Filament idler adjusting tension

Discussion in 'Build Help' started by Alex9779, Apr 9, 2016.

  1. Alex9779

    Alex9779 Moderator
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    I recently had issue with filament grinding and realized that my tensioning of the filament idler didn't work properly.

    So here it is how the whole thing is supposed to work and what went wrong on my machine.

    This is a cut through the upper print head with the filament idler tension mechanism which are only a screw, a square nut, a washer and a spring.
    I omitted the spring and the idler:
    Print heat cut.PNG

    If you remember the build or have a look at your machine the spring is squeezed between the washer and the square nut.
    Because the washer is not fixed on the screw the spring pushed against the washer.
    The washer then is under the idler and pushes the idler up what results in pressing the filament harder against the drive gear on the motor axis.
    You can then adjust the tension by turning the screw and compressing the spring between the washer and the square nut because the square nut moves upwards.

    For this to work properly the square nut has to move freely in the square hole.
    The tolerances seem to be quite good so on my stock part and on my parts I printed myself this was the case.

    The problem that came up was with the screw.
    You can see that the screw stand on the bottom of the hole and that all that works what I described above the screw has to turn freely in that hole.

    But in my case the hole had a too tight tolerance and the screw actually screwed in the hole going deeper and deeper through the material until, which is not quite far, it hits the motor mount screw right under it and was fixed.

    So I was not able to tighten the spring enough because I couldn't turn the screw any more. And because of that the square nut didn't move upwards like it is supposed to be to load the spring.

    Unfortunately the parts I used was now broken because the screw was not able to stand on the bottom of the hole anymore, I had to print a replacement.

    Wahn assembling the replacement I looked carefully that the squarest could move and that the screw did not screw into the hole. Actually I had to drill it a bit very carefully. I took a 4.5mm metal drill.
    Gotta be really careful not to break the bottom of the hole.

    Maybe it helps somebody else...
     
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  2. Ephemeris

    Ephemeris Well-Known Member

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    Interesting! Mine has never felt right. I may tear it down in light of your explanation. This is a good example of the currently incomplete instructions not explaining what things are supposed to do. Hard to troubleshoot things when you're not certain what they're supposed to do. Your explanation should be added! Thank you.


    UPDATE: Yes one of my square nuts was hung up near the top of its well so the spring length was not being adjusted. This is on a dual kit with factory printed parts.
     
    #2 Ephemeris, Apr 9, 2016
    Last edited: Apr 9, 2016
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  3. Alex9779

    Alex9779 Moderator
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    Glad you got it right now...
     
  4. Trevor

    Trevor Well-Known Member

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    Wonder if the 1.1 version makes some revisions to this.
     
  5. Alex9779

    Alex9779 Moderator
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    The Titan has a totally different mechanism for this.
    But the parts for the bowden extruder still are based on the same principles so there the issue might come up again.
    Fortunately it is easily fixed if you know what you have to take care of.
     
  6. Henry feldman

    Henry feldman Well-Known Member

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    Isn't the bowden a titan also?
     
  7. Alex9779

    Alex9779 Moderator
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    Nope, watch the parts.
    The bowden it is almost the same idler like now but a little extended to have a zone to push on with the finger.
    The tensioning is the same as now on the direct drive.
     
  8. Henry feldman

    Henry feldman Well-Known Member

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    Oh good, I love the tensioning on the current idler [note - dripping sarcasm] As evidenced by your post today...
     
  9. Alex9779

    Alex9779 Moderator
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    It is just a matter of understanding how it should work. Then it is easy what you have to watch out for.
    When building my box I though about and didn't get it, now that I ran into that problem and thought "hey why is that screw getting tighter and tighter and on the second extruder I can screw it and the square nut comes up?" I had a closer look and realised that the screw actually got a grip in the material what should not be...
     
  10. Steve W

    Steve W Member

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    Thank you, your excellent description has helped me get it right as I build. The nut was free to move up and down in the recess, but the screw was biting in to the plastic, I cleaned out the hole with a reamer and it now works very nicely
     
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