Why does my head keep grinding into my PLA?

I’ve tried loading it at all manner of feed tightness’s and it will always grind into it no matter what I do.

When is it grinding? When loading, or while printing? What printer? What toolhead?

Sometimes it’s as simple as you haven’t cut a 45 degree slant to the filament tip, so it is tough to get enough into the gear to start biting into the filament.

Usually this is filament jammed in the heatbreak, above the hot end. It’s too cold to melt completely, but was hot enough to swell up and get jammed in there, so it can’t get pushed back down either. The top end of the jammed filament usually gets chewed down to a tip that is slanted to match the extruder gear, so any filament coming down gets pushed to the side or just into the gear itself, and chewed up.

If you release the tension on the idler, you can usually get a 1.5mm hex key down to the jammed filament along the filament path. Combine that with putting the temp up about 15-20c above your usual print temp, and you can usually push the jammed filament down into the melt zone and clear the clog.

As for the initial cause - heatcreep in general, melting the filament in what should be the cold zone, or retraction too high, pulling molten filament into the cold zone, where it solidifies in a swollen state, and jams things up.

If this isn’t enough to help out, additional details are required.

While printing? Always
What printer? Lulzbot TAZPRO Dual Head
What toolhead? Dual Head toolhead #2

It loads just fine. Pushes material out just fine after loading. Will (sometimes) print the first layer without screwing up and stopping at yet another “filament #2 error”. Nothing I can do works to stop it from just grinding into the material. I am using a custom made spool holder but this didn’t cause any issues for well over 34 prints before that. Why now??? Do I need to disassemble it again?

There are many causes of filament jams, and Wrathernaut addressed one of the more common ones, heat creep. This is typically a combination of print speed, layer thickness and temperature, and mainly affect PLA. Basically the hob wheel is trying to push the filament into the extruder faster than the amount of “traction” it has on the filament. The tension of the idler (the thumbscrew adjustment on the E3D extruders) can play a minor role as well.

We had a customer who had purchased a TAZ 6 from us several years ago and it has been chugging along beautifully all day/night building production parts for them. The TAZ suddenly started getting intermittent filament jams. Since their Gcode had been working for thousands of builds over many years, we can rule out temperature, speed and layer thickness as the culprit.

I went up to their facility and replaced their nozzle with a brand new one and it solved their problem. Before I removed the old nozzle, I ran some ABS through it. After I got back to the shop, I immersed it in acetone for a couple days, then cleaned out the softened ABS with a toothpick. Low and behold, they had all kinds of debris in there, including fibers of the fabric of the products they manufacture, the fibers had become airborne and landed on the filament and then got pulled into the hot end. The debris was intermittently occluding the opening of the nozzle!

1 Like

The TAZ 6 Single Extruder responds very well to cold pulls with cleaning filament (do a google search for 2.85mm). You can use the filament you are printing with but it doesn’t work as well, IMO.

So I do need to replace the nozzle and clean it out again. What happened to your customer is EXACTLY WHAT IS HAPPENING TO ME. Lucky we have another dual head. I’ll swap it out and clean the dirty one.
What things can cause heat creep?

A Cold pull sounds near impossible with the direct drive extruder. I can’t even yank the material out without the “unload” command running.

Sorry, I missed that you have the TAZ Pro tool head and responded to the TAZ 6 reference.

As for causes of heat creep, it occurs when the cold side of the extruder gets hot enough to start melting the filament before it gets to the hot side of the extruder. Another cause can be retractions of hot filament into the cold side.

For the first case, lowering the temperature of the nozzle can reduce the amount of heat the cold side cooling fan has to dissipate. Of course, you can’t lower the temperature too much or the filament won’t melt and flow correctly. Its a balancing act.

For the second case, reducing the retraction amount can prevent partially melted filament from being drawn back into the cold side when it can be cooled enough to cause a jam. Again, retraction is used to keep the filament from oozing out of the nozzle when the nozzle is being moved. If you reduce the retraction too much, you get blobs and zits in the object you are printing.

PLA loves cooling. I have added an external cooling fan to the frame of my TAZ 6 to make sure the air the cooling fan on the extruder is pulling in is as cool as possible. At first this fan was manually controlled but I found that it needed to be off for the first layer and then turned on for the other layers. Same with the part cooling fan controlled by M106.

I have a Raspberry Pi running OctoPrint connected to my printer so I added some hardware to the RPi and wrote an OctoPrint plugin to mirror the M106 fan speed.to my external fan.

So you’re saying if I’m printing with PLA In should try to keep it cooled as much as possible after the 1st layer?

What Wrathernaut and b-morgan are referring to is the filament upstream of the heat break getting too warm and softening. When it is pushed through the filament guide it expands from being pushed and gets stuck in the filament guide above the heat break. This is a different situation than I was describing where debris was occluding the opening of the nozzle.

Important note! Lulzbot does not sell replacement nozzles because a user can bugger things up pretty good if the nozzle is installed incorrectly. I had one customer break the nozzle off by over tightening it. Getting the threads out of the heat block was a huge PITA! Under tightening will result in molten plastic oozing out from the threads.

The nozzle must be loosened and tightened at or above your normal build temperature. I think E3D says like 290° or something but I feel that’s excessive, it works just fine around 10° above whatever your normal build temperature is. Use a 7mm box wrench for the nozzle, and either a 17mm open end wrench on the heat block, or you can use slip joint pliers in the larger opening position. When holding the heat block steady with either the wrench or pliers, be very careful to stay away from the electrical connections for the heater element and thermistor. After loosening the nozzle several turns, turn off the heat and let cool enough to touch to loosen the rest of the way. As I wrote above, I run some ABS through first so that it can be softened by immersing in acetone. After cleaning the nozzle, installation is the reverse of removal. At room temperature, start the nozzle by hand, then heat up and tighten the rest of the way. SUPER IMPORTANT: 30 inch pounds torque!

If you didnt get this fixed…my problem when printing was the default temp was 195…I print PLA between 220 and 225. I though it was gettting too hot and soft…it was actually to cold and could not push it through the nozzle. Once I heated it up it worked fine

I usually don’t have too many problems printing between 220c and 240c. I think when my ProDual has an aneurysm and just dives into a corner when trying to autolevel it permanently forced the bed to bend/incline in that direction. Now I have to give it a +.4 Z-Offset just to keep it from etching into the build plate on the left half.