SEND HELP!! I desperately need help with TPU printing!!

[curious aardvark]

okay - first: what printer are you using ?
Ah okay creator pro.

First thing - have you done the extruder mod with little bits of ptfe ?

Secondly - give up on ninjaflex. It's just too soft to be of much use.

what you want is a cheaper tpu that is a little stiffer.
https://www.amazon.co.uk/gp/product/...?ie=UTF8&psc=1

I've used all four colours of this stuff and it gives really clean prints.
Printed at under 0.5mm thicjness it's super floppy and totoally unbreakable.
The blue is the most flexible and the red the stiggest. Minor differences - but you do have to print the blue slower than the red.

My simplify 3d rep pro settings
I don't actually use simnplify 3d for the rep pro clone. I use flashprint.
It's just so much easier to use for the dual extrusion and apart for lacking a z-offset setting, just as easy to use and well laid out as s3d.
https://www.flashforge.com/download-center

My current flexible tpu profile for flashprint attached.

But it's not the slicer settings that are causing you grief - it's just that ninjaflex is hands down the worst tpu out there at the moment. All the cheaper stuff is better - and a lot cheaper :-)

Oh and set bed temp to 0c.
tpu does not need a heated bed and will stick to anything and everything like glue with no heating.

print temp 235c - ignore what it says on the reel - it's pretty much always wrong.

max print speed 30mm/s
retraction setting as short as you can get - 0.8-2mm.
retraction speed - 40-50mm/s - start on the slower setting.
travel speed - slightly faster than print speed. I use 30mm print and 40mm/s travel speed.

The good thing about tpu is that you can set EVERUTHING to 100% of print speed.
This cuts down on print time.

I generally use 0.2-0.3 layer height.
tends to give cleaner results than 0.1.
0.16 is about a slow as I go on tpu.

I'm doing alot of tpu printing at the moment. and my default bombproof settings are (NOT for the rep pro).
0.25 layer height, 30mm/s print speed. 2mm retraction, 235 print temp and ambient temp for bed (0c).
Everything set to 100% of print speed.

It's interesting that the sapphire pro2 gives a much cleaner print with tpu than the rep pro clone (knp-klick-n-print).
The distance between the extruder and the hot end is 105mm on the sapphire and about 30mm on the knp.
The general mechanics on the sapphire are just a lot better and it really does get reflected in the actual prints.

But as far as stringing goes - just dump the ninjaflex - I've had a roll of the damn stuff in my workshop since it was invented and I have never been able to get a half decent print from it.

flaxible pla used to be my goto flexible filament. These days it's the current generation of tpu.
Just great to print with and zero stringing.