Chimera/Kraken - How to fight blobbing?

Discussion in 'Multi-Extrusion' started by 626Pilot, Mar 11, 2016.

  1. 626Pilot

    626Pilot Member

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    blobs.jpg

    This is a calibration print done with a Chimera hot end. The copper filament prints fine. Then, it switches to the gold filament, and the copper filament oozes, causing the rat's nest on the left side of the print. When it goes back to printing in copper, the gold filament oozes.

    What settings should I be using for retraction, and retraction on toolchange? Is it necessary to drop the temperature on the inactive hot end, and then wait for it to come back up to temp later?
     
  2. Mike Kelly

    Mike Kelly Volunteer

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    An ooze guard can help, but it's not ideal. Depending on your extruder (which I'm guessing is an EZStruder by the looks of the bed) you could try forcing out the melt zone and doing a fast retract like on the bigbox.

    I use about 4mm of retraction during normal printing, then 10-15 for tool changes on my chimera. It's a good idea to print some like deprime test objects to calibrate retraction settings
     
  3. 626Pilot

    626Pilot Member

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    I figured out how to get it to run a little better and produce less mess. However, the solution is very bad for PLA.

    The design of current-gen E3D hot ends is such that if you retract more than about 5mm, it guarantees that the PLA will expand into the tiny crack between the heat break and heat sink, causing a jam. IMO, this is a bad design decision in the case of the Chimera and Kraken hot ends. It would have been better to ditch the separate heat break, and just make nozzles that pass all the way through the heater block into the heat sink. That way, there would be no tiny crevice for the PLA to expand into and jam. The Prometheus hot end is designed like this, and allows retracts in the 20mm range without jamming. I hope E3D considers making that design change in the next revision.

    The solution below will work, but it will also leave blobs that have to be cut/sanded off, ruining the finish and making the part ugly. (OK for parts that just have to function, but would never sell such a part to a customer.) Additionally, it will eventually ruin the PTC fitting on the hot end. My EZStruders have 5.18:1 planetary motors, so they can blast the blockage clear without any issue, but the pressure required to do this will slowly damage the PTC fitting. I had one blow out last week because of an un-clearable jam; the extruder just kept pushing until the fitting failed and the Bowden tube walked right out of the top of the hot end.

    This leaves me with a conundrum. I bought hardened steel nozzles to print carbon fiber/metal fill/etc., but those are all PLA hybrids. I have the Chimera, which can handle carbon fiber/metal fill just fine, but won't print without making a rat's nest; and then I have the Cyclops, which works perfectly (no stringing or mess), but would be reamed out and destroyed by those exotic filaments before I even got through a single reel.

    E3D, a little help? :)

    These settings might work OK with ABS, or perhaps PETG, but I don't know for sure.

    KISSlicer settings:

    Prime - 4mm @ 15mm/sec
    Retract - 4mm @ 15mm/sec
    Wipe - 10mm

    Select new extruder:
    ; Prime filament
    G92 E0
    G1 E10 F100
    G92 E0

    Cool & Retire Old Ext:
    ; Retract filament
    G92 E0
    G1 E-10 F100
    G92 E0

    Support:
    Prime Pillar / Skirt / Wall - Short Wall (to last ext change)
    Inflate Raft & Prime Gap - 20mm​

    Even with these settings, there are occasions when the inactive hot end will "burp" a blob of plastic out. This is especially common when it does the long prime after tool change. The mechanical action of the filament busting through the block slams it down into the melt chamber, kicking a bunch of goop out of the nozzle. The nozzle can run into that later and cause further problems.

    I'm starting to think a multi-in, one-out hot end is the way to go, even though it means I can never print metal etc. filament with different support material. That's a real bummer.
     
    #3 626Pilot, Mar 12, 2016
    Last edited: Mar 12, 2016
  4. 626Pilot

    626Pilot Member

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    I have found some success with ABS and HIPS. Both are low-ooze and don't get hung up on the heat break during long retracts/primes. The nozzles do drag a little bit of plastic around - little flecks stuck to the side - so it is a little messy, but perhaps workable. I also tried PETG, and it didn't get hung up on priming, but it oozed too much.

    These are my settings so far.

    Before the print, I push some filament through both nozzles, then retract both by 10mm. This prevents the initial prime on both tools from leaving huge globs. The on-tool prime is 1.5mm shorter than the preceding retract in order to avoid globs as well.

    Material:
    Code:
    Prime=4, Suck=4, Wipe=10, vP=15, vS=15
    Printer G-code -> Select New Ext & Warm:
    Code:
    ; Select new extruder
    T<EXT+n>
    
    ; Warm it up (non-blocking)
    M104 S<TEMP>
    
    ; Warm it up (blocking)
    ;M109 S<TEMP>
    
    ; Prime filament
    G92 E0
    G1 E8.5 F150
    G92 E0
    Printer G-code -> Cool & Retire Old Ext:
    Code:
    ; Deselect the (same) extruder (usually to cool)
    M104 S<TEMP>
    
    ; You may want to retract some filament here
    ;G92 E0
    ;G1 F500 E-2.5
    ;G92 E0
    
    ; Retract filament
    G92 E0
    G1 E-10 F150
    G92 E0
    
     

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