CF), it’s hard to go back to PET-G or similar. It looks amazing.
Have always dried PET-CF and it’s very obvious when there is moisture in the filament. Bambu could never print “out of the bag”. Whereas Qidi-Tech can when I’ve been behind on orders. That said, I still dry at 70 deg C (max my dryer can do) for 10-12 hours, and print from a dry box.
Oh… one other thought to try out, slow the internal bridge speed way down. I think the default is 150% of the bridging speed. Slow it down to 20 mm/sec or slower. The idea is to give the filament more time to cool and bridge better.
Or you can cheat and just make a 2 or 3 mm section just below the top surface 100% infill. I’d bet that would work as a short term fix.
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Taking a sneak peak, I don’t think there’s any improvement.
What is baffling, is that none of the changes made (prior to even making this thread) or since, seem to be having any effect whatsoever. Which leads me towards hardware potentially?
Forgive my novice status (that’s the beauty of Bambu, you can get printing out of the box) … but I assume what we are really dealing with here, is “bridging”? Ie, a bridge over the infill preparing for the top surface layers. Am I understanding that correctly? If so, then doesn’t the part cooling fan have to kick in for those? And let’s say that’s failed, would that be typical of what I am seeing? I would assume it should report if the fan has failed, but I try not to assume anything.
Well, it’s pretty easy to test. You can turn it on from the console panel when the printer is otherwise finished and see if it runs.
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Yep, that’s it. But honestly, infill is generally tight enough for most filaments to bridge across with no problems. But note, most people wouldn’t consider this short distance a “bridge” per se. But in all honesty, it is.
What makes PET CF special (like PA, ABS, ASA, PC, etc.) is that these filaments don’t like to be cooled by fan. If you do, the bridging problem will go away but they will start warping. There may be a balance you can use, like 10-30% of the part cooling fan and still not warp, but that will take trial and error.
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I’m going to ask a silly question. Did you rule out the obvious? By that I mean did you take a brand new filament, verify that it was a different date code, break the shrink wrap and then dry it before printing?
I say that because this image here, is not due to bad settings. It is classic wet or bad filament. Your filament is not adhering at all in this image.
It wouldn’t be the first time that I saw a filament that was left out and then used after a week in high moisture or just a bad batch produce an image like that.
To paraphrase Occam’s Razor, “the simplest explanation is usually the best one.”
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The obvious and silly is definitely warranted at this point!
Yes, this was dried - this all started when I returned from a few days away and fired the roll that was already on the spool up again (having sit in an AC’d room but open for a few days). Results were as we see here. So I dried a new roll and off we went, the result being everything you see here in this thread since. But I take your point, and I’m about to check the drier is actually heating!
Last print was a complete fail (unsuprisingly). Pics attached. Again, it’s just the top layers that are no good (IMO). The rest looks typical of our usually good results.
Confirmed all the fans working as expected. Thanks for the tip on the console switches.
I edited a suggestion above. There is a setting for the “Internal Bridge” speed. Try knocking that way down. That’s the layer right above the infill. When you get that layer sorted out the top surface should follow.
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Taking your advice right now and just resliced… Just going to run full cals/flow dynamics etc first.
Well, if that’s the case, you explain it much better than the wiki does. The fan cooling section has got to be the most convoluted part of the entire slicer. Every time I read it it’s so interrelated that it’s like following the directions from that movie that goes like, " The pellet with the poison’s in the vessel with the pestle. The chalice from the palace has the brew that is true." 
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One might argue that there is a touch of improvement with the internal bridge speed knocked down to 20 mm/s. But I’m all out of ideas now other than waiting for a new spool to dry and giving that a go.
I’ve just never seen this problem before on any filament across 3 x Bambus even with known wet filament!
You finished all the orca calibrations already, and it’s still printing like that?
In that case, how about you try printing a benchy or some other calibration object that we’d all recognize and post a picture of that? There’s enough collective experience with those commonplace calibration objects that maybe someone will recognize a fundamental issue that hasn’t yet been articulated.
If that still doesn’t help, then I’ve got the “nuclear option” for you, but let’s all have a look at your calibration objects before going down that path. It was recommended to me once by one of the wise people on this forum (maybe even someone here), and it worked for me.
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I still think a good stop gap will be to use rectilinear infill up to 40%. The idea is to make that gap smaller, so it can bridge it better.
Here is a look at 15% grid and 15% rectilinear. You can see how much tighter the pattern is.
This is the look of the rectilinear 40% pattern and with it, I think it’s clear why I think it should clean up the surface and only have light pillowing. I would still suggest slowing down the bridging layer as well. You can also start bumping up the cooling fan by 10-20%, while you are testing.
Oh… yet another setting that may help in the bridging is the “bridge flow” in the Quality tab. Knocking the flow down to .8 will improve the sag by depositing less filament.
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Well she might float, but she certainly ain’t going to win any awards in a boat show. Evidence of same problem, obviously.
I have no doubt it will help. I just find it odd that I should be chasing new settings to print something that has literally printed hundreds of times before. Is that common with firmware updates?
I will likely try this soon, but waiting on a new spool to finish drying to just rule that out entirely.
You raise a good point. I don’t know the answer to that, but your benchy does have that kind of “melted” look to it that seems to come with CF filament moisture being too high when I’ve seen pictures where it has been identified as the problem. I went looking for PET-CF example photos so that I could post a link, but I only found nylon photos, but you may want to do a search and see if you find a match for wet PET-CF photos to what you’re getting.
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