Hi All,
I’ve had an on-and-off problem with clogs and stripped filament with my TAZ 4 for quite a while. I’m using a hexagon hot end. One of the more recent things I’ve run into is what seems to be shreds of filament collecting in the hot end and gumming it up. I’ve attached a picture of what comes out of the hot end when I do a cold pull. Has anybody else seen this? What might be causing it? Seems like it accumulates over time, and after quite a few prints (usually I can print for a couple weeks before things start failing). Any ideas on how to prevent it? Thanks!
The jagged edges on the cold pull look like the normal teeth marked left by the hobbed bolt; however, the picture shows 2 pieces of filament. What is the second piece from?
As the teeth of the extruder grab the filament they do cause small shreds to come off the filament but those usually stay out of the extruder and make a mess around the hobbed both and idler.
When you experience a clog, how tight are the idler adjustment screws? If they feel loose, they have probably backed off over time and allowed the hobbed bolt to slip, causing more of those little shreds and terminating in a “clog” caused by the filament not being pressed into the liquifier.
The other piece is a thin bit that was jammed in the extruder next to the filament. It positioned over the normal teeth marks on the filalment. Not sure how better to explain this, but I’ve attached another picture that might help. Basically, it seems like this is building up inside the extruder to the point where it jams.
I have had problems with the idler screws loosening in the past, but that doesn’t seem to be an issue at this point, I’ve got them locked down.
couple more pics, not sure if this is helpful
What type of filament? Check that the hotend and extruder are aligned… a bend in the path may introduce friction that could require more force to push the filament through.
Could also try a drop of olive oil to help the filament pass through the hotend. Search “seasoning hotend” for more information.
That looks like you are skinning the outside of your filament off inside the extruder somehow? Or the roll has an issue with coming apart.
This is ABS filament. I think alignment of the hotend and extruder could be part of the issue. I’ve realigned them, so will see if that helps.
I don’t think the filament is coming apart or being skinned. I think there are shreds of filament from the hobbed bolt biting it that are getting worked down into the extruder. Over time they are building up.
My guess would be the spool of filament. ABS is pretty durable. Try a different spool if you have some handy. IC3D stuff should be pretty good… hopefully they stand behind their filament and offer to replace the spool.
The teeth marks are pretty visible on the filament. They should show, but not to that extent. Hopefully the re-alignment of extruder and hotend should help relieve any bends in the path…and allow you to lessen the idler tension. Basically, the idler just needs to provide enough tension to keep the filament clamped… the tension shouldn’t be so great that it can’t adjust to varying diameters of the filament.
For what it is worth, I have seen this issue on my TAZ. Unfortunately, I can’t remember exactly what I did to fix the issue.
The problem is that liquidized plastic is working its way back up the extruder. This may be due to several causes:
- Is your heat sink fan operating correctly? If it has stopped functioning the heat break will not function correctly.
What temperature are you extruding the ABS at? The hotter the plastic, the easier it is to flow somewhere besides the nozzle.
Have you correctly set the diameter of the filament in your slicer? If the diameter of the filament is larger than the slicer is set, you may be creating excessive pressure in the liquifier, causing it to find other means of escape.
That’s interesting… the diameter of the path through the hotend should be pretty close to the diameter of the filament… unless of course using 1.75 in a 3mm hotend. But the filament should be viscous enough that it can’t go back up the hotend.
The other thought is heat creep, the heatsink fan isn’t working as you pointed out, or isn’t effective. I like to point my heat sink blower down a bit (maybe 1-2mm) so that the air flow hits the lower most fins and end-block. Cooling these areas seem more important to me than cooling the upper fins.
Ideally, I think the filament should only be molten / liquified in the heater block and nozzle. The heat break and heat sink should keep the filament cool until the heater block. I think its possible to adjust the gap of the heat break. The printer kits lack the small wrench included in the hexagon kit to perform this adjustment.
Try pointing the blower down a bit. I’ve read that a piece of electrical tape from blower end to heatsink sides can make the cooling more effective also. Lastly, try one of the 30mm box fan adapters for the heatsink.
That’s interesting… the diameter of the path through the hotend should be pretty close to the diameter of the filament… unless of course using 1.75 in a 3mm hotend. But the filament should be viscous enough that it can’t go back up the hotend.
The diameter of the path through the hot end is 3mm. The filament is usually 2.85 +/- 0.05mm. That leaves 0.1 - 0.2mm gap. Plenty of room for liquified plastic, especially if the plastic is too hot.
I think its possible to adjust the gap of the heat break. The printer kits lack the small wrench included in the hexagon kit to perform this adjustment.
You need to be careful with this. The hot end is designed for the nozzle to basically jam against the heat break with the heater block acting like a coupling nut. If you leave a gap between the nozzle and the heat break, plastic will ooze from both the top and bottom of the heater block. It will also be much harder to clear and old color out of the hot end when changing filament.
The stock placement of the heat sink fan is more than adequate for the job. Pointing the fan down towards the heater block increases the potential for jams by over cooling the heater block. Wrapping electrical tape around the heat sink will probably prevent air from flowing through the heat sink because the tape will block the exhaust of hot air.
Liquified filament is thick… don’t think its travelling that far up the hotend… but I could be wrong.
You need to be careful with this. The hot end is designed for the nozzle to basically jam against the heat break with the heater block acting like a coupling nut. If you leave a gap between the nozzle and the heat break, plastic will ooze from both the top and bottom of the heater block. It will also be much harder to clear and old color out of the hot end when changing filament.
With the wrench, you’re not affecting the nozzle - heat break gap. It would move the complete lower system (heat break, heater block and nozzle). FWIW, I just tried on a spare nozzle… and while it can move the lower assembly, it’s intent is probably to hold the heat break to tighten the heater block/nozzle.
The stock placement of the heat sink fan is more than adequate for the job. Pointing the fan down towards the heater block increases the potential for jams by over cooling the heater block. Wrapping electrical tape around the heat sink will probably prevent air from flowing through the heat sink because the tape will block the exhaust of hot air.
You’re right the heat sink fan is fine for the job… with ABS. Search the forums for heat creep issues with PLA…
No one said to wrap the tape completely around the heatsink… only to the sides (leaving the back open) to guide airflow.
No one said to point the blower at the heater block. A 1mm downward angle will still make the blower hit just the heatsink (and the thicker end-block)… the lower side of the heatsink where it REALLY needs to be cooled.
Heated filament swells before it liquefies… therefore jamming in the heatbreak/heatsink. Don’t believe me… remove the nozzle with the hotend at temp, let the filament cool 5-10 degrees so that its solid - you’ll be able to push the filament through the heater block, but won’t be able to pull it back through the top. When you examine the pushed through filament the end is slightly swollen, cutting the end off by 5-10mm… allows it to be extracted through the hotend.
kcchen_00, I suspect that we are in that wonderful space where agreement is not a realistic outcome. 
I understand your points. Thank you for clarifying about the electrical tape.
I agree that at at the temperatures we use, plastic is fairly viscous. I also have experience with that same plastic oozing out of both ends of a heater block when the nozzle was not properly tightened. Since the gap on the threads is probably less than 0.1mm, I still believe that it is possible for the molten plastic to work its way back up the extruder. Don’t forget, auto retraction process would probably help that process, especially if the heat sink fan is not working properly.
In fact, that may be where my experience with this issue came from. When I first received my TAZ 5, I didn’t notice the color coding difference between the 5v heat sink fan and the 24v print fan. As a result, I fried the 5v fan. As a result, I had several frustrating print attempts that jammed because of heat creep up the hot end.
Lulzbot support quickly helped replace the fan once I figured out what happened and Lulzbot has changed the design of the connectors (1 connector vs. the 4 I have) since then.
I want to say I doubt the heat break tube is actually 3MM, otherwise a 3.01MM filament would not get through. 
Plus the heat break continues about halfway into the heat block so the filament is already expanding before it exits the tube and is now bigger from heat swell. (taken apart/built a ‘few’ hotends to know this.)
Also remember retraction pulls the viscous end back up into the tube. I fixed a Makerbot Gen 5 for a customer a few months ago due to melted filament narrowing the heat break tube and plugging it due to retracting of the filament. 
Hadn’t occurred to me that this might be caused by plastic flowing back up from the hot end. That actually makes a lot of sense.
I’ve had a periodic problems over the past year with clogs and the hobbed bolt stripping through the filament. That is why I’ve had the idler tension knobs tightened down pretty hard, hence the deep teeth marks. But maybe my problems are primarily a heat creep issue. I’m using the squirrel cage fan that came with the hot end, so maybe using something beefier will help.
This seems like an area that needs some significant design improvements. Seems like it is too sensitive of a balancing act to get just the right amount of cooling to keep the heat break at the right temp. Maybe a longer heat break would help with this? Maybe a thermistor on the heat break with feedback to control fan speed?
@geburges, Respectifully happy at this union.
On my MakerGear M2 there is a physical gap between the hotend and the bottom part of the extruder (PETG) nozzle. If you look carefully you can see the filament passing from that plastic nozzle into the hotend. No melted filament oozes out of that gap. The hole for the 1.75 filament is 2 mm through the entire extruder, and not an issue. With that air gap the M2 rarely has jams (no heat creep) and the extruder cooling fan could if one wanted, be turned off. Mine is still on because I just want that extra safety margin.
Hi All,
Thought I’d post an update on this issue, in case anybody else has these problems and runs across this thread. I have one model I’ve been trying to print that kept failing repeatedly, in the same manner as I described earlier. I was noticing while trying a print that the extruder was retracting the filiament repeatedly, and it finally clicked that this was chewing up the filament to the point where the extruder could no longer grab it. Once that happens, the hobbed bolt just chews the rest of the way through the filament.
I fiddled with retraction settings, lowered the retraction length to 1mm (it was 1.75) and raised the minimum travel to 5mm (it was 2). That immediately seems to have solved the problem with chewing through the filament … the print is almost completed successfully.
So it seems that retraction settings can have a significant effect if you run into problems with chewing through the filament.
I’m not sure if this is also related to the pictures of filament I posted earlier in this thread, but I’m wondering if the excessive retraction was just pulling molten plastic from the heat block up into the heat break.
Sorry for resurrecting this Zombie thread, but I think I’m running into the same problem with my new Mini and the hex head. It feels like there’s plastic jammed hard in the feed tube fairly high up. I’m unable to get it out by heating the head per the docs here https://www.lulzbot.com/unclogging-your-hot-end. When you guys run into this, how do you get the filament out? I’d rather not have to take the whole thing apart.
