Grinding through PLA at a crazy rate

I was printing with HIPS and recently switched to PLA. The first few prints went fine but recently i’ve been having lots of problems with the filament grinding. I lose about 3 in every 4 prints due to it. Each time I clean the notched rod in the extruder to ensure all the grooves are clear and adjust the set screws to anywhere from the recommended 8mm gap to tighter, but most times I end up grinding a notch in the filament and losing the print.

I’ve been able to extrude by hand after it failed so it’s not a clog, i’ve even tried the “heat to 250, cool to 90, quickly pull out” to clear the nozzle of anything inside.

I’ve tried temperatures ranging from 190 to 210 with no luck. I usually get the first layer or 20 down, but not much past it. The filament is 3mm IC3D PLA, tried white, black and natural, all grind around the same rate.

Slicing using stock Cura settings for standard speed PLA.

What version of Taz are you running? The Taz 5’s small squirrel cage extruder cooling fan needs to be at 100% power to print PLA successfully. If it is starting to fail but still spins, sometimes you will have a little heat creep that causes a minor jam.

Does your part have a lot of retractions? If so, slow the retract speed to 5 or 10 mm/sec. and see if that helps.

When you extrude filament into air, does the extruded filament drop straight out of the nozzle or does it curl to one side. If it is curling, you might have a partial clog that causes enough back pressure to strip the filament.

Many things can cause problems with a PLA print. PLA is harder than HIPS and ABS so, you might need to tighten your extruder tension knobs a little more to get a good grip on the filament.

Some pictures of the stripped filament would help.

Thanks for your response:

  • I have a Taz5, only a few weeks old.
  • How do I measure the fan speed on the smaller extruder fan? The fan speed reported on the display and in octoprint is that of the main fan right? That reads 100%. I have confirmed it is spinning, but can’t confirm the speed. It’s very fast.
  • Seems to happen on parts with different amounts of retractions, I’ll try those new retraction speeds but i’m not sure this is the issue as the last print it failed on had fairly few retractions, a lot less than the prior print which didn’t fail (but was not quite as tall)
  • It sometimes curls when extruding into air after a fail but after a few mm of extrusion will start to drop down and coil on the bed, this could be the issue, i’ll do some more pulls to see if that helps
  • In testing I tightened the tension knobs to the point where the springs were 100% compressed, it didn’t help

So i’m going to do some pulls, try slower retractions, and increase the tension on the extruder tension knobs

The problem I have had with two of the small fans is that it is on and spinning but I would still get minor heat creep jams. Just enough to strip the filament but not so bad I couldn’t get the filament out of the extruder. Both of the problems I had were on new printers. The thing I noticed after I received the new fans is that they had a much higher pitched sound when running. I think some of the fans are partially DOA, just a little lame but still spinning enough to print hips and abs since those plastics don’t conduct heat as much as pla.

It sounds like you are checking and changing the appropriate things to troubleshoot the problem. Don’t hesitate to call lulzbot support and see if they have other suggestions.

Also, make sure the idler bearing on the extruder is spinning freely. If it is sticky, it can cause enough drag to strip the filament.

I have recently seen some hob bolts that are marginal and that will chew harder filaments like PLA. The hobbing should show a sharp edge and a good depth when looked at straight down on the side of the bolt.

Okay first off I have nothing intelligent nor pertinent to this matter but let me warn you the heat to 250, cool to 90, and quickly pull out, is not a reliable practice as my wife and I found out before we were married :slight_smile: just sayin

Sorry, it has been many years since I heard …‘QUICK PULL OUT’ it struck my funny bone

I like PLA also because it is said it is more environment friendly, but I also had to test several vendor and types. It looks like PLA can be very different. Please check other sources? Which PLA did you use? I use PLA here from a German vendor without a special brand.


PLA conducts heat a lot better than other materials, so what happens is that heat travels up the filament and causes it to swell right above the brass bushing in the extruder mounting plate. When this happens, the filament gets hung up and the drive bolt digs into the filament. At this point you are done, until you manually clear it.

If you look at the physical configuration of the heat sink as it relates to the extruder tube, you will see that it is doing next to nothing to actually cool the filament. The contact area between the heat sink and the metal filament tube is tiny, apparently by design. I’m not sure why it was designed like this, I have asked Lulzbot tech support on a couple different occasions to explain their design philosophy, but so far they have not given me any explanation. Perhaps I am misunderstanding the purpose of the heatsink altogether.

The bottom line of all of this is that more airflow on the heat sink will do very little to prevent heat creep. I put a second fan on it and it did not solve the problem, and in fact made no appreciable improvement. I also added slotted washers with heatsink compound in an effort to increase the surface area, and it did not help. I did these two things before I looked at the drawings for the heat sink and the filament tube and saw the very minimal contact area. After I saw this, the fact that they didn’t work made perfect sense.

PLA is a very desirable material for a number of reasons, particulalry low warpage and the ability to use PVA support. It is only for these reasons that I have invested a TON of time trying to make it work. I still have a couple things to try before I give up. If I have a breakthrough I will certainly post about it on this forum.

Print PLA at the lowest extrusion temp possible. Too high a temp, and the heat break and heatsink won’t work to keep the filament path cool.