Heat creep with PLA or something else?

Help with printing with specific plastic filaments.
Biolumo
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Re: Heat creep with PLA or something else?

Post by Biolumo » Tue May 24, 2016 8:40 pm

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.
http://www.thingiverse.com/thing:1587110

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.
Last edited by Biolumo on Wed May 25, 2016 9:05 pm, edited 1 time in total.

shellac
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Re: Heat creep with PLA or something else?

Post by shellac » Wed May 25, 2016 7:00 am

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

tom@hg
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Re: Heat creep with PLA or something else?

Post by tom@hg » Wed May 25, 2016 10:59 am

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.

tom@hg
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Re: Heat creep with PLA or something else?

Post by tom@hg » Wed May 25, 2016 11:59 am

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.

KelVarnson
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Re: Heat creep with PLA or something else?

Post by KelVarnson » Thu May 26, 2016 10:26 am

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.

Biolumo
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Re: Heat creep with PLA or something else?

Post by Biolumo » Sat Jun 04, 2016 10:15 pm

tom@hg wrote: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.
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?

kmanley57
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Re: Heat creep with PLA or something else?

Post by kmanley57 » Sun Jun 05, 2016 6:57 am

Biolumo wrote: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.
I will express my CRAZY ideas at any time! So you have been warned. None of my opinions are Lulzbots and can be wrong at any second.

killacycle
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Re: Heat creep with PLA or something else?

Post by killacycle » Sun Jun 05, 2016 9:51 am

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.

https://www.lulzbot.com/content/trouble ... per-motors

You simply can try a replacement motor for $13 :
https://www.lulzbot.com/store/parts/hal ... pper-motor

Bill D.

Biolumo
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Re: Heat creep with PLA or something else?

Post by Biolumo » Mon Jun 06, 2016 8:07 am

killacycle wrote: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.
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.

Biolumo
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Re: Heat creep with PLA or something else?

Post by Biolumo » Sun Jul 03, 2016 1:32 am

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
Image

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