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I recently obtained some PTFE tubing to replace the PFA on my bowden tube and I must say the filament slides much better down the PTFE tube than the PFA, and it doesnt seem to me (at least just from handling the tube) that its any weaker... The thingiverse bowden clamps (

http://www.thingiverse.com/thing:17027

) hold the PTFE tube QUITE well, so I can't seem to figure out what the problem is; why didn't UM use a PTFE tube to start with?

Does anyone know their precise reasoning? Are there subtle problems I am not aware of?

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I recently obtained some PTFE tubing to replace the PFA on my bowden tube and I must say the filament slides much better down the PTFE tube than the PFA, and it doesnt seem to me (at least just from handling the tube) that its any weaker... The thingiverse bowden clamps (

http://www.thingiverse.com/thing:17027

) hold the PTFE tube QUITE well, so I can't seem to figure out what the problem is; why didn't UM use a PTFE tube to start with?

Does anyone know their precise reasoning? Are there subtle problems I am not aware of?

I think they used PTFE in the beginning, and then switched to PFA (for to me unknown reasons). I got replacement PTFE, and I didn't thought there would be any significant difference... maybe PFA is a bit stiffer, and causes less "bounce" in the bowden when the filament retracts. but to me it's all the same.

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PFA is generally used for plastic lab equipment because of its extreme resistance to chemical attack, optical transparency, and overall flexibility. PFA is also used often as tubing for handling critical or highly corrosive processes. Other applications for PFA are as sheet linings for chemical equipment. Because of its properties, it can facilitate the use of carbon steel fiber reinforced plastics (FRPs) as replacements for more expensive alloys and metals.

Polytetrafluoroethylene (PTFE), on the other hand, is also a synthetic fluoropolymer of tetrafluoroethylene. DuPont Co. is the most well-known producer of PTFE which, as mentioned before, is the material most people know as Teflon. Building from the accidental discovery of Roy Plunkett, PTFE is a high-molecular-weight compound comprised of carbon and fluorine. Essentially, it is a fluorocarbon solid. It is hydrophobic, meaning water or substances containing water can get it wet due to the fluorocarbon’s characteristic of having mitigated London dispersion forces. Thus, PTFE possesses a very low coefficient of friction when in contact with solids. This is because of the high electronegativity of fluorine. Other than Teflon, PTFE is also commonly called Fluon and Syncolon.

source

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Thanks wikipedia... I wanted to switch to PTFE because of precisely those low-friction properties. Yes PTFE gets soft when it heats up BUT I have a fan cooling the top of the PEEK insulator and that big heatsink is there so it shouldn't be heating up anyway. How much do we care about chemical inertness? We are not pumping acid through. The question is: is the force of extrusion enough to bend the PTFE tube out of shape? I think the drive gear would strip before that happened...

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Thanks wikipedia... I wanted to switch to PTFE because of precisely those low-friction properties. Yes PTFE gets soft when it heats up BUT I have a fan cooling the top of the PEEK insulator and that big heatsink is there so it shouldn't be heating up anyway. How much do we care about chemical inertness? We are not pumping acid through. The question is: is the force of extrusion enough to bend the PTFE tube out of shape? I think the drive gear would strip before that happened...

I have PTFE bowden, and nothing is bent out of shape. perfectly fine.

btw, I found this handy chart:

http://www.plasticsintl.com/sortable_ma ... flection66

it looks like PFA gets softer at a much earlier temp than PTFE (75C vs 140C)

and now a wild hypothesis: does PFA bowden cause more hot end "clogging" because it gets soft, deforms inside the PEEK well (the downward force from the 4 screws is bigger than the "pressure" upwards from the filament), and restricts the filament flow?

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Just as an update, I installed a PTFE bowden tube in my ultimaker like a month ago and have been printing ever since. No issues with stretching, popping, etc. In fact I just switched out the silver PLA for blue and all I needed to change was the filament diameter in KISSlicer. Everything else just worked, and I feel like part of that is due to how much slipperier the tube is.

EDIT: I did have to replace my bowden clamps with these

http://www.thingiverse.com/thing:11864

http://www.thingiverse.com/thing:17027

EDIT2: Well maybe I didn't have to... but I did.

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I think they used PTFE in the beginning, and then switched to PFA (for to me unknown reasons).

I raised this question, and nobody seems to know for sure. However, I they gave me an early tube to compare to the new tube. I cannot see any difference.

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PTFE won't help much, to the point of gaining extruder force. But using an extruder setup like @ultiarjan did with his might.

https://www.youmagine.com/designs/feeder-for-ultimaker-2-rail-system

This will raise the feeder, cutting down the curvature of the bowden, allowing a more natural (less curves, less constrain) along the tube. Also the feeder is a @IRobertI version, so it will work better than the UM2 one.

Ofc, you could also just buy a better feeder to Bondtech, or go through the weird part of buying all the um2+ feeder parts one by one and assembling it, since UM distributors don't sell the um2+ feeder assembled...

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