Filament grinding

General LulzBot TAZ
#1

I’ve had my Taz 6 for over a year and it’s been great. But lately anything I print that takes more then an hour or two fails due to the filiment getting ground away as it’s turned. I’d done a fair bit of searching and see this problem happen for mutliple reasons, but I can’t seem to nail down my problem.

I have tried mutliple different rolls and types of PLA.

I’ve done several cold pulls and disassembled the hot end to check for clogs. No clog found.

I have tried printing with the tensioner at various levels of tightness. I also checked to make sure that the bearing spins freely.

I had been experimenting with retraction settings, so I turned them way down. Still unsure of what settings changes I may have made incorrectly, I downloaded and started over with Cura lulzbot edition 3.2.21. Same problem. I next turned retraction off completely. Same problem.

Kind of at my wits end here. Any other suggestions?

#2

Filament grind is commonly seen if the overall print temperature is higher than necessary, especially with PLA because it likes a fair amount of cooling. It’s generally referred to as heat creep and basically what is happening is that the filament is heating up and softening along the length of the heat break until it reaches the hobbed bolt that pushes the filament through the toolhead. Then the hobbed bolt will just eat a chunk out of the side of the filament until there is nothing for it to grab and push. There are a few things that could be causing this if it is indeed heat creep. The first thing to check will be that the fan on the front of your toolhead that cools the heatsink is running, to do this just turn the printer off and back on keeping an eye on the fan to make sure it powers on with the machine. If that fan is turning on as expected you could try adding a small desk fan or possibly turning down your print temperature slightly. What brands of PLA have you tried? What settings were you using to print? Could you post a few photos of the filament removed from the toolhead after a failure, as well as some of the failed prints? There are some visual hints to the various causes for filament grind and getting a look at what things are coming out like should help narrow down what’s happening here.

#3

The fan does power on when I turn the machine on.

Doing a test now with the temperture turned down to 195. I use alot of Inland and Polymaker. See pictures below.

After starting over with the latest version of Cura and it’s base settings I tried a Rocktopus

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#4

Then I tried a smallish item that would take 4-5 hours to print.

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Success on both! Not perfect but not failures.

#5

So then I tried a very large item, something that would take 8 hours plus.

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Tried it twice as you can see. These failed about 1-2 hours in.

#6

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The purple pictured here is the polymaker, The gray is Inland. I have many other failed examples, but they basically look the same and came from many different rolls, as this problem seem to slowly …creep…up on me, and didn’t happen all the time, at first.

Also of note, In december I got a Printed Soild enclosure. I didn’t think it was part of the problem as I was printing fine for months. Just FYI.

I’m doing a test now, medium size item, 195 degrees, no enclosure.

#7

Latest test just failed. About an hour or two in. Left the enclosure off, printing at 195 degrees, and while I didn’t have a small fan to point at the printer, the room does have a ceiling fan going. I’ll see about bringing a small fan from work tomorrow.

Also, I opened up a brand new box of Inland brand PLA. To insure moisture isn’t part of the issue. But I do live in California, so humidity isn’t often a thing here.

#8

Are you using the stock settings aside from temperature or have you made other adjustments in addition to the experimenting with retractions you initially mentioned? Also since your other models all came out well I have to ask, have you tried a variety of larger models or have you just been experimenting with this particular model?

#9

That was why I downloaded the newest version of Cura lulzbot edition. I wondered if I had changed something and wanted to start fresh, to ensure that I did that I deleted everything and installed fresh. It was from that install and those stock settings I printed the items pictured above.

I’ve been experimenting with lots of different models. The same situation seems to persist, anything that takes 2 hours or more tends to fail like the above examples.

#10

Is there anything in the environment that may contribute to higher-than-expected temperatures around the extruder? What is the ambient temperature in the room by the printer?

Things to consider:

  • Is the printer in direct sunlight?
  • under or near a warm-air vent?
  • In an enclosure, a closet, or a very small room with little or no air circulation?

Preventing heat creep depends on that little fan blowing cool air on the extruder heat-sink, and if the air that it is blowing is warm enough, the printer may be working as designed but still be unable to keep the temperature of the extruder and filament low enough to prevent heat creep.

Edited to add: Consider this thought experiment – PLA has a glass transition temperature (the point where it softens) of about 140 degrees F (60 C). The goal is to keep the top of the heat sink below that temperature. If the ambient air temperature is 100 degrees F (in an enclosure, or closet, perhaps), then the differential between the air and the maximum temp is a paltry 40 degrees F. But, if the air temp is held at about room temperature (70 degrees F), that differential jumps up to 70 degrees – a considerable difference when cooling.

#11

Another factor is if you are printing a large object your cooling fan is pulling in air off the ‘warm’ bed, so you are actually blow about 50C air over the cold end. I use an downward angled cooling fan now to help with this issue myself.

#12

Sunlight? No, Warm air? I live in California, we use the heater once every 4 years. :slight_smile:
I do have an enclosure, but the problem still happens if I remove it.

Preventing heat creep depends on that little fan blowing cool air on the extruder heat-sink, and if the air that it is blowing is warm enough, the printer may be working as designed but still be unable to keep the temperature of the extruder and filament low enough to prevent heat creep.

Edited to add: Consider this thought experiment – PLA has a glass transition temperature (the point where it softens) of about 140 degrees F (60 C). The goal is to keep the top of the heat sink below that temperature. If the ambient air temperature is 100 degrees F (in an enclosure, or closet, perhaps), then the differential between the air and the maximum temp is a paltry 40 degrees F. But, if the air temp is held at about room temperature (70 degrees F), that differential jumps up to 70 degrees – a considerable difference when cooling.

Thanks for the unique explanation. The temperature has definitely been in the 70-80 degree range. We are having a bit of a heat wave. But, I’ve been having his problem for months now. Since the spring.

Question. Do these types of fans slow down instead of outright dying? I’ve put a few hundreds hours on this thing. Should I replace the fan?

#13

Oh that’s interesting. Did you print a mod to get this downward angle?

#14

I found it on thingiverse, and printed some out and changed all my extruders to use it last year.

https://www.thingiverse.com/thing:2417662

Your fan can be picking up little strands of filament and wrap them around the shaft of the fan, which over time as they build up slows the fan down.

#15

Cool thanks, i’ll give it a try.

#16

So, the print that failed most recently with the enclosure removed. I tried that print again with a fan pointed at the printer, it printed almost perfectly. (Tiny bit of stringing, but remember I turned off retraction completely)

#17

Back off on your flow rate a few percent.

One cause of filament grind is having your flow rate too high. I had this exact problem. Reduce your flow rate to the point where on your first layer each nozzle pass of filament just touches the one next to it.

If you overextrude, nozzle pressure builds up and the hobbed bolt is unable to push the filament forward, causing it to take a chunk out of the side of the filament.

Jim

#18

I’m experiencing something similar (see https://forum.lulzbot.com/t/prints-end-up-printing-in-air/6061/1). My prints end up “printing in air” and the filament in the hot end is chewed up. Not 100% sure if my issue is due to the filament getting grinded down and chewed up, but that does seem to be one of the issues.

#19

FWIW, another user (kmanley57) suggested that the issue was that the heat sink wasn’t getting cooled enough since it was inside an enclosure (great for ABS, but apparently not so much for PLA). I removed the top and the front panel of my enclosure, and PLA is now printing great again. I haven’t printed it yet, but I found a fan for the Taz 4 on thingiverse that cools both the print and the heat fins (https://www.thingiverse.com/thing:431185) and I’m going to give that a try as well.

Jeff

#20

I tried this. Default settings had it at 100% flow rate, so I went down to 95%. Still had a failure a few hours in.