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chrili_rakete

Yet another Bowden Fix!

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Dear all,

may I suggest another fix for the annoying hot-end-issues with the bowden tube. I think my proposal is a very simple solution that can be realized within 10 minutes - no printed parts are necessary. Although I have no long time experience I expect the tube to be connected reliable in that way. The idea of tapping a thread into the tube is based on a discussion here: https://groups.google.com/d/topic/ultimaker/zcFB28_FCa0/discussion - thanks to everyone who contributed!

You will need no extra parts, but the following tools:

- M5 and M6 taps

- an 8mm drill or a M8 tap

- a plier

These are the necessary steps:

1. Disassemble the hot end.

2. Fix the print-head-sided end of the Bowden tube with a plier and tap a M5 thread of about 6 mm length into it (this is just to maker the next step easier).

3. Now do the same as in step 2, but with a M6 tap. You should now be able to turn the M6 brass pipe into the thread of the tube. Try it, but take it apart again.

4. Fix the PEEK insulator with a plier or a vice. Widen up the hole on the upper, non threaded side to a diameter of 8 mm by using a drill (I used a M8 tap instead). Do this to a depth of ca. 10 mm, but take care that you don't drill through the hole part! Check and retap the remaining M6 thread on the other side of the PEEK insulator afterwards.

5. Assemble the print-head, turn the Bowden tube into the thread of the brass pipe.

Voilà: the Bowden tube should be connected tight to the brass pipe now - and you also have got presents for the next two birthdays of your mother-in-law: a white push-in fitting and a blue plastic horseshoe!

Hope this helps, thanks for testing!

--

Christoph

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I am not sure if that is such a good idea:

1. the bowden tube (PFA or PTFE) has a working limit of 250C. in the original setup, or with Taylors M7 threaded bowden, the bowden has only a small point of contact with the brass, and hence doesn't get hot over the working limit.

2. connecting the bowden for 6mm directly to the brass can heat it near to, or even above the working limit, weakening the M6 threads you carefully put in (the walls of the bowden tube become severely thinner in this process), and the connection will most likely disintegrate, sooner or later.

3. you limit how much brass/peek connection you have, further weakening the mechanical stability of the system, to a point where even the threads of the peek can rip out. (peek has a limit of 300C, but if only 3 turns of threading holding the brass, it'll break sooner)

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Dear Joergen,

thanks for your reply, I can understand your concerns. Weakening the structure of the PFA tube by the heat inducted directly by a part of the copper tube is an issue that has to be considered. As you have already mentioned, the maximum working temperature of PFA is about 250-260° C (the melting point is about 305°) - that is below the maximum extruding temperatures I use. Apart from that I suspect the temperatures at the connected upper part of the copper tube to be always lower than in the nozzle area. Due to the direct connection of the copper and the PFA tube (what I see "per se" as a conceptual advantage of this design) I don't expect very heavy forces on the PFA tube from uplifting melted plastic, so even a structural weakened thread (by high temperature) should not fail. What could be done to improve the stability of the thread is to reduce the size of the drilled hole from 8 mm to the exact outer diameter of the PFA tube turned on the copper tube, ca. 7,5 mm, to give it a tight fit.

Refering to your concerns of breaking the PEEK insulator by reducing the length of the M6 thread I just can tell that this still makes a very stable impression on me.

Last but not least, let me explain my very pragmatic approach: I had a brandnew Ultimaker that did not work due to the known Bowden tube hot-end issues. I invested hours and hours and tried every workaround I found - without any sucess. I am sure that Taylors part would solve the problem, so I put my name on the list. But I don't know if or when I will receive it ...

Now I can use my Ultimaker without any problems. I did not have to invest a lot of time or money to realize this fix, and the only thing I risk is that the PFA tube will slip out again or the PEEK insulator might break earlier. So for me these are very good reasons to continue working with and testing this fix.

--

Christoph

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You are right, many of us had the same issue with the bowden popping... from my experience, I just think that your solution will add more problems than it is solving. PFA and PTFE may be rated up to 250C, and may melt at 300C, but both loose a significant amount of mechanical stability getting close to the max working temp.

here is an example of a PTFE hot end that failed:

IMG_5407%2520PTFE%2520hotend%2520failure.jpg

it was perfectly fine for ABS up to 235C... changing the temp to 240C destroyed the PTFE hot end immediately, and the whole brass tube got pushed down. and this was a substantially thicker part of PTFE than the whisper-thin tube of PFA you are proposing.

As I said, it might be good for a while, but my guess is that the threads inside the PFA bowden will fail, and the filament pressure will simply pop the bowden, and in my opinion rather sooner than later, since it is hot around the brass tube.

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You are right, many of us had the same issue with the bowden popping... from my experience, I just think that your solution will add more problems than it is solving.

So apart from the tube slipping out, a breaking of the PEEK insulator and completely messing the nozzle: what is your expected worst case scenario of problems?

Thanks for the picture, but I see that this might be a slight different situation concerning heat and forces on your (broken) PTFE part, as it is directly contacting the heater with its full surface. These pictures illustrate the situation here, and maybe you can understand why I do expect significant cooldown-effects in the threaded contact area between copper and PFA, due to the functionality of the remaining part of the PEEK insulator, the longer distance to the heater and the intrusion of new "cold" filament at this point.

Img3370.thumb.jpg.41094e20818f5a1bdaeb38a66fd96d19.jpg

Img3374.thumb.jpg.7c7ec18aa0c20cd0bf98d2a3c5801f27.jpg

There is no discussion about the proposed fix means a weakening of the structure, but if this still will remain stable enough. For me this tradeoff makes a perfect deal, as the solution is available easily and immediately and - until now - it just works very fine! Of course I don't know for how long it will last, but I think the answer to this question will rather be given by an empirical than by a theoretical approach ...

Every fix or workaround I know has more or less a weak point, and the one of Taylor's part is obvious: I just don't have it here now ...

P.S.: Half an hour ago I put the hot end with a piece of tapped PFA on it into my kitchen oven with a temperature of 250°C (I am not equipped to measure this, but it seemed to be quite hot), showing no relevant signs of weakening the thread. Using reasonable force, I am not able to tear the PFA apart from the copper with two pliers.

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As I have said, it may look great in the beginning, it may be good for printing PLA temps for quite some time. I just wanted to point out that is can fail fast&hard once you reach a certain temp threshold. also, the filament pushing into the head exerts a pretty big force, while it's hot, and your plier test in the kitchen oven already dropped the temp way under the threshold, so of course it felt OK.

As I said, if you like the solution, go for it. I just wanted to be sure that other with the same problem know the problems involved, and don't get expectations that are too high.

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I think it is very simple. This solution by now has been tested for quite some time, so there doesn't seem to me a reason to further challenge it. As they say, the proof of the pudding is in the eating. Can you tell me how long this fix has been stable now?

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