What is wrong with this Lulzbot Mini print?


I’m pulling my hair out trying to figure out what is wrong with my Lulzbot Mini. I’ve just finished printing about 200 parts for a 5th and 6th grade after-school robotics course I’m teaching and have about 15 more parts to print but all of the sudden every print is failing at various layers with what looks to me like head clogging issues. I’ve tried several different filaments I have, I’ve cleaned the head, I’ve even replaced the extruder nib, and finally I replaced the entire extruder yet its still happening :frowning:

Any ideas?



Are you using the same stock barrel cooling fan? It looks like either bore lock due to heat creep, or an improperly pensioned idler arm. That or out of spec filament getting stuck. Could also be a failing thermistor but that wouldn’t tend to start mid print. Most likely is fan issue.

Stock fan which is operating correctly from what I can see and new thermistor when I replaced the whole hexagon head. I’ve tuned the idler as well and am using the printable tension jig. I’ve made hundreds of prints without issues previously. Im wondering if one of the steppers could be overheating or going bad?

I figured the failure pattern could be something easily recognizable.


The stock fan has a “partially working” failure mode. It spins but fails to move air. You are definitely having an extrusion issue, maybe check the small gear setscrew on the extrude, and check that it isn’t losing pushing force at the problem places which would indicate a motor short, but it looks like the fan or idler issue.

Directing a gentle airflow from a small fan at the printer while it is printing will help you diagnose the failing fan problem. Usually, the small fan will correct the problem if your hot end fan is starting to fail but still spins.

What type of plastic are you printing?

I’m printing with PLA.

Are you talking about the fan that cools the hexagon hotend going up to the feed or the fan that is blowing on the tip/printed-layer? I’m not sure I understand what the latter is for and thus are not sure how this can be causing the issue (unless your thinking the fan cooling the extruder fins is not working and I’m getting occasionally stuck feed due to heat-creep).


Which fan are you suspecting, the smaller one that cools the hexagon fins to avoid heat-creep or the larger one that is directed at the nib/printing-layer?

Can you explain more that small gear setscrew you mean? There is a set-screw that appears to connect the extruder fin-block to the heater block yet I’m not sure what its for - even on a new extruder end the two pieces don’t appear to come apart.


The small hexagon fin cooling fan is the one you want to be very suspicious of. The setscrew for the small gear is in the side of the actual small gear on the extrude motor shaft that turns the larger gear on the extrude that forces out plastic.

Thanks for the explanation. I checked the setscrew and its good and I have not witnessed the micro-blower ever ‘not’ spinning but I am suspecting that it is indeed not doing its job.

I’ve now witnessed the problem occurring first hand during a print: The hobbed bolt is turning, the tensioner is correctly set per Lulzbot and community recommendations, yet the filament is not feeding. At this time during the print the micro-blower fan was turning. During this time I un-latched the tensioner and found it took a little bit of manual force on the filament to get it to start flowing again at which point a bunch of PLA spuged out of the hot-end.

This is ‘heat-creep’ right? I suspect that the PLA is either expanding or getting tacky above the chamber and sticking to the walls.

What are the chances this has something to do with my PLA? I’ve tried several spools of PLA that I’ve printed just fine with in the past but during the course of diagnosing this issue (a couple of weeks) the spools have been out on the bench. Could this be a moisture absorption issue if the PLA has only been out a couple of weeks?

Has anyone seen a failure mode of the micro-blower were its turning but perhaps not at proper rates?

I find that the micro-blower is not available for purchase (perhaps out of stock?). Is there a replacement that anyone recommends?



I’m happy to say that with an external fan blowing on the entire printhead I’ve successfully made it through 4 prints. Even though when I witnessed the intermittent jam the micro-blower was spinning I can only imagine its not spinning at full force and is the cause of the issue.

Because the micro blower is currently unavailable, and because I no longer trust it I will likely replace it with another fan mounted to the front of the extruder.



Here’s a fan replacement shroud to mount a 25mmx25mmx10mm fan, replacing the original tiny fan, that was discussed in another thread about PLA heat creep problems. I put it on my Mini and haven’t had a problem since.


Hit this same problem recently on my year old Mini - turns out the fan had become rather clogged with dust and still spun, but hardly moved any air. I was able to partly clean it with a vacuum. It seems to have improved things, though I think I’ll also try the 25mm fan mod, or even maybe the taz6 style parts in devel.