If you have changed a cartridge in the 2nd Generation Cube, you've probably noticed that it can be pretty difficult to pull the filament back out of the head. Chances are, if you have experienced this, the cartridge you are trying to change was PLA.
PLA melts at a different temperature than ABS plastic. And, that means that it also solidifies at a lower temperature than ABS. And, THAT means that if the material is not thoroughly heated before having the mechanism back it out, it could cool too soon and break... causing a real clogging issue.
So, the unload strategy for the Cube when using PLA is to first drive the filament DOWN into the heating tip, bring the temperature up and only then reverse the gears to start backing the PLA UP and out.
But, the current LCD message we get does not accurately reflect that timing reality.
It tells us to pull NOW... putting us into a tug of war with the Cube.
My fight with the filament gear has been almost comical as I've dutifully followed the message to pull up on the filament while the filament gear is obviously trying to eat the filament! Not one to avoid a fight, I've even tried using some pliers to exert my will over the seemingly recalcitrant Cube... to no avail!
Now I know what is really happening and why.
It's simply a messaging and timing issue. Instead of immediately pulling, we can relax for a few minutes and let the Cube do its thing. We need to be "one with the Cube". And, that means that we should wait a bit before trying to pull the filament out of the print head.
But, how long? Since the message on the LCD tell us to pull up right away, we need some clues as to when we should actually begin pulling up on the filament.
Sharpie to the Rescue!
What I now do is to make a little mark with a Sharpie on the filament just above the line where the filament enters the head. I then follow the direction of the mark to give me the clue as to when the filament is finally being reversed back out of the head. At first, it will be lowered into the filament channel for that extra heating we mentioned. But, once the heating step is completed, you'll see the mark rising up and back out of the filament channel.
That is the time to start pulling.
3D Systems has been great about changing the user messages on the LCD to make the operation of the Cube ever easier for users. Hopefully, we will see changes to the message concerning unloading so that we can simply wait for the appropriate message to tell us exactly when it's the right time to pull without fighting what is happening internally. That is the beauty of the Firmware update process.
In the meantime, the Sharpie is my friend. :)