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Printing TPU (or other flexible filaments)

Posted by Bearded Flyer 
Printing TPU (or other flexible filaments)
August 10, 2023 10:19AM
Does anybody have any experience, and hints and tips, on printing with flexible filaments such as TPU?
I have searched the Mendel90 forum and have not found anything.

I want to make a flexible nose cone for a slope soaring model glider to absorb some of the impact stresses on a not so perfect landing. It would appear that the Mendel90 is capable of printing the material but I wondered how the Wades extruder would handle it, i have thought of removing the guide tube from between the spool and the extruder to stop any pulling of the filament, and whether retractions would need tweaking. I normally print exclusively in ABS and I was looking at using those settings in PrusaSlicer as a starting point.
Re: Printing TPU (or other flexible filaments)
August 11, 2023 10:38AM
I print TPU on my Huxley90 that has a direct drive extruder feeding a 1.75mm J-head hot end, see [hydraraptor.blogspot.com].

The path between the hobbed drive and the hot end is lined with a PTFE tube for printing TPU. I think that was the only mod I made. I print on glass heated to 95C for the first layer and off on subsequent layers. The hot end temperature I use is 230C and I print slowly at 20mm/s. My retraction distance is 3mm. The steps per mm is reduced compared to PLA because it rides lower in the hobbed drive.

Re: Printing TPU (or other flexible filaments)
August 12, 2023 06:19AM
Thanks for the info.
Is there any reason why you did not use one of your Mendel90 machines to print with TapU?
Re: Printing TPU (or other flexible filaments)
August 12, 2023 09:19AM
They all have 2.85mm hot ends and Wade's extruders, which have a longer filament path, and I haven't bought any 2.85mm TPU, although it does exist.

It might work with perhaps just the addition of a PTFE liner in the lower filament path.I think stiffness is the fourth power of diameter, so that probably compensates for the longer filament path.

I think for the best filament control a different hot end / extruder combination to keep the filament path as short as possible would be better. I get quite a lot of ooze and stringing, although recently I think drying the filament would be beneficial as I reprinted something with the same g-code and got much worse results from the same spool of TPU.

Re: Printing TPU (or other flexible filaments)
August 12, 2023 09:28AM
Another issue is because the printed part is flexible you can't print tall thin things as they start to bend away from the nozzle.

Re: Printing TPU (or other flexible filaments)
August 12, 2023 01:48PM
I did wonder how the Wades extruder could handle flexible filaments and you have confirmed my concerns that compression and stretching would be a major concern.
Thanks for the information. I think that I will stick to printing hard plastics with my Mendel90.
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