Heat creep with PLA or something else?

Help with printing with specific plastic filaments.
tom@hg
Posts: 6
Joined: Mon May 23, 2016 6:01 pm

Heat creep with PLA or something else?

Post by tom@hg » Mon May 23, 2016 6:41 pm

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!
Attachments
PRINT ISSUE.jpg
FAILED PRINT
FAN MOD.jpg
FAN MODIFICATION

ttabbal
Posts: 298
Joined: Wed Nov 11, 2015 4:20 pm

Re: Heat creep with PLA or something else?

Post by ttabbal » Mon May 23, 2016 7:14 pm

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...

kcchen_00
Posts: 1695
Joined: Thu Feb 19, 2015 12:42 am

Re: Heat creep with PLA or something else?

Post by kcchen_00 » Mon May 23, 2016 10:59 pm

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.

Biolumo
Posts: 205
Joined: Thu Dec 31, 2015 11:48 pm
Location: Loveland, Colorado

Re: Heat creep with PLA or something else?

Post by Biolumo » Tue May 24, 2016 12:42 am

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.

tom@hg
Posts: 6
Joined: Mon May 23, 2016 6:01 pm

Re: Heat creep with PLA or something else?

Post by tom@hg » Tue May 24, 2016 11:07 am

Thanks for all the input so far!
ttabbal wrote: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
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.
kcchen_00 wrote: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.
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?

tom@hg
Posts: 6
Joined: Mon May 23, 2016 6:01 pm

Re: Heat creep with PLA or something else?

Post by tom@hg » Tue May 24, 2016 11:15 am

Biolumo wrote: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.
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.
Attachments
Taz 5 Aux Fan Duct.STL
Fan Duct STL
(413.95 KiB) Downloaded 82 times

KelVarnson
Posts: 65
Joined: Thu Dec 03, 2015 10:03 pm

Re: Heat creep with PLA or something else?

Post by KelVarnson » Tue May 24, 2016 11:35 am

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:

viewtopic.php?f=36&t=4348

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:

viewtopic.php?f=29&t=4200

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.

tom@hg
Posts: 6
Joined: Mon May 23, 2016 6:01 pm

Re: Heat creep with PLA or something else?

Post by tom@hg » Tue May 24, 2016 12:37 pm

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?

Biolumo
Posts: 205
Joined: Thu Dec 31, 2015 11:48 pm
Location: Loveland, Colorado

Re: Heat creep with PLA or something else?

Post by Biolumo » Tue May 24, 2016 1:00 pm

tom@hg wrote:
Biolumo wrote: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.
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.
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.
Attachments
Hexagon_fan_cover1.STL
(93.54 KiB) Downloaded 81 times
Last edited by Biolumo on Tue May 24, 2016 7:46 pm, edited 1 time in total.

KelVarnson
Posts: 65
Joined: Thu Dec 03, 2015 10:03 pm

Re: Heat creep with PLA or something else?

Post by KelVarnson » Tue May 24, 2016 1:20 pm

tom@hg wrote:Interesting read... sounds like you thought you nailed it and then the problem reared its ugly head again.
Yes, that is pretty much true, you can see how confident I was by the name I gave the thread. :)

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.
tom@hg wrote: It sounds like a thorough cleaning and realignment might be my first order of business...
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.

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