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fuh

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Posts posted by fuh

  1. [...] if I leave the filament in the machine overnight then I get cracked segments in the bowden [...]

     

    Same here (though not with every PLA brand). Seems systematic, very strange. Does anyone have an explanation for it? Maybe fumes of lactic acid (depolymerized PLA)?

     

  2. Same problem here with PLA (white) from GermanRepRap.com .

     

    Update: I have a suspicion that it becomes (more) brittle while staying in the bowden tube for a longer time. No idea why. Now I unload the filament whenever I won't print for, say, one day, and I think it's better now.

    Maybe an idea for you, too.

     

  3. I found a very simple solution to reverse the bend:

    Flip the filament spool winding direction and guide the filament around a ring. Like this:

    reverse bend filament feed spreading ring

    Although the image shows a modified spool holder, I tested it with the original spool holder and I reached 10mm^3/s no problem. (PLA, 210°C, original feeder, 0.4mm nozzle)

    Get the ring here:

    https://www.youmagine.com/designs/spreading-ring-for-reverse-bend-filament-feed-for-ultimaker-2

     

  4. I noticed that the infill left not only a little ridge where it overlaps with the shell, but also little droplets now and then. First I thought this doesn't matter because it is inside the obect. But then I noticed that on the following layer, these droplets are sometimes dragged to the surface when the shell is plotted, and there they remain as bumps.

    I simply reduced the infill overlap (in the experts menu in Cura) from 15% to 8% and the bumps were gone.

    Maybe it's helpful to someone.

     

    • Like 1
  5. I put a larger ID tube [...] making it a lot easier to print with slightly oversize filaments.

     

    And I remember a case (with an UM orig.) where the filament was completely stuck, it could even almost no more be pulled out by hand. All because the printing speed had been set far too high whereby the feeder had caused a lot of deformation and abrasion. Thus the friction was extremely high.

    I stay with my theory that friction forces after the feeder are the central problem, and those before the feeder are neglectable, compared. Why: The brake effect of pressing material through the nozzle must be by far higher than the brake effect of spool unwinding, and these brake forces are the cause for the friction forces. Just normal engineering logic.

    How much is the deformation by the knurled wheel, anyway? Could it happen that it increases the maximum filament diameter to more than the tube inner diameter? Then the friction would increase overproportionally. If the increased counterforce of the feeder wheel in turn causes deeper filament deformations (just a possibility, not an observation) then we have an escalating problem!

     

  6. I noticed that the filament scars make an approximate quarter twist in the bowden hose, so they move to the outside of the bend. This is pretty obvious because the filament wants to keep its bend and adapts to the hose bend.

    So I put the spool on the other side of the feeder, outside the printer, in order to have the scars on the bend inside. The quarter twist would reverse its direction. But I had to help it a little to do so because the last decimeters of the filament had already a screw shape in the wrong direction. So I deformed the filament end, using hot water, from left-hand thread to right-hand thread, before inserting it.

    The result confirms my initial assumption. Here it is:

    result of reduced friction test

     

  7. As far as I remember from university lessons long ago, friction is, astonishingly, only dependent on the materials of the objects that have contact and the accumulated bend angle, but not on the contact area amount. So my idea was actually not supported by that theory, but I think it does not consider possible elastic deformation of the tube walls (by the filament surface scars in this case). I could imagine that the friction will be increased thereby. But my intuition may be wrong....

     

  8. Test it yourself:

    Let transporting your machine a long piece filament. Use "Move material" to get it, and cut off a piece. Then push this piece in different ways in a curved Teflon hose. Various Teflon hoses are available on eBay. Or use the Bowden from your printer.

     

    I would expect that it's also much dependent on whether the bend orientation of the filament matches the bend orientation of the tube. But I don't know how to separate the two effects. Straighten the filament somehow maybe?

     

  9. Yes, obviously both work on the same principle. You could say, I'm misusing support as raft.

    Hmm, trying to remember why I thought it would be better than a raft... I think a thin raft can absorb much less contraction than a support structure. And it is my experience that a raft is hard to remove, but maybe that has changed? For parts without a flat bottom there is no transition from raft to support. I found an almost flat bottom is not easy to print without my trick. Or is it? But support generation strategies change all the time, and my experiences become worthless, I need to keep experimenting.

    So I could imagine an integrated support/raft structure with adjustable minimum height could be best.

    All this is just meant to be brainstorming.

     

  10. I managed to print some critical shapes by letting them "hover". That is, not letting them touch the platform level anywhere but having support structure under the whole part. That way, the support structure elasticity is used to absorb the tiny shrinkage movements that would else lift the corners or edges, sometimes invisibly at first but causing a bend that would escalate in the next couple of layers. So I may still get some slight distortion but it will not substantially bend a layer, and thus not escalate. For example I have applied this to nylon material which has severe warping problems else.

    In order to not let the part be automatically adjusted by the slicing program to begin at z = 0, I use to place some additional, tiny "dummy part" a bit below the needed part in my design.

    Maybe a nice feature candidate for Cura that a model can be shifted interactively in z direction, too, to achieve the same effect?

     

     

  11. I tried to print a pretty much "precision part" with ultimaker.com's black PLA. So I sliced with 0.1 mm and printed with just 25mm/s – but failed! This material, though molten, seems to be much less fluid than others, for example the light blue one, at the same temperature. The effect was that it seemed to disintegrate to droplets when it left the extruder, resulting in an ugly, "torn" structure. I aborted the print job. Then the idea came to my mind that there might be some kind of minimum flow, so I tried again with 0.2 mm and 50 mm/s. The problem is gone, the result looks perfecty even!

    My conclusion: Fine slicing or slow speed doesn't guarantee a better result!

     

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