I’m new to printing TPU, I’m printing it on my Power Spec i3 Duplicator Plus (rebranded Wanda) it a direct drive. This is a bumper for an RC car, I printed on using the same brand TPU but a different color also less infill. I need to go through the gcode and see if the settings are the same other than the infill. I’m printing at 30 or less. My thought is that it has to do with the infill which was gyroid at 90%. I’m going to double check the speed setting and change the infill to 100% and see what happens.
I have a spool of TPU but haven’t opened it yet. That’s an interesting stringing tower 
Strange that it starts out fine then goes to pieces. It looks like it’s over-extruding as it goes on.
Have you looked to see if there’s leakage from the hot end? I’ve had that cause effects like this. It will be obvious once the silicone boot is off if that’s the cause.
@Gramps I have a couple of questions. Is the fan still running and what temp are you printing at. Have you done a post processing and forgot to remove from a previous print?
The fan is running at 100%, Overture TPU Space Gray 200c there was no post processing done, that was the 1st print of the day. The odd thing is that the piece printed just fine using Overture Gray TPU filament, but for what ever reason I turned it 45 degrees on the bed. So I tried that and it was better but still not right. The picture is the Space Gray turned 45 degrees. Can’t say for sure if I had the fan on or off when I printed the light gray.
The problem is the flex of the object. The taller the print the more flex is in the tower and the more complex the infill is, the more movement happens.
In simple words. The nozzle is bending the tower while printing. If you have a little over extruding the bending accelerates.
I printed a lot of objects vertically in TPU and while printing the top you can see the tower bending several millimeter in all directions. You can see that your towers are fine, until there is enough material below the print area, so the towers start flexing while the nozzle is applying more TPU. Cooling and temperature won´t help here. There is no switch to disable flexing while printing.
Especially with a square shape the movement is limited to x/y. My prints where circular and the tip of the tower was circling softly while printing. Since a circle tower is a slow continuously movement in all directions, I assume with your small diameter and the sharp corners the tower releases the bend instantly, which causes the nozzle scraping the filament to the outside, which results in the bulky result.
Summery: Thin vertical TPU prints are possible, but it requires luck and a proper shape to succeed. In your case I would print the model flat. Yes, you will need support and yes cutting TPU support is a pain in the ass, but the flexing will ruin your prints. Especially with a small tower diameter. The bigger a print is the less flex/bend the TPU tower will have while printing.
@Geit I believe your right about the vibration on the towers. When I first printed it in gray as that was all I had at the time I could see the towers moving, that was printed at 30% infill probably gyroid. The darker gray was printed with 100% infill. When I get finished printing on my Ender 3 v2 I want to set the TPU printer back up and use the same gcode on the dark gray just to see what happens. I ended uo laying it down and dealing with the supports.
All I have printed with to date is PLA though I have a full roll of TPU and PETG that I have been sitting on for a special project (whatever that might be). That is a good warning about TPU.
I have been loath to open them up because people say they are hygroscopic and until I had a proper use for them I didn’t want to have that added hassle.
I’m not sure PETG is more hygroscopic than PLA.
You would certainly know better than I. I just heard that somewhere so I keep them closed till I have more to print. It would be interesting to try them out on my model T Ender.
I keep all my filament in a sealed container, not really air tight. Besides the filament I also throw the desiccant that comes with the filament in the box too. I also keep one of these in the box Amazon.com
You mean I should quit storing my filament in the shower? Just kidding. Winter in Montreal is not when it is humid so I don’t worry much about it now.