Hi marsius,
had the same problem.
This one is a nasty, multi faceted and multi level problem.
I guess you need at least address three different aspects to get rid of the cause.
Doing only one or two of them is not enough....
Welcome to the PLA FullMetal Hotend Jam Problem World.
You use PLA right?
I use the Bulldog XL with the Hexagon hotend on a Ordbot Hadron.
My conclusion of the problem cause is simple.
The heat of the nozzles crawls upward warming the filament on the way down.
As soon as it gets soft it widens up and sticks to the pipe wall.
The Bulldog tries to push it forward with all its might but fails to do so.
Instead it digs into the filament until it has no grip no more.
Even in the case the filament may move again its already to late by then.
It seems that this is a common problem with all full metal hot ends in the market, at least a plethory of posts around that problem indicates in that direction.
The solution for me was as follows:
1.) Add an additional fan to cool the area of the hotend right above the heating block.
The fan integrated in the standard bulldog mounting plate IMHO does not effectively cool the lower parts of the cold side of the hot end (transition zone).
2.) Reduce retract to at least 0.4 or even less (a friend switches retraction off completely with still quite good results) if your filament permits.
This one removes another cause of the problem (at least its probability to occure) with the same clogging effect.
3.) Put a drop of canola oil (zu Deutsch: Rapsöl) into the filament entry hole on the top of the hotend prior the first print of the day (or at least as soon as the problem occurs).
This one will prevent the sticking on the hotend walls (at least its probability to occure) and can easily be done by just removing the front plate of the bulldog (two screws) and a few centimeters of filament dipped into the oil..
From my point of view the MAJOR thing to do is to intensively cool the Hexagon and to reduce the retract a LOT.
So that additional fan might be 80% of the solution, and a retract of less then 0.5 removes 80% of the problem.
However using the oil will act as a emergency fall back in case something goes wrong though.
Together those three modifications/addons may solve the problem now and for ever.
To tell the whole story I have to add that I did some other things that might effect this problem as well.
Check your extruder steps and maximum feed rate.
You should stay safely within a range of max 8-10mm3/s of filament.
That comes down to a feedrate of around 3 for the extruder.
The defaults of the Repetier and Marlin firmware are way above that!! Adjust them!.
Adjust the settings in slic3r (or what ever you use) as well.
If you press to hard or to much the stuff will evade upwards and clog... doh.
I actually use the Marlin firmware now.
I had the feeling that Repetier has an issue with the extruder feed and retraction control.
But this was just a feeling during dozends of late night hours of watching and cleaning jams.
The main difference I recongnized was the amount of electronic 'noise' within the system using Repetier caused by the PWM temperature management of nozzle, bed and fans.
Together with a bit of too much power set for the stepper motors and to high speed and acceleration defined for the extruder could easily cause missed steps to the extruder stepper.
To few steps during retract will cause a too high pressure during restart of print. Stuff evades upwards.... you get the point.
If you have one use a Voltmeter to precisely adjust your stepper driver.
You should tune them to a reference voltage of 0.4V as a starting point.
I currently use 0.5V on all five steppers (double z driver) on my Ordbot Hadron (Makerslide aluminium build).
Beyond 0.6 will probably be to much. Take care!, those pots are quite tiny and from 0.4V to 0.5V you need to turn your ceramic! screwdriver just a couple of degrees.
Better not try to fiddle with those pots just by try and error or guts feelings...
Regarding motion parameters I currently use:
#define DEFAULT_MAX_FEEDRATE {800, 800,
3, 25} // (mm/sec)
#define DEFAULT_MAX_ACCELERATION {2000,2000,
100,2000} // X, Y, Z, E maximum start speed for accelerated moves.
#define DEFAULT_ACCELERATION 2000 // X, Y, Z and E max acceleration in mm/s^2 for printing moves.
#define DEFAULT_RETRACT_ACCELERATION
2000 // X, Y, Z and E max acceleration in mm/s^2 for retracts.
#define DEFAULT_XYJERK 10.0 // (mm/sec)
#define DEFAULT_ZJERK 0.4 // (mm/sec)
#define DEFAULT_EJERK
5.0 // (mm/sec)
Well, my Ordbot may print much faster than that.
However print quality is fine and it just works without hotend jams now.
Additionally from my experience, Marlin keeps the nozzle temperature easily within +/- 1 degree of the target temperature.
With Repetier the temperature was very often way (-5..-10) below target depending speed of filament extrusion.
Too cold a nozzel would raise the probability of clogging by a significant margin, beside other printing problems of course.
However Marlin is doing a very good job now with my equipment, even if its not as comfortable to setup and use as Repetier.
I'm sure that Repetier (or my rig) could be tweaked to be less noisy and/or error prone. Maybe I'll give it a try to check that out myself one day, cause I loved the Repetier comfort a lot....
For now I'm with Marlin. Never change a running system.... ;-)
The last advice I would shed is to set up a permanent oiling.
I simply put a small piece of spong, soaked with a few drops of canola oil, fixed with a little clip on the filament right on top of the bulldog, so that it could easily slide up and down.
This one provides for a constant thin layer of oil on the filament and additionally wipes of any dust or debris from the material prior entering the extruder.
The Bulldog easily copes with that little amount of grease. The teeth of the pully are sharp enough and the springs are strong enough to provide the required grip on the now slippy filament..
Guess this helps with the PLA specifc clogging of fullmetal hotends as well as general clogging caused by stray particels on the filament bigger than the nozzle diameter.
Since I use Marlin, an additional hotend fan, continuous filament oiling/cleaning and an extruder feedrate of 3... the problem did never occure again (three knocks on wood).
Wish you a happy end too!
Cheers
Harlekin
PS:
I would like to add a big big 'Thank You all' to the community!
NONE of the above given hints where grown on my fields.
I just did spend a lot of time digging through the internet, forums and wikis on the search for a solution.
All those cures can be found elsewhere. Credits have to go to those namless knowlegable original inventors, not to me.
Except one thing.
My change over to Marlin was my own Idea. However, I guess someone else had this Idea long since as well, somewhere....
I just did not find it prior it popped up in my mind as well.
;-)
Edit: Lots of typos...
Edited 8 time(s). Last edit at 07/22/2014 10:39AM by Harlekin.
