filament feed problem - clog?

We have a mini we got for our high school student about a year ago, never had any issues with it. Just this week it stopped feeding filament – pictures attached.

I’m not sure how to diagnose, where to go from here. I tried adjusting the tension on the filament feeder, as well as changing the retraction speed. Nothing seems to matter, and nothing but a small dribble will ever come out of the hot end. Mostly it will just spin like its trying to retract, but never actually pull anything in, and after awhile digs mostly through the filament. The skate bearing there seems to move freely, and ive taken a small brush and cleaned out the feeding bolt grooves, all to no avail.

This is with ABS plastic, and I’ve tried a few spools - doesnt seem to make a difference. Also tried heating it hotter than normal with no success.

Any suggestions would be greatly appreciated, I don’t know what to try next to get this fixed?

Check that the tiny “blower” fan is running (the tiny fan pointed at the aluminum fins above the nozzle and heat block). If this fan fails or ingests something that stops it from spinning, the filament softens too high in the path and will kink/buckle which prevents extrusion.

The nozzle may be clogged. Has PLA also been in use? If so, that increases the possibility of a clog – since PLA can carbonize at higher temperatures and cause a nasty clog. Do some searches on how to do a “cold pull”, which is a way to clean the nozzle of minor clogs without disassembly. If it is a major clog, it may require disassembly or nozzle replacement.

It is also possible the thermistor is bad, saying the nozzle is hot enough to extrude when it really isn’t. That can be tested with a multimeter, by disconnecting the extruder and checking resistance on pins 17-18 (small red and black wires – see diagram for steps #5 and #6 at Resistance should measure approximately 100k Ohms.

Regarding tension, the washers should be about 7-8mm apart when filament is loaded and the idler is closed.

Thank you. Although, I just made matters worse… :slight_smile:

Fairly sure the fan is good - when I hold my finger over of it, it sounds like its ramping up…

There has been nothing but ABS in the machine, its all we buy.

I tried the cold pull a few times, and nothing happened. Based on a few online videos, I think I diagnosed the problem to be a clog all the way at the bottom in the nozzle. I followed directions to remove the nozzle, and thats where things went bad (see pic).

While twisting the nozzle off, it appears to have split – threads still in there.

Im now in “buy parts” mode, but don’t know what I need or what steps to follow? Any recommendations?

Thanks again…

Yikes… I don’t know if it’s possible to get the threaded portion out of the block without damaging it. (Maybe someone else will chime in with suggestions.) I’d probably buy a new Hexagon hot end, and rebuild the extruder.

You could also give Lulzbot support or itworks3d a call – they can offer parts, instructions, or (probably) even a per-hour repair service.

Yeah, I think I’m boned…

Looking at the prices online, it looks like I can get a hexagon hot end for almost $100 - and spend an entire day going through 30 odd steps trying to rebuilt it. Or I can spend $175 for a whole new head. I’m thinking the latter has a much higher chance of success, plus will increase my odds of remaining sane.

Looks like there is a v2.0 or a LulzBot Mini Single Extruder Tool Head v2.1. Any reason to not get the 2.1 seeing that its the same pricing?

I would have to recommend the v2.1 – it uses a standard 40mm fan for hotend cooling, which is more reliable than the tiny blower fans (I’ve had to replace 2 of the little blower fans). It also uses a newer stepper motor. I think those are the two main changes.

As for the old one… If unable to remove the rest of the nozzle, a new heat block and nozzle would be needed and those are only about $20. But there’s a fair bit of work to get the old block off (its set with high-temp thread locker), remove the heater core and thermistor, get the new block on (with new thread locker), and put everything back together.

So it will likely save cusswords to just buy a new one. But if you decide you want a “spare”, you might send an email to itworks3d and see what the repair cost would be on that old one. Between shipping/insurance both ways, the parts, and some labor – my guess is it would be about half the cost of a new toolhead.

Yes, you can try to remove the broken nozzle threaded part. There are/were some guides/steps to follow using a screw extractor on the forum.

Found it: