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Help troubleshooting three clogs on internal bridge layers


Printer Model
Extruder Type
Clockwork 2
Cooling Type
As you'll hopefully see in the post below, I did my best to figure this out on my own and failed, so I come to all of you for ideas!

My printer is a Voron 2.4r2 with CW2 StealthBurner and a Rapido MK1. I’m printing Polymaker ASA on a spool that hasn’t given me any grief thus far (I last printed with it a few days ago) and am slicing with Orca Slicer.

The build itself is fairly vanilla (totally stock other than the filter, bed fans, daylight, magnetic panel mounts, and CNC metal parts from Chaoticlab that were... surprisingly cheap at microcenter). It has and has about 700 hours on it, during which it's run through 4.1 km of filament. I would say that 75% of that was with ASA, 20% PETG, and 5% is TPU.

The photo below contains two of the three jams I’ve experienced in that time span. The first print failed on a very similar feature (internal bridge), but on a much much much smaller print. I’ve printed some pretty long (> 12 hour) parts on this printer with the same brand of filament, and similar settings, without issues although this is the first large “fairly normal polygon with big parallel faces” that I’ve tried to print.


For all three jams, I was able to release the extruder latch and pull the filament out of the heat brake. There was a blob at the bottom of the filament, which would be too big to get through the orifice in the heat brake (it’s a very snug fit on a Rapido). I suspect this is from sitting touching the heat brake for the remaining hour and 50 minutes in the print after the jam occurred. Note to self: install a filament run-out sensor…


There’s also always been a little bit of filament left in the hot end. The photo below is what came out after manually pushing it out with a metal rod I got with my i3 clone.


After the first clog on the small print, I reset and the print went off without a hitch. I didn’t think about it again until the top print above failed. I decided to swap nozzles just to be safe and bumped my extruder temp up from 230 to 240.

It looks like I might have been under extruding a tad on the third print and/or I need to tune pressure advance. The OG nozzle was plated brass, and I had recently tuned, so if it was starting to wear out then some minor under extrusion with a new/fresh nozzle makes sense.

Here’s what the slicer shows as happening on this layer. I am not showing the full layer so you can see it ends with the internal bridge on the lower left. There are a handful of retractions, but they’re not very frequent. There is no retraction at the end of the internal bridge before the travel to the start of the next layer.


The next layer starts perimeters first in the lower right hand corner. I don’t see evidence of the perimeters starting, so odds are the jam is happening between the two layers.

I have the slicer set to print nearly all features at the same speed, other than overhangs. This is potential correlation #1


I have the fan set to 40% with no cooling for the first 10 layers. However, for overhangs it’s going to 80%. This is potential correlation #2



Looking at a graph of what was going on with the extruder, it looks like all is (fairly) well here, at least from a temp perspective. The min PWM value might increase a hair for this layer, but without calculating the average and/or smoothing the line it’s hard to eyeball meaningfully. It does appear that the PWM falls off some once the jam occurs.


All three failures happened in the past month. Literally about a month ago, I changed three things:
  • Moved to Orca Slicer from SuperSlicer. I manually ported most, but not all, settings over (I'm sure I unintentionally missed some things)
  • Adding 2x bed fans to try to get my chamber temps up. I do not have a chamber thermistor installed yet, so I don't know what my temp actually is, but with a 350mm 2.4 with the stock Acrylic panels I doubt it's very high
  • I discovered that my Rapido was vibrating itself apart. I screwed it back together too tightly the first time, which crimped the end of the hot side the filament feeds into closed just enough to no longer let filament through. I was able to use the taper on a small tap to reverse the situation
Since then I've completed 25 prints. Most of these were sub hour prints, six were between 1 and 2 hours, and the two that most recently failed tapped out around the 5 hour mark.

So what do you think? Hot end? Potential wire flakiness in the chains? The extra cooling on that feature? The slower speed on that feature (and corresponding dip in flow)? Flakey filament? Something else entirely?
If it happens more often on longer prints it's probably heat creep. Maybe the fan connections need to be re-crimped.

Make sure you heat break is not bent or crooked.
Thanks for the reply.

The first time it happened was on a small/short (under 25 minute) print. I came back to a print that had no top layers. I can't remember if it had bridge fill, but if it did it didn't have very much since I could clearly see the infill in the majority of the part. I didn't bother preheating the chamber for this part due to how small it was.

What would I look for re: the fan connections to know whether or not they should be recrimped? Everything has been more or less untouched for the printer's life, minus disconnecting the all the hot end connectors once about 100 hours ago.

I really do wonder if it's the heat break... You may have missed it in my wall of text, but I did have to screw my rapido back together. In doing so, I did crimp the end of the heat brake closed slightly. I got it reopened with a punch, but maybe I didn't go far enough. Maybe this is why the new design advertises that "The inlet structure of the heartbreak tube is optimized to avoid the risk of deformation and plugging."

What my Rapido looked like after ~670 hours:

That little mishap is most likely the culprit. I did like the Rapido for a while but for me the heatbreak was too sensitive.
I started using bambu labs hotends since they are cheap and perform very well.
Just for grins, can you show the slicer view of that layer, with the view set to show the volumetric flow?
Just for grins, can you show the slicer view of that layer, with the view set to show the volumetric flow?

Here you go. It's a lot lower than the rest of the print due to a combination of speed (bridge) and line width (it looks like this might be top surface, which is 100%. Walls and bottom are 125%, infill is 150%).


That little mishap is most likely the culprit. I did like the Rapido for a while but for me the heatbreak was too sensitive.
I started using bambu labs hotends since they are cheap and perform very well.

What went sideways with the heat break on yours? Up until it vibrated itself apart and I over-tightened it, it was basically flawless. I'm somewhat tempted to grab the V2 since it looks like it resolves this problem. I'm going to give another go at widening the end of the hot side though. I already spread it apart to undo the crimp, no harm in going a bit further.
It's unfortunately from experience. 😁
I had an issue once where I had continual failures, but only on infill, and only with certain infill patterns. It was tough to narrow down, especially since my infill vs perimeter speeds were not significantly different. However, I had the "combine infill" enabled... so the layer height for infill was higher, causing a higher extrusion demand. My max volumetric limit was a bit too high, which I had never noticed before because with prior prints, the external geometry meant I was motion limited for speed (thereby reducing the volumetric flow needed), and the infill geometry was the same. Multiple layers of configurations/limits masking a lurking hidden issue.

It was only when I changed the infill pattern, to one that had less demands on the motion system, that the movement speeds could achieve high enough rates that the volumetric limit was reached. In my case, this would sometimes cause the stepper to skip - but also sometimes grind - and a prolonged over-extrusion attempt would grind away enough of the filament that it was game over for extrusion - it couldn't resume extruding even when it slowed down, because there was no longer any grip on the filament.
Womp womp. I've changed nothing but swapping to PETG and got failure much earlier in the print.

womp womp.jpg

I'll pull the hot end apart this weekend and ream out the cold side of the heat break more. I did order a v2 Rapdio, so I I might even bring some heat to this party. I'll be sure to post pictures of the process and outcome for those interested.

After cleaning out the hot end and reaming it out some, there was plenty of space where the old crimp was. I actually had to close the orifice back up some because the fit in the heat sync is... very tight.


To be safe, I lowered speed and bumped temperature with PETG and:


I removed the hot end while it still clogged this time and discovered that the clog was happening lower in the hot end. There is another small divot further down that tube, which might be contributing to the clog, but getting to it would require a 2mm diameter metal rod and I don't have one of those in stock.


In the meantime, the Rapido 2 showed up. I installed it with my v1 printhead prints and am up and running and clog free (so far). Wire routing is a bit tighter, but it fit with some minor persuasion. It looks like there's a v2 version of the printhead, but it would want me to disassemble the hot end. It looks like the wiring would wind up with similar bends anyway. I'll have to investigate whether or not the overall hot end length or nozzle location changed... If part cooling is unaffected, I'm tempted to leave it alone.