Kossel mini Extrusion Problems

Recently I tried printing somethings on my new Kossel mini. Unfortunately I am having several issues with the extruder. From what I've seen my black PLA seems to melt at around 190C. Anything higher and it starts to pop, anything less and it's impossible to push through the hot end. However when i feed the filament through my bowden it has a very hard time extruding anything more than a dribble. The fastest I've been able to get it to extrude by is about 240 mm/min. Whenever i try to print something any larger than a simple 20 x 20 mm hollow square the extruder jams and the push fit connection on the hot end disconnects.





Before the push fit started slipping the bowden stuttered whenever the filament didn't extrude fast enough. I have the fan set to 100 out of 255 in Slicer. At this point im not sure where to start when calibrating the flow rate and feed rate. I tested the e-steps per mm and when i asked for 100 mm i got about 98. As far as i can tell i should be under extruding. Please let me know where to get started.

It looks like that fan is going to drop a lot of air on the heat block, as opposed to just the heatsink where it should be,and it may be causing temp to fall off once you start feeding. You might try to either angle it away from the block, or make a duct/mount . . . And 190 is the bottom end of the range for most PLA . . . I find mine runs best at 210, but in any case, check Thingiverse for temperature calibration test prints, and see what really works . . . .the popping may just be moisture, and running cooler is not hlw to resolce that . . .

- Tim

Hello,

As Tadawson says you can just ignore the popping for now.

The cause for hotend blocking can among many be the following:

1) There is a space between the heatbreak and the nozzle. As shown here:



2) Melted plastic gets into your teflon tube where it sets and blocks


3) The temperature is too low leading to "strange" hotend behavior


4) Foreign particles blocking nozzle - If your plastic is filled with moisture it could be poor quality and thus have particles.


5) Teflon tube being pushed backwards leaving a empty space that the plastic will fill and eventually block like 1.


For starters you should do the following:

a) Verify that your hotend is assembled correctly - Especially pay attention to the teflon pipe when you open it. Is it all the way down laying flush with the steel pipe? - Also completely clean the nozzle. You can clean it by burning out the plastic on your (gas) stow or gas burner and use a small wire to push through the hole, clean after. If you have a 0.5 or 0.6 drill I recommend to drill up your nozzle and buy a new one that you will use later. Commissioning is much easier with a big nozzle.
b) Increase hotend temperature to 210
c) Decrease retraction length to 0.5 and retraction speed to 20
d) Change you extruder power setting (small screw driver on the pot-meter) to the point where it skips steps on the stepper instead of grinding your filament.



IF your hotend is all metal and does not have this teflon pipe then a few steps are different so report back in that case.