Head clean process sometimes ejects filament

I’m just getting started with my new Lulzbot Mini and have run into an issue where occasionally when it goes through the head cleaning process at the beginning of a print cycle it fully ejects the filament. I’ve noticed when this happens the green wheel (controlling the filament drive) rotates clockwise must faster and greater distance than it does when the issue does not occur.

So far I’ve been printing with MatterControl Touch printer controller and two different PLA’s. Interestingly I’ve seen this occur only with one of the spools which differs only in color but it may be a random occurrence.

I’m currently trying Cura to see if I have different results and so far I haven’t seen this sort of behavior although I’m having other problems with Cura in that the default extruder temperature profile for PLA in my opinion is way too high (220C) which is causing parts to be too soft while printing.

Does the Lulzbot Mini have firmware that is in control of the head cleaning and bed levelling process or are these processes controlled completely (and thus can differ) with different printer controller software?



I think I just found the answer to my question regarding the clean head process. I notice that Cura uses profiles (each material has a fine, medium, and normal profile) and if you look at the profiles (simple text ini files) I see that you provide GCODE for various parts of the print process and this is where the head cleaning gcode commands are.

So I guess this tells me that MatterControl Touch has a bug in the print cleaning process that I’m running into (or there is something wrong with the printer communication from it).


I just got my mini today, but I have had a Taz 5 since February. So I have just a little bit of experience with these printers. With my Taz 5 what would happen sometimes was I noticed the skirt wasn’t printing anymore before the print. It would go through the motions of the skirt, but no filament would be extruded. What I realized is that Cura, I only really use Cura, was retracting the filament after the end of a completed print. This happens with the mini too. It retracts the filament to keep it from oozing out during the cool down period until the hotend is at a temp that wont melt the filament. So with the mini it retracts once with the end of a print and then again right before the wipe function to keep from extruding filament on the wiping pad. The double retraction has led my mini not to print the skirt, because there wasn’t enough filament in the hotend. The solution that I use for this and for my Taz 5 is to simply get the extruder up to operating temperature and manually extrude some filament before the start of the print. This primes the extruder and ensures that the filament isn’t pulled back to far during the retraction before the wipe function.

Also, which version of Cura did you try to use? I am using 14.09 with my mini and it’s working fine. The preset temps for pla are 205 for the extruder and 60 for the bed. Has been working like a charm so far.This is my first experience with pla, I have only printed with hips on my Taz. This is some cheap no name pla that I bought from Micro Center. I am hoping not to have too many issues with it. So far so good. Hope this helps.

I’ve pretty much come to the same conclusion you have about double-retractions however I’m not sure that was what I was seeing when using MatterControl Touch. The fact that the printer doesn’t ‘remember’ where the filament is leads to a few other cases where an over-extract could occur such as canceling a print before the skirt is finished (specifically before the filament starts coming out of the hot-end). Now that I understand the process more I simply know to avoid this and do pretty much exactly what you do by making sure the filament is primed or retracted only slightly before hitting print.

What I noticed when I was using MatterControl Touch however was that when it would eject the filament completely from the extruder the gear was turning way faster than normal. It looks to me that the Gcode was the same for the wiping process in MatterControl vs Cura, but I’m not sure what controls the ‘speed’ of the extrusion retraction. It could be that this was only happening.

I’m using Cura 14.09 as well. I started off with MatterControl Touch because I wanted a ‘wireless printer controller solution’ but have come to realize that I really don’t need the tablet ‘on’ the printer as I always have my phone or tablet with me when I’m in front of it and I’m really liking using OctoPrint/OctoPi as a controller to allow the printer to be wirelessly connected. I’m using a combination of slicing on OctoPrint with Cura Engine 14.12 and slicing with Cura 14.09 on a PC then uploading the resulting Gcode to OctoPrint.

Thought I noticed that after updating to Cura v3.6.8 (Win 10) for my single nozzle Mini,the Nozzle Switch Retraction Distance has to be set to zero, or the startup code will retract the filament. The standard material settings for the material I’m using had this set to 16 mm, which nearly ejects the filament.

The problem went away when I set the distance to zero, but then came back shortly. So – ho help here, sorry.