PTFE coupler - Theory and practical details

Discussions concerning the Ultimaker 2 / Ultimaker 2+ series of printers, including the Ultimaker 2 Go
reibuehl
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Re: PTFE coupler - Theory and practical details

Post by reibuehl »

Shouldn't it be sufficient to tighten the metal coupler with a defined torque if the spring replacement is used? Then we would need something that allows to apply that amount of torque.
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Re: PTFE coupler - Theory and practical details

Post by Anders Olsson »

Nicolinux wrote:Hi,
Thanks Neotko for the link to this post. I've had some fun with failed couplers lately and I'd like to add a bit to the theory. My last coupler died after only 10 hours of printing with PLA. ..
I would say step one is to switch to the TFM-PTFE.
In my opinion the glass filled PTFE is even worse than the original pure PTFE and korneel has done quite some testing of the TFM-PTFE with great results as you can read in his post.

Regarding the solid spacer, I still have some ideas of a dual extrusion setup that would need one of the heater blocks to be adjustable, so I have been reluctant to put a solid spacer there, even though the spring is problematic.

When reading about the solid spacers in this thread yesterday I just could not resist attempting to design a printable, adjustable spacer :)
It just felt like it should be possible and it would allow me to play with dual printing without the springs.

Mentioned it to Neotko in a PM and said I would post a picture here:
2016-03-02-6846.jpg
2016-03-01-6843.jpg
It is certainly still a beta version, this one particularly designed for the I2K, but it appears to have survived at least a few hours of printing :)
Last edited by Anders Olsson on March 1st, 2016, 7:09 pm, edited 1 time in total.
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Re: PTFE coupler - Theory and practical details

Post by Neotko »

That's quite brilliant anders, also allows the player to test the preassure without having to dissasemble. I'll wait for a printabe beta since my um2 chinaclone it's about to arrive.
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Re: PTFE coupler - Theory and practical details

Post by Neotko »

Btw ... Did you just say 'Dual' ?... ºoº!
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Re: PTFE coupler - Theory and practical details

Post by Anders Olsson »

We have had plans for a new dual concept for like a year at least, I haven't had time to do much though and had some lack of inspiration ever since the old forum died.
The inspiration is certainly back now with this new forum though :)
Some rumors suggest that others are ahead of me on this concept though, assuming it works at all, so you might see it made available from someone else.
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Re: PTFE coupler - Theory and practical details

Post by Neotko »

The only problem with dual it's that the only really advanced software to be able to do cool stuff it's s3d. And believe me, it's not plug/play. But when you get it you can do absolutely anything (well almost, there's 3-4 thinks that it would need to really be perfect, specially the possibility yo add variables and maths to the scripts).
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Re: PTFE coupler - Theory and practical details

Post by Iltacitoduca »

I wish to share my thought about the deformation of the spacer...
So, have you ever noticed the shape where the spacer get in contact with the hot side of the integrated nozzle?



This could be the reason why the spacer begin to deform after some time... so, we have the same pressure pushing the both parts together But in that point the same pressure is concentrated on a small Hot area... this will lead the deformation of the teflon spacer more rapidly that in other contact area

This is why you find the PTFE deformed always in the same point IMHO

A merely solution could be a little bigger part...


perhaps not a permanent solution but will lead longer time to have a deformation
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Re: PTFE coupler - Theory and practical details

Post by Neotko »

Well much time has pass since I wrote that. Latelly I finally understand how to really assemble the um2 with fixed spacer hotend, the TFM doesn't get much problems. Also I know from others that TFM coupler it's lasting a good 500-2000h print time, quite a lot imo.

But yea if you over-tight it, it deforms quite fast, I fixed 2 by, once assembled, inserting a 2mm drill bit from the bottom, to remove the expanded PTFE. It did work, well they have been printing quite a lot since that.
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Re: PTFE coupler - Theory and practical details

Post by Iltacitoduca »

Yes. but a fixed spacer does not compensate for thermal expansion like a spring do
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Re: PTFE coupler - Theory and practical details

Post by Izzy »

With the design of the head components there is very little expansion that will compress the spring/spacer.
As a check take a measurement with the nozzle at room temperature and then at print temperature and see what the difference is, I would also measure to the nozzle tip.

I don't have the coefficients of thermal expansion for both the stainless steel and the brass at hand to calculate the actual theoretical expansions, but from the design I would guesstimate that the majority of the expansion will be in -Z, i.e. the nozzle to bed distance reduces.
If I've got time I'm going to try and both measure and verify by calculation the expansions, but it's going to have to wait untill after my holiday.
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Re: PTFE coupler - Theory and practical details

Post by Iltacitoduca »

Hi Izzy,
yes, due to the dimensions of the parts, the linear variations are small and cannot be measured as you suggest...
but we can calculate ...
http://www.engineeringtoolbox.com/linea ... -d_95.html

Now, even if they are small, I do not think that should be underestimated in a good project / design...
May be considered after others, but if this forum is for 3D printers so why not try a good design solution instead of continuing to patch them?

Then each one is free to implement it or not
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Re: PTFE coupler - Theory and practical details

Post by Iltacitoduca »

Ok, my new Widia tool for the nozzle was in my hands Friday



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Re: PTFE coupler - Theory and practical details

Post by Anders Olsson »

Iltacitoduca wrote:I wish to share my thought about the deformation of the spacer...
So, have you ever noticed the shape where the spacer get in contact with the hot side of the integrated nozzle?



This could be the reason why the spacer begin to deform after some time... so, we have the same pressure pushing the both parts together But in that point the same pressure is concentrated on a small Hot area... this will lead the deformation of the teflon spacer more rapidly that in other contact area
Since it is a threaded part the top of the thread that seats against the PTFE can not be perfectly round (the thread has to start somewhere).
That said though, the chamfer that used to be on early Olsson-blocks was removed some time ago...
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Re: PTFE coupler - Theory and practical details

Post by Iltacitoduca »

Anders Olsson wrote:
Iltacitoduca wrote:I wish to share my thought about the deformation of the spacer...
So, have you ever noticed the shape where the spacer get in contact with the hot side of the integrated nozzle?



This could be the reason why the spacer begin to deform after some time... so, we have the same pressure pushing the both parts together But in that point the same pressure is concentrated on a small Hot area... this will lead the deformation of the teflon spacer more rapidly that in other contact area
Since it is a threaded part the top of the thread that seats against the PTFE can not be perfectly round (the thread has to start somewhere).
That said though, the chamfer that used to be on early Olsson-blocks was removed some time ago...
Hi Anders,
then you agree that the coupling of the two parts is at least simplistic... don't you?

having said that, what does it mean that there is now no more chamfering? in which chamfering refer ?? the hot-end in my photo is the original Ultimaker
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Re: PTFE coupler - Theory and practical details

Post by Anders Olsson »

Your block appears to have little to none chamfer. The early ones had an additional chamfer where the thread starts, which some said would have a negative effect on the lifetime of the spacer, so that chamfer was removed.

I think that with the TFM it works good enough for most users. The early spacers (particularly the glass filled ones) were another story, they could have extremely short lifetime with PLA under certain conditions.

If you increase the area of the PTFE you will also potentially get a proportionally larger lifting force if there is a leak between the PTFE and the block.
So i am not sure that you solve the problems by increasing the diameter of the spacer.

I would personally investigate other hight temperature materials, like the Duratron spacer made by "gudo", or having an interface material between the PTFE and the block to decrease the temperature of the PTFE, like the I2K-washer from 3DSolex.
The theory behind the I2K is that by lowering the temperature of the PTFE you get down into a zone where the PTFE is much more rigid and thereby less likely to deform.
I tried both these solutions and both works fine for what I do with the printer. An additional advantage is that you can go higher than 260C for printing high temperature materials like Polycarbonate.
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