Hot end leakage and popping noises

So, loving my new Mini (when I have time to actually use it). But I’ve noticed something odd – with only about 15hrs of actual print time on the machine, my hot end heater block has developed a coating of what looks like melted/burned caramel. And during the first part of a print (usually during the perimeter/skirt phase), I’m getting a few small popping noises – like someone popping really tiny bubble wrap, or very small bubbles in chewing gum.

Now, from what I’ve read, popping noises like that are normally due to water absorbed into the filament. But this is a brand-new spool of Lulz HIPS that just came out of an airtight package with a dessicant packet, plus it’s been in a low-humidity environment since opening. And the pops only occur at the beginning of a print, not during.

As to the “caramel” leakage, I haven’t found anything searching the forum archives, but I’ve heard of some people having issues with PEEK liners (I think?) melting and leaking out through the threads of the hot end. Could this be what I’m seeing? So far, I’ve only used this one spool of HIPS in this printer, and only used the default Cura profile settings for the Mini – I haven’t tried any exotic filaments or experimented with any temperature settings.

The Mini has an all metal hot end so there is no peek in it to melt I am afraid.

Huh. Well, that makes things more puzzling yet. This “caramel” wasn’t present when I first unboxed the Mini, and from the look of it, it appears to be coming out of the threads above the heater block, before oozing down over the sides of the block. I don’t see how it could be the HIPS… so I’m frankly at a loss as to where it could be coming from.

I’m totally new to all of this but I recall reading somewhere else that popping noises during extrusion is usually from moisture in the filament. This coupled with the oozing might mean you got some bad filament. Just a thought.

I am getting the same popping noises, especially at the beginning like you. I don’t have any leakage or caramel on the hotend, but it has changed color a little. I think the popping is pretty normal as it happens even in PLA and all the people I know that print ABS have the same. I am getting some black crap in my natural filament from IC3D and its expensive…

I haven’t experienced any popping while using HIPS (my primary material), but I keep mine in sealed buckets with desiccant and have the luxury of a conditioned space with an RH around 45%.

While my Mini’s hot end is still clean, I have noticed that many users’ photos do show varying degrees of dark stains on the hot end. LulzBot does note that a surplus of thread lock should be used when assembling the hot end, but they also stop short of having it bleed over the top edge of the heater block. That said, if your Mini was fresh out of production, excess thread lock may not have fully cured and could flow when heated (the thread lock is aerobic so it cures inside the joint quickly, but slowly where exposed to air).

I believe I know what is making the popping noise you guys are hearing in the beginning, I get it too. I am using lulzbot hips so it is should not be a moisture thing.

When the hot end is heating up, before it cleans the nozzle it retracts several centimeters of filament. If you look at it you can see grooves in filament from the metal filament feeding gear. Now once it is done with autobed leveling and all that jazz, it refeeds the filament with the grooves cut into it. That may be causing small pockets of air to be pulled in and extruded with the filament. That is why the outline of the print isn’t always perfect and missing sections it has to refeed some of the filament it retracted for the nozzle cleaning step and that is when you hear the popping sounds. Hope my theory helps, just got my mini and am loving everything about it.

It’s getting worse over time. I dunno, this is still worrying me. Here’s a close-up photo…

https://goo.gl/photos/w7RmsogV8nT2WQjb6

Mine looks even worse than that, but I don’t think it’s an issue. It’s just the patina of use. If you think about it, that part of the printer is constantly exposed to fumes from the melted plastic, so it is natural that it will get a baked on residue. Kind of like how a well used not-nonstick cookie sheet gets a baked on discoloration from oils over time which in no way impairs its function.

That should be fine… as long as the leaking stops.

You can try to fashion a “q-tip” out of a piece of steel wool and a bamboo skewer to clean. Just heat up nozzle to the extrusion temp of the material. Should wipe off most of the material, but not the discoloration.

I haven’t figured out anything for the discoloration, but it doesn’t affect prints.

Carbonized filament on the heater block is fine since the heater block isn’t in touch with the print. Scrape any carbonized filament off the nozzle with a dental pick… A good soak in acetone (for ABS) will help the carbonized (black leftover) filament.


The most important thing is to keep the nozzle and area around opening clean. Otherwise any leftover material could “track” the extrusion away from the actual printed piece. Usually leaves hairs/spiderwebs or blobs on the surface.

Bronze wool is worth looking at. It doesn’t make fine splinters like steel wool does and it is softer than steel, so less likely to scratch the aluminum block or brass nozzle. It’s not quite as easy to find as steel wool – marine supply stores would almost certainly have it, some hardware stores too, and of course, there’s always the internet.

Well, it’s not a patina. After cleaning the head, I’ve been able to observe that, whatever the dark material is, it is emerging from the seam between the brass(?) extruder tip and the aluminum(?) heater block. And it appears to be a dark material, along with my filament plastic.

This can’t possibly be good.

You can try to tighten the nozzle… Heat the hotend to 250C, get two wrenches sized for the heater block (18mm) and nozzle (7mm) and give it a twist. The brass is soft, so don’t go crazy.

If the leak has stopped and the filmament is extruding relatively clean, I wouldn’t worry too much about it.

Worthwhile to contact support and send pictures if you haven’t done so…

I’d second kcchen’s advice. I recently changed my nozzle and I was surprised when I took the old one off that it took no force at all. I think the wiping process eventually loosens it. Checking it when the hot end is cold won’t mean anything because the frozen plastic makes it seem rigidly in place. But give it a try when it’s hot. Mine was so loose at temperature, that I could have removed it with only my fingers if I had fireproof skin. If it isn’t tight, perhaps the more volatile components of the filament can sort of ooze out. One other thing I had been noticing was that I could feel a catch when inserting filament, like it was hanging up on some ledge. After tightening to the 30 in pound setting, that catching disappeared. I figure my nozzle had descended some leaving a gap.

Just a word of warning about bronze or steel wool. Make sure you unplug your printer after heating up the nozzle. I forgot to do that recently and made a short between the heater or temp sensor which blew out an endstop controller. Had to replace the controller board as a result. Don’t be me. :wink: