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Torgeir

The Setup of "Bowden Tube" and filaments orientation in the tube.

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Hi Folks,

 

This topics almost went into the drain, -but actually this is a very important issue for an "FDM Bowden type" printer.

When I had to tag this topics, I did not find the "tag" I was looking for, -so I just put up the "one" I have. But the fact is that, this is valid for every Bowden tube printers that's made.

 

So you may ask, what is the issue; -the issue is friction!       So, I'll say, friction is the Achilles heel of "FDM Bowden type" 3D printers.

Friction in the transfer line some place; -"between the the bowden tube and the filament"! 

 

How to fix this? 

1)  Can we reduce the friction(?): Yes or No.   

2)  Can we increase the feeder torque(?): Yes or No.

 

If you'd ask me in the beginning of my 3D printing "period", I would say no to the first question and yes to the second question.

 

But today, I'll say yes to both questions! 

I'we put much effort into this problem, cause there was never any good answer to this issue, but now I understand the strange feeding we sometimes being observed during first layer and elsewhere during printing.

 

Actually, I'd feels like walking around the bushes in this issue, but not anymore..

 

If this interest you, read on. I'll focus a little about the general things first.

 

I’ll like to focus a little on the bowden tube and how it should be set up on this kind of printers. This might look strange for some, but may help others..

The bowden tube work best when it can stay with looping upward during printing, without tilting much to one or the other side. In order to keep this loop as perfect as possible, I’ve installed a tiny carbon fiber rod (max diameter 1 mm). This carbon rod is to be strapped to the wire bundle and only one attachment to the bowden tube at the very top of the loop.

Like this:

How the straps is arranged.

Top_Strap_Bowden_Tube_1.thumb.jpg.8ffc904659e0bc9a8cdac0c8af580310.jpg

 

Here you see the one place they are "attached" together. This is needed as both (Bowden and Wiring) are attached offset from each other at the extruder and at the feeder, now they can move freely without interfering each other. 

Top_Strap_Bowden_Tube_2.thumb.jpg.ae04118e5117e2a3788cc7afb7f86c27.jpg

 

 

On the printer:

Bowden_Loop_Top_Strap.thumb.jpg.14e4fd8244ed4a16d6f0c2211a3b0dbc.jpg

 And with a top hat special..

 

This rod should be solid strapped to one of the four screws that’s holding the extruder attached together. When referring to parts in the printer I’ll always refer to looking strait into the printer, -so the long screw to use for the carbon rod and the wiring wiring loom (or cable), will be the aft. R/H screw to strap into. This carbon rod also need to be strapped alongside the feeder unit together with the wiring loom.

How to strap up the wire loom and the carbon rod from the feeder and toward the extruder is also an important detail to include in the whole setup. This strapping when done right, will prevent the wiring to be bend all the time in the same area when extruder move around, such thing is awaiting a rupture here (–an open wire) causing a malfunction in your printer to come. Also important to note is this; there should be NO connector located inside this wiring loom!

 

Now to the question why do such a setup improve our printer? In order to explain this simply, just cut two peaces each about 1 meter from a roll of filament with a light color, white will be the best choose, if you have. Now you should have two equally curved up filament lengths, right? Find a black filth pen, the permanent type (no withe board pen, we don’t want remains from this into our bowden tube).

No mark the outside of the loop in the whole length with a black visible line on one of this filament and make a black visible line inside the loop on the other piece of filament. Now, let it dry..

 

OK. As the “ink” is dried, we can make a little test. You do not need to power up the printer, but if you have an old UM2 you need to power up and just feed the filament to the extruder and stop here, do not turn the heater on (no need). For those with the +model, just feed, with the press wheel retracted, all the way to the extruder. Make sure you feed this piece of filament in the same attitude, as it is delivered from the roll of filament normally attached to the printer.

 

Curved_test_Filaments.thumb.jpg.f2efb02c4fad2e660133da05b61495c7.jpg

 

Here is the two test filament, pre cutted deg. and ready to be inserted into the printers bowden tube.

Make sure that the extruder is parked in the normal rest position, in the forward R/H position.

Now you can choose any of the piece of the two test filaments you have, just feed it into the bowden tube as described above until it is at the extruder.

 

Now look at where the black line is located when looking at the bowden tube, it should be possible to see this line. So, if you choose the one with the black line outside the loop, you will see the line following the upper side of the bowden tube. Right?

And of course, vice versa, when feeding the other filament into the printer.

So, as the filament extend into the bowden tube, the “arm” will extend while filament gradually change direction and this will increase the torque that’s will twist the filament starting at the feeder. So sure, this “twist” torque will variate as the extruder move around on the heath bed.

So what is the point of mention all this, well, we can very much benefit from this “facts” -armed with this information.

 

The key word here is friction. In order to keep the friction as lo as possible, we would like to have the filament as clean as possible when it is forced toward the upper part of the (Teflon) bowden tube. All this is to prevent additional “drag” for our feeder system in order to be as efficient as possible.

If we can achieve this, we do not need this “very strong” feeders, that can create a force up (10-14.. and some more!!) KP., -a pressure “normal” retraction cant cope with..

 

Now lets have a quick look at the system:

 

This is something from many months ago, however, an important note here is; If the friction constant is 1, we would not be able to move the filament inside the bowden tube at all. If it is zero there will be no resistance when moving the filament. Sure this is just the extreme extends (theory), a friction constant will always be some place between (0 and 1).

 

Bowden_Outer_loop.thumb.jpg.4b4ded897d3b1f5a51c557991eec1ea4.jpg

 

According to this drawing, it is oblivious that outer “signature” track wheel cause increased wear inside the upper part of the Teflon bowden tube. Knurled wheel much less than hubbed wheel, so hubbed wheel should absulutely not be used on the outer side of the filament to drive the filament through the bowden tube! This because the hubbed wheel makes crossed cut along the whole filament length and really scrape into the Teflon. It is just a matter of time before it will fail, if it is installed grabbing the outer side of the curved filament. For the knurled wheel, this work better, but will in time also suffer for this kind of wear and tear. This occur when the system using knurled wheel have to produce higher pressure, the small pyramided dig up a nub behind every hole it makes and those small nubs work as small grinders to the Teflon surface. The Teflon surface is kind of soft and is easy to rub down.

Printing this way is not very efficient as it create other problems due to the higher working pressure. The other feeding way, feeding in the inside loop, do not need high pressure, due to lo friction -and is much more easy to control..

 

Now to the worst problem here; when the bowden tube is “rubbed up”, due to this above issues, -you do remember the twisting of the filament during extruder normal movement. Well, -due to this twisting when the head move around, the friction factor might/will variate and so will the extruder pressure as well.

I’ll guess you know very well how the rest of the story will end.

 

Bowden_Inner_loop_2.thumb.jpg.ceb587ce75a3bd4a9b04953e809d8c54.jpg

 

 

Well folks, this one is not very easy to realize, but really is an improvement.

 

Thanks.

 

And thank you @gr5 for fixing up my mess.. :)

 

Torgeir. 

 

 

 

 

 

 

 

 

  • Like 3

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The top hat was the simple way to extract filament fume out from my experimental room. So I had this plan, but before I could do this myself, my son fixed all this cause his mom did not like the fume from the PLA..

There is a fan that can be speed controlled and the big housing go to outside vent.

 

So easy..

 

Torgeir. 

 

Edited by Torgeir
Wording.

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Is the Bowden tube PTFE on the ultimakers?

Shouldn't really show wear from unfilled filaments then.

If it isn't that's an easy way to reduce friction even more.

 

I have PTFE liner in one of my welders and there has been many meters of steel and aluminum wire going thru that one over the years without visible wear.

The wire feeder is in principle the same as a Bowden.

 

Well written article 

Edited by AndersK
  • Like 1

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On 8/31/2018 at 2:29 PM, chuck-yanke said:

Torgier

I love the article! Can you take a pic of how you attached at both ends? Did you get carbon rod on Amazon?

 

Hi @chuck-yanke,

 

Thanks, here is details in pictures. 

Try a local model aircraft shop, they should have carbon rods approx (1 mm X 1000 mm) thats give you some extras for attachment.

 

Good luck.

 

Thanks regards

 

Torgeir.

 

Extruder_Carbon_Rod_Detail_1.jpg

Extruder_Carbon_Rod_Detail_2.jpg

Extruder_Carbon_Rod_Detail_3.jpg

Extruder_Carbon_Rod_Detail_4.jpg

Edited by Torgeir
All text dissapered... :( This is not very good...

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