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  1. #1
    3D Printer God(dess)
    Join Date
    Nov 2016
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    Lightbulb Salvage - PC4M5 fitting +Bonus

    For all the great efforts accomplished by great people on the board, I feel the need to dive into one of the smaller aspects of our efforts.

    If you've been playing with these printers for a while along with the little tube fittings, you noticed one annoying thing...
    These cheap PC4M5 fittings have a very nasty way of failing. The start of the failure is a simple turning of the tube...
    The PTFE tubing is rasped by the biting teeth inside the fitting.
    The newly created groove catches the gripping metal washer and rips it apart as you try with all your might to remove the tube.
    Next thing you know the tube won't stay in the fitting and the print you were working on fails.

    Sound familiar?

    First tip I will post is that if the tube is already stuck in the fitting, don't yank it out! Instead, find a pair of slender tweezers or appropriate needle nose pliers and pop the black cap off the fitting.


    The effort you put into removing the cap is about the level of pressure the fitting is capable of holding. The reason you can thwart this effort is that you are inducing a small angle which makes the cap come out easier. Do know that doing this can cause wear on the lip that holds these together. Meaning, yes, you can overdo this operation and the fitting's cap will be useless after a few times. However, with the cap removed, you can now remove the gripping washer by cutting off the end of the tube. But if you failed, or have fittings that have failed already, keep reading.

    I haven't figures out the best way for the layperson to do this, but here goes:

    I use a lathe with a through-hole drill chuck to make this simple groove in my tubing. Teflon cuts very easily and I'm sure we'll get some ideas on how to do this with common tools and/or a printed widget.

    The "top" of the groove, furthest from the end is ~7mm away. The groove is about 1.8mm wide.
    The depth is minimal, just enough to get a good edge.

    I had considered that I needed to put a c-tube in the groove (c-tube being a short tube with a groove along the edge). I did the following on a whim.

    Next I wrap the groove, neatly to start, with a 200mm length of bare copper wire 0.3mm in diameter. Direction doesn't matter but a reasonably tight wrap does.


    You can use different wire gauges and lengths but the outcome should be similar to this.

    ...put the black cap on from the other end of the tube...


    ...and stuff the fitting back together.

    It should look like this when you are done. Go ahead, pull-test the heck out of it. It isn't going anywhere. Worst case, the black cap will come out again. But that should be a whole lot more pressure than the printer will ever subject it to.


    Now for the bonus: Go ahead... twist it... I dare you! There is nothing left inside to rasp the tubing. Nothing left to wear out! Nothing to sphincter down the tube's ID!

    The reason this works is that the fitting has rubber inside. This conforms well to the knot of copper wire that remains. The copper wrap cannot easily expand either since stretching one loop will likely reduce another loops diameter. Essentially the tube is trapped by filling the groove.

    Can you carve a groove good enough with a hobby knife? Tube cutter? File? Post here if you have a success that should be shared.

    - - - - - - - - - -

    BTW: I don't consider this a solution on the hot-end simply because I want to keep that end removable for filament changes.

    If you have figured out a way to keep both ends of the Bowden tube fixed while changing filament, this solution would be great.
    The only way I can consider this is to put on a spool and forget about it until it is empty.
    Then taking the nozzle apart for the next spool is no big deal as it becomes a rare event.

    Pulling a filament all the way backward through the tube with the "bulb" on the end just doesn't make sense as it most likely will get stuck and then you have to undo one of these. Again, lifting out the cap is a limited operation as the hold will weaken.

  2. #2
    Administrator bolsoncerrado's Avatar
    Join Date
    Nov 2014
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    Aint something like this

    be more.... KISS?

  3. #3
    3D Printer God(dess)
    Join Date
    Nov 2016
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    Hahaha... not quiet. That only works if you didn't break the gripper washer first.

    What I am after here is a fixed tube to the fitting that is capable of rotating without self-destruction.

  4. #4
    Regular 3D Printer
    Join Date
    Jul 2017
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    what about E-Clips? Similar to the clip that bo suggested but this one is metal.

  5. #5
    3D Printer God(dess)
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    Nov 2016
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    The clip that Bo suggested is to keep the fitting locked.

    An e-clip of the appropriate size should work also. But you still need a clean groove to keep the Teflon from tearing.

    The wire wrap idea kind of opens this up to more people. Everyone has spare power cords, right?

    In the past I tried just threading a nut onto the tubing.
    But with Teflon's cold-flow characteristics, the Teflon tends to work that 60 degree angle of the threads.
    And with pressure on the tube, this actually made for a smaller ID over time.
    Plus think about what happens when you rotate the tube is the nut is fixed?



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