Heat creep with PLA or something else?

We’ve been running our Taz5 for about 5 months now and have had a for the most part a pretty trouble-free experience printing countless parts of PLA. That is until recently when we started to notice some problems where longer (5+ hour) prints failed to complete. All the parts seem to show the same symptoms, the filament seems to become stuck in the hot end and the hobbed bolt just chews through the filament and fails the print. Here is a quick rundown of the actions we’ve taken so far:

  1. Updated firmware (no change)
  2. Measured resistance from thermistor (114 ohms) and heater cartridge (18.4 ohms)
  3. Performed several cold pulls, disassembled and cleaned nozzle (worked for one print, then problem reappeared)
  4. Updated to latest version of Cura (no change)
  5. Changed from Gizmodorks PLA to Village Plastics (no change)
  6. Replaced the “snail” fan with a 40mm fan and air duct, inspired by Taz6, see pic attached (no change)
  7. Mailed the whole printer back to Lulzbot who said there wasn’t a problem
  8. Tried printing parts in HIPS (success!)
  9. Bought and installed a new printer head (so far 8 hours into a 14 hour print it’s still going strong)

So it appears that the problem might be linked to our original print head and PLA - but how could this be, and why would it work fine for 5 months and then all the sudden appear on every long print? We really enjoy the PLA material so we’d hate to abandon it completely. Any help would be greatly appreciated!

I figure you’ve probably tried these, but just in case…

Adjust the idler tension, more or less might be needed

Dry the filament throughly

Increase temperature of the extruder, measure it to ensure it’s at least close to correct.

Lower the part cooling fan speed

Adjust the speed up or down a little

Disable retraction to see if that’s contributing

There’s also just not using so much PLA… I know it’s popular, but after using it, I like PETG, HIPS, and even ABS better for most things…

Check that the extruder and hotend are lined up. A misalignment can cause friction in filament path.

Try “seasoning” the hotend. Dip the filament in olive oil, re-thread and extrude. Search thingiverse for a filament oiler if this helps.

After typing that… if you’re comfortable disassembling the hotend, try soaking just the heatsink in SCIGRIP 4 (and a pipe cleaner) to clean the filament path.

I’m also fighting with heat creep on my mini, but not just on PLA, but on HIPS as well. printing slower seems to help, but at a certain height my filament comes out all cob-weby. I just designed my own 40mm fan mod similar to your picture. I actually just finished mine tonight. Mine will probably work, but just curious if your sharing the STL and/or solidworks files for your design.

Thanks for all the input so far!

We’ve adjusted pretty much all of those settings to no avail, we haven’t tried disabling retraction yet although I’m not sure if that would serve us in the long term.

This is something I’d like to look into next. The brand new print head worked like a charm on a 15 hour print, so I’m thinking something is gummed up on the inside. Are there any good tutorials on disassembly and reassembly of the hot end?

Thats a bummer. I’ve attached the file I used, just added a couple 4-40 heat sets to mount it up and then swapped the fan for a 40mm unit from Amazon. Functionally it works fine, but it did not solve my issues. Maybe you’ll have better luck.
Taz 5 Aux Fan Duct.STL (414 KB)

Undoubtedly this is heat creep, but the big question is why the 40mm fan with the duct on the heat sink didn’t fix it for you.

As far as the thing working fine new, and then going bad gradually, that’s exactly how it went with me. It could be attributed to the squirrel-cage fan getting weak over time, except your switch to the 40mm fan and duct would have fixed it instantly in your case, and it didn’t. The other thing that I think happens is that a buildup occurs inside of the filament tube, making it less effective at conducting heat away from the filament. You can see it under magnification.

I also think that if there is no thermal compound between the filament tube and the heatsink, there ought to be. I have not disassembled mine to the extent necessary to inspect for and add that, but I think it would make a huge difference in conducting heat away from the filament. Who knows, maybe it is there from the factory.

As far as giving up on PLA, there are just too many reasons not to do that. Lack of warping, compatibility with PVA for support, no fumes, easy to remove from the bed, I could go on… I am a huge fan of PLA and I think it is worth some effort to get it to work.

In my case, going to a duct and fan on the extruder heatsink fixed the problem in 99% of my PLA prints:


I did have one episode of PLA heat creep since installing the fans, so I decided to also use my extruder body fan when printing PLA:


I am not positive that the extruder body fan is having a significant effect, but I think it may be, because it partially fixed the heat creep problem before I installed the ducted fans. Prior to that, I was dead in the water in terms of printing PLA.

Interesting read… sounds like you thought you nailed it and then the problem reared its ugly head again. It sounds like a thorough cleaning and realignment might be my first order of business, but if that doesn’t work then maybe just upgrade the entire hot end with the E3D v6. Have you tried that approach yet?

Thanks. Nice design. I’m testing out the one i designed on a large HIPS part as we speak. Here is the STL for my basic design. While mine is not as elegant as your design or the TAZ6 fan cover mine does have the benefit of not needing brass inserts. I just used my 3mm tap and use the same size screws that the rest of my mini uses. I’m working on improving it still like perhaps a lower lip to improve stability and mounting holes on top. My extruder came with two convenient holes just above the aluminum plate holding the hot end that i think i will use for my mounting holes. I already had a spare 40mm 5v fan lying around, so i didn’t need to order one.

So far so good. If it works i may eventually upload my design onto thingiverse. EDIT: My fan replacement seems to have eliminated heat creep on tall HIPS prints. Haven’t tested it on PLA yet. http://www.thingiverse.com/thing:1587110

As to the main discussion i too am a bit confused that did not fix your problem. However the properties of PLA is basically the same for heated corn starch which turns into dextrin. Dextrin is basically a natural glue, so i wouldn’t be surprised if PLA gunks up hot ends more than other filament. I like the fact that PLA is fully biodegradable and i would like to use it for some projects. Newer filaments like N-vent and Ngen sound compelling though as they are somewhat cheap, have no fumes, and are stronger than PLA and ABS (at least i think that’s what someone said). Don’t know if they are biodegradable though.

I also have read that the short Lulzbot version of the hexagon hotend is more prone to heat creep versus the standard long hexagon hot end or the E3D. So some of it may come to poor hot end design. But i’m not an expert and i’m just learning as i go.
Hexagon_fan_cover1.STL (93.5 KB)

Yes, that is pretty much true, you can see how confident I was by the name I gave the thread. :slight_smile:

Unfortunately it did rear its ugly head again. However, the good news is that the ducted fans appear to have very nearly completely solved the problem. I hesitate at saying “completely”, but I do think it is possible that the one hiccup I had was related to something else.

I think that’s a good approach, particularly with regard to the alignment. Most of the cold pulls I did when I was having heat creep issues showed a distinct “step” indentation right where the filament entered the brass bushing at the top of the filament tube. This step suggested that the filament was getting hung up on an edge. Better alignment obviously would help that. I also polished the opening of the brass bushing to remove the edge; it comes from the factory with a chamfered opening, I polished it to make it more of a radius. That did not solve my problem, but it might have helped, and it’s easy to do. I used a small sanding cord that I got from McMaster Carr, and sanded it longitudinally so as not to introduce perpendicular grooves that might create further drag on the filament.

Just thought i would add that my fan mod on my mini has helped reduce the heat creep on HIPS. I havn’t tried it on PLA yet.

I also wanted to specifically mention that in my design the airflow is restricted much more than i expected and air is actually escaping the wrong direction (so much so that i thought my fan was mounted backwards). As a potential fix i noticed other designs in thingiverse have a oval notch in their designs as well that i think is there to help air flow. Mine is rather snug to the hexagon. EDIT: Adding a notch might help air flow, but i think it also made my HIPS warping and curling issues worse, so i went back to a solid fan which seems to work much better than the blower fan ever did.

I would add that the slightest adjustment to the angle of the mini fan will cause/fix this issue as well.

Hmm… I guess we’re just not seeing the kind of results that everyone else is with their fan mods. I mean, not only are prints still failing with the new fan, but there is practically no appreciable difference between the before and after of the modification. Yesterday we disassembled and thoroughly cleaned the hot end, if that doesn’t help at least for a short time then I think the only option remaining is to replace the hot end entirely… especially since the new print head is working like a charm.

Also, its worth adding, after several rounds of emails and calls with the support team at Lulzbot, that you should use caution if you are regularly switching between types of filaments in your machine. I was told that PLA will “crystalize” over 240deg and “carbonize” over 250 and can gunk up the feeder at higher temperatures… not to mention that ABS and PLA don’t really play that well together. So if you’re regularly switching between filaments you should definitely get in the habit of disassembling and thoroughly cleaning or you’re gonna have a bad time.

I wonder if there is some issue with the thermistor? Like, the thermistor is telling the controller that the head temperature is correct, and it’s being displayed as correct, but it’s really not?

It’s kind of difficult to get an accurate measurement of nozzle temperature. You could just heat it up to the temperature that you want to use, and then try feeding a piece of filament manually from the top, with the idler disengaged. This would give you an idea of how much physical resistance the extruder has to overcome. It shouldn’t take a lot of force to get the filament to manually extrude, if the temperature is actually correct.

well it seems i spoke too soon. Still having problems. It must be something other than heat creep. I watched my nozzle carefully and it seems like the filaments is just not coming out regularly on taller prints. Not sure if this is an issue with the hobbed bolt not gripping the filament well or if i have a bad or undersized extruder motor. My extruder motor was making some strange sounds before, but i tried oiling it and the noise seems to have fixed itself. However i have the half-height stepper and I’ve noticed when i get this cob-web problem that the motor is extremely hot (near the point it could burn), not sure if that is normal. Compared to the y-axis motor which is almost moving as much, which is warm but not hot. I think stock mini’s use a full stepper motor in the extruder. If so, would that make a difference? Would a hot stepper motor loose steps?

I think it loses torque more than steps. If I tweak settings wrong I will see the extruder quit extruding and no filament comes out due to the motor heating up.

It is tough to tell whether you have a feed problem or a temperature problem. Could be either one.
If the extruder temperature is getting too low, then the feed will get difficult and the motor temperature will go up.

The fact that filament is not grinding and filling the hobbed bolt with sheared pieces of filament points towards a fault in the stepper motor (or the stepper driver circuitry) and points away from a temperature problem.


You simply can try a replacement motor for $13 :

Bill D.

Well, i added a 40mm fan mod a week or so ago and my prints improved so i think that eliminated any heat creep. But this is clearly a feed problem that i believe is related to using the wrong stepper motor. Basically if your stepper drivers provide too little power to your stepper your motor will loose steps. And if you provide too much power your motor will get super hot AND loose steps. Since i now found out the half-height stepper is only designed for use in a dual extruder and a firmware update to cut the stepper driver power in half this all makes sense now. The stepper driver is providing power for a full size stepper, but since i currently have a half-height stepper it is getting too much power.

So i’m going to buy a full size stepper immediately and hope that fixes my problems.

I just talked to Lulzbot support and they basically confirmed all that too.

So an update on my issues and trying to fix them. First was to replace the mini blower fan to eliminate suspected heat creep. That seemed to help at first but problems did come back. Then i found out i was incorrectly using a half-height stepper which was getting too much voltage and heating up and loosing steps. So replaced it with a full size nema 17 stepoer. Seemed to help at first, but problems came back. So the latest improvment was to replace my nozzle completley as it seemed partially cloged. That has helped dramatically and my printer is up and running again better than ever. Perhaps the PLA i used just gunked up my nozzle even after switching to hips. But replacing the nozzle helped a lot regardless. The other thing which may contribute is that little herring bone gear keeps coming loose. I have a potential fix for that coming up. I have modified the OpenSCAD file for it to now have two set screws one 90 degrees from the other. That should help eliminate those from coming loose. Im surprised it was not designed that way to begin with. I will post that upgrade soon on thingiverse and update this thread.

edit: here is the herringbone gear with double set-screws. http://www.thingiverse.com/thing:1656360