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Ultimaker^2 Reduce filament friction in the bowden tube?

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It seems that inside the tube, the rough side of the filament (caused by the knurled wheel) runs always along the outside of the bend. What do you think, does this increase friction because the main forces are on that side? I'm not sure.

But if so, could we then reduce friction by turning the feeder on its back side (it seems symmetrical) and invert the feeder motor direction? Then the rough side should run along the inside.

Or, would it be sufficient to mount the spool holder somehow on the other side of the feeder (that is, outside the printer)?

 

 

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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?

 

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The sum of all (possible) small brake factors, make of it at the end, a very big thing. Therefore, it does not hurt to look at each component of the material transport system in more detail.

Even a guess on my part:

I think the Bowden should be close to the filament as possible, offer little room to develop. Otherwise, it extends the retraction path. :rolleyes:

Another thought:

The traces of the knurling wheel change the filament surface, it creates small spaces, thereby the friction could reduce rather something. :rolleyes:

Markus

 

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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....

 

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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

 

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I think having the spool *lower* is more important than having it on the other side. This allows the filament to enter the feeder more vertically instead of at a steep (45 degree?) angle so there is much less rubbing on the entrance to the feeder.

A good second test would be to keep the spool at the same height but on the other side.

 

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I think having the spool *lower* is more important than having it on the other side. This allows the filament to enter the feeder more vertically instead of at a steep (45 degree?) angle so there is much less rubbing on the entrance to the feeder.

A good second test would be to keep the spool at the same height but on the other side.

 

Your theory, your turn. ;-)

 

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Skint, the Bowden tube is important because it is what ensure that the amount of filament fed in at the back of the printer is the same amount that arrives at the hot end, and gets extruded. Without a confined path for the filament, when the extruder turned the filament would just flex and extend, and not get pushed out of the hot end in exactly the same amount that the extruder advanced.

That said, I think it would be interesting to see what difference a larger ID makes. I put a larger ID tube on my Ultimaker Original (0.15" - about 3.81mm iirc) and didn't really have major problems, while making it a lot easier to print with slightly oversize filaments.

While it would increase the needed amount of retraction slightly, that might be compensated for by simply increasing the retraction speed. One of the supposed advantages of the non-geared extruder design was that it was supposed to be able to do retractions faster. But in fact we still run it at the same speed or slower than the Ultimaker Original retraction. Definitely worth experimenting with, I think.

 

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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!

 

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Illuminarti, fuh

Thanks for the info. I was assuming that with such a long length of Bowden, any compression within the filament will only be exacerbated, in theory creating more friction and possibly stringiness. I assume Bowden`s are made from PTFE? If I could get hold of a slightly larger I/D Bowden I would trial this for a while, as I would be interested if this makes any difference at all.

I understand that keeping the material feeder away from the hotend allows for greater accuracy and quicker printing speeds.

 

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It seems that inside the tube, the rough side of the filament (caused by the knurled wheel) runs always along the outside of the bend. What do you think, does this increase friction because the main forces are on that side? I'm not sure.

But if so, could we then reduce friction by turning the feeder on its back side (it seems symmetrical) and invert the feeder motor direction? Then the rough side should run along the inside.

Or, would it be sufficient to mount the spool holder somehow on the other side of the feeder (that is, outside the printer)?

 

I chose the latter option:

left rear

 

Now the rough side stays on the inner side of the Bowden tube. Before I made the hack, I used to have the filament spool on a lazy Susan on the floor. However, in my room it was a very unpractical location - not least because of my two-year-old son who got very interested in the filament (and the lazy Susan made of glass). IMHO the current location is better also in terms of ergonomics, but that of course depends on preferences and environment.

 

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Is your printer on a turntable!!?? If so that's very cool!

 

Thank you! Yes, I have liked the setup myself. Earlier on I had to get behind the printer to reach the feeder and the filament spool was on the floor - ergonomics and level of compactness were terrible and I decided to optimize them a bit. I used this kind of a swivel between two wooden plates:

http://www.amazon.co.uk/Shepherd-Hardware-212482-Lazy-Susan/dp/B000HJ70WK/

http://www.amazon.co.uk/Web-Traders-Online-BEARING-TURNTABLE/dp/B00AFUKMOY

There's also a simple mechanism (printed with my UM2 :) to snap the turntable to its default orientation.

 

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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

 

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