Filament end expanding and seizing

Question

This is a continuation of this question where comments and answers were extremely helpful in diagnosing the issue, which I am still unable to solve.

I determined I have the problem shown in figure 3 on this question. How I confirmed that is I started a print and monitored it closely. As soon as the filament stopped coming out I paused the print and pulled out the filament - it looked like this:

I snipped the expanded part off and re-inserted the filament back in, hit resume print and it continued printing normally, except it had skipped a layer or two.

What I understand is there can be a few reasons for this problem:

1. Filament moving too fast and not being able to melt at the nozzle
2. Too much heat in the radiator block causes the filament to soften up and unable to be pushed by the incoming filament.

To combat case 1 I reduced the speed of the print using the knob down to 80 % which already felt like it is too slow, but that didn't seem to make a difference. I also tried printing at speeds of 85 %, 90 %, and 95 % as well and the problem occurred in all of them. So this leads me to believe that speed is probably not the issue.

I read that there could also be another thing causing case 1 and that is over-extrusion. To verify this I did the 100 mm extrusion test where I marked 0 mm and 100 mm and extruded 100 mm manually in steps of 0.1 mm. It took a while but eventually in the end I determined that it is under-extruding at 95 mm actual filament extruded which means there is less filament being pushed which should actually be working against the jam. I pulled the filament out after the test to see what it looks like and this was it:

Nevertheless, I adjusted my E-steps from 93 to 99 and repeated the 100 mm test again which this time was about 1 mm off (99 mm actual filament extruded) but I guess my markings could be off too so it should be good enough. I again checked the filament and it still had an expansion on the end.

At this point, I'm assuming that there is no issue with my extruder and print speed, so I'm on to case 2.

I tried printing at 180 °C but that had no effect.

I also tried printing without heating the bed as I read that could affect the cooling of the radiator as the fan will be blowing hot air, but that also didn't help and the filament seized.

I took the fan cover off and set the nozzle to 200 °C. After a few minutes, I measured the surface temperatures on the cooling block/radiator using a multimeter which showed 47 °C on the top-most fin and 65 °C on the bottom-most. I also tried reducing the nozzle to 180 °C and took measurements again which were pretty much the same with about a degree or 2 off. Ok so maybe something is fishy here because in this video you can see the temperatures he's reading are in the 35-40s range.

Just to confirm this was the problem I took quite a large home fan and directed it such that the stream is hitting the radiator from about 5 cm (this is while the hot end fan is not mounted with the screws but hanging on the side, which was also blowing at the radiator). I waited a couple of minutes and measured the temperatures again which this time showed 35 °C on the top and 50 °C on the bottom. That was as low as I could get it and the house fan was pretty strong. I extruded another 100 mm manually and this is what the filament looked like afterward:

It still had a blob on the end and I'm pretty confident given more time it would clog up again.

Honestly, at this point, I feel like I've put way too much time and effort into resolving this issue and that is frustrating me as I fail to see any results.

I'm even more confused by the fact that I have had a couple of 3h prints go flawless, then out of the blue, it starts doing this problem. Sometimes it doesn't happen, sometimes it happens 3-5 times per print. I had an 8h print which went very well until the last 30 min when it clogged, thankfully I was around and I did the snipping procedure so the print finished but it is visible where it skipped a bunch of layers and has a weak spot.

It is quite annoying to have to babysit the printer like that and I'm really reaching out to anyone who'd be able to help me.

Answer 1

This is classic heat creep. What's happening is that you're getting softened material up inside the 2.0-mm-inner-diameter PTFE tube, and then, because it's soft, some of the extruding force causes it to deform and expand outward rather than go through the nozzle, because that's the path of lesser resistance.

So, where is the heat creep coming from? In my experience it's not common on an Ender 3, but there are at least 3 fairly likely possibilities:

1. Ambient temperature in your printing space is sufficiently high (perhaps driven by bed temperature if the space is somewhat enclosed) to make the hotend cooling fan insufficient.

2. Hotend cooling fan is damaged or wearing out and running at severely decreased flow.

3. Your retraction length is way too long, and on each retraction, you're pulling up molten, or at least softened, material into the PTFE tube, then squeezing it as soon as you unretract.

It's possible to be a combination of these things. For example if your retraction length is too long, things might go okay until the air warms up from printing, then eventually get to a point where the added ambient warmth keeps the material soft just long enough for it to jam.

Some things that could help:

• Make sure you printing space is well-ventilated and air conditioned if ambient temperature is warm (I'd say over 26°C is bad for printing PLA). If you can't do that, run a desk fan pointed at the printer.

• Try lowering your retraction length, especially if it's over 6 mm now, but be sure to perform retraction tests (stringing tests) to make sure it's still sufficient.

• Use faster travel speed/acceleration and faster retract/unretract so that you're not giving time for heat to transfer from the retracted filament into the cold side during travel.

Given the temperatures you measured, though, I wouldn't be surprised though if you have a bad fan that needs replacement.

Answer 2

Try another filament. I have this happen with bad filament. Baking it helps, but not always and it reverts to bad filament pretty quickly after baking. So my last attempt printed fine after baking then started having this intermittent issue on the third print.

I'd try changing filament before blaming the printer.

Answer 3

Another way to approach this problem is to increase the temperature of the hot end and increase the temperature gradient of the heat sink (better heat sink cooling). One can increase the air flow of the heat sink fan or run fans to increase air flow around the printing bed and hot end, so that the air is cooler circulating through the heat sink.

Here's an overall approach: What are ways to avoid heat creep?