Filament too fat for heat break?

Discussion in 'E3D-v6 and Lite6' started by Randseed, Apr 24, 2014.

  1. Randseed

    Randseed Member

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    I have several rolls of 1.75mm filament which previously had fed fine. After doing a major salvage operation after my last disaster, I hooked up a new heat sink to my existing hotend. I couldn't figure out why it wasn't feeding until I disassembled the thing. Filament will go through the heat sink with no issue. However, it won't go through the heat break.

    There was crap jammed in the heat break and I got it out. However, the heat break has too small an internal diameter to pass the filament. I looked at it very closely and if it's deformed it was symmetrically deformed, so I doubt that is it. Is the filament supposed to go through the canal in the heat break? Or is the heat break supposed to get hot and the plastic start melting in the middle of the heat sink?

    And yes, it's a 1.75mm heat break and 1.75mm filament. A 0.4mm spare nozzle I have snuggly passes the filament up to the nozzle head.
     
  2. Sanjay

    Sanjay Administrator
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    Can you measure the true diameter of the filament you are now struggling with? (Preferably with calipers) Brand/Type?

    The heat breaks are drilled to 2mm internal diameter - so they should pass filament that is truly 1.75mm with ease. We've tested stuff that is 1.85-1.90 in places without problems. Things start to go wrong when you exceed 1.90mm. The problem is worsened when the filament isn't perfectly straight and has kinks or sharp bends, or even worse with bulges.

    The top of the heat break (part that screws into the heatsink) is meant to remain cold, and as filament crosses the small reduced diameter section into the part that screws into the heater block it becomes hot and melts.

    Sanjay
     
  3. Randseed

    Randseed Member

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    Thanks, that's exactly what I needed. Looks like somehow the part got a bunch of ABS or something in it. I drilled it with an appropriately sized drill bit (5/64, I think) to get the crap out of it. Works fine now.
     
  4. Andy3D_TF

    Andy3D_TF Member

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    Sanjay,

    This sounds just like the "sheath" of filament that I describe in the thread on the jamming.... I think sometimes it let's slide the filament, other times it ends sticking to it and causing the plug... In this case it got left in there and once removed the previous filament would be too fine a fit to easily insert the new filament...

    I'm aware that the "reflow" of the filament back up between the tube (2mm) and the filament (1.75mm) is common to all extruders to more or less extent, and suppose that the length of that area is what causes more or less back-pressure on the extruder, up to the amount that the extruder cannot cope with - that this happens more with PLA as is stickier just shows that being stickier causes more pressure. The crucial problem then would be to reduce the area where this happens, or use a more powerful extruder to overcome this pressure zone (again, data from AirTrippers pressure gauge system would be very interesting). The difference in extruder set ups may also help explain why some have success with some methods and others not (the reduction in pressure obtained bettering the melt zone (oil, shortening bore)) may still not be enough for certain extruder set ups to get over).

    Cheers!
     

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