Extrusion force

Discussion in 'E3D-v6 and Lite6' started by grat, Sep 15, 2014.

  1. grat

    grat Member

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    I've had a v6 (1.75mm bowden) for a couple months now, and I really like the kapton-less design, the ability to switch out nozzles, and the overall reliability of the head. As predicted, my PLA mount has been more than adequate, since the heat sink remains cool as long as the fan runs.

    I've produced some very nice prints, but I've also produced some really bad prints. First layer, and reliable extrusion speed have been my hobgoblins. If I lower the speed dramatically (25mm/sec for first layer, 50mm/sec for the rest), I can get quality output, but anything over that starts getting questionable. 60mm/sec seems to be absolute fastest I can lay down filament.

    I've tried both the 0.4mm nozzle and the 0.6mm (Where's the 0.5mm? :p), and I've made improvements to the extruder (better hobbed gear, drop micro-stepping to 8), and it's helped, but some filaments just Don't Like Printing.

    This weekend for comparison's sake, I installed my original J-Head (0.5mm), and it was immediately obvious that at the same temperatures as the E3d, the filament extrudes with far less force (half as much?) through the J-Head than it does through the E3D.

    Is this normal, or am I doing something wrong?
     
  2. elmoret

    elmoret Administrator

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    Did you update your thermistor between hotends? I doubt they both use Semitec 104GT2s.
     
  3. grat

    grat Member

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    Well-- By default, yes, the J-Head (MKV-BV) uses the semitec 104GT2. I had a different thermistor in mine because I'd broken the lead. As a result, when I installed the E3D, I did have to change the thermistor value in the firmware, and re-ran PID tuning.

    When I put the J-head back in, I was once again running a semitec 104GT2, although I haven't re-run PID tuning for the j-head, but the temperature was holding pretty steady (since I wasn't actually printing).

    Then for total paranoia, I hooked up the thermistor probe from my multi-meter (which has temperature settings) and measured temperature at the hot-end. The J-head was reading slightly high (reading 195, actual around 185).
     
  4. Jason_WI

    Jason_WI Member

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    The reason for the excessive extrusion force and slow printing requirements is due to the fact the nozzle temperature is some 50C cooler than the heat block. I posted this a few weeks ago here: viewtopic.php?f=13&t=238

    The aluminum heat block does not have enough thermal mass to maintain the nozzle temperature at high printing speeds. This is the problem with the V5 as well. The V5 to V6 heat block increased in size but it still is not enough.

    I also use a blower fan for cooling and the second the blower would turn on at layer 2 the nozzle temp would drop and cause a jam. I use a 3mm direct drive extruder with a gear reduced stepper which is capable of a lot of force.

    My solution to this problem was to make a heat block out of copper.

    http://i1161.photobucket.com/albums/q51 ... yi0kvm.jpg

    I haven't posted the new temperature charts with the copper heat block but the nozzle temperature is within 10C of the heat block temperature. My jamming problems are no more. I am getting consistant prints and no longer have to worry about 24 hour prints failing 23 hours in with a jam. My layer adhesion has improved as well. I can now run my blower at 40% with PLA and my temp holds on the nozzle. Printing overhangs and bridges without support are possible with the blower fan.

    The copper heat block is heavy and needs to be well supported at the mount.
     
  5. elmoret

    elmoret Administrator

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    Jason - unless you are starting and stopping a lot (spending as much time stopped as extruding), I doubt it is a thermal mass problem. The issue is more likely thermal conductivity - the thermal conductivity of copper is about twice that of aluminum.

    Copper has a specific heat (thermal mass) about 1/3rd that of copper, but it is about 3 times denser - further lending to the conductivity explanation, as by moving to a copper block you've not actually changed thermal mass.

    Other options are simply running the block hotter if you're at high flowrates, or using properly rated (~300C) thermal paste on the threads of the nozzle and heat break.
     
  6. Jason_WI

    Jason_WI Member

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    No stopping or starting here. My retract is .7mm.

    Call it what you want but my copper upgrade was the only solution to get the V6 to work.

    Here is my current print with red PLA. This is the Vend body on Thingiverse. 20% infill and no support. 25 hours in.

    http://i1161.photobucket.com/albums/q51 ... iwrgde.jpg
     

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