TPU Temperature Tower
I'm starting out with TPU and first thing's first, I ran a temp tower from 225 to 195 in 5 degree intervals (Bed temp of 40). As the temp decreases, underextrusion increases but bridging improves.
The perfect layer was the first at 225 but has no backbone when it comes to the bridging.
My question therefore is, is this the inherent nature of TPU (that is, no to minimal bridging) or do I need to dial it in more? Some additional details below:
- PRINTER: i3 clone (Mk8 extruder)
- Extrusion multiplier: 1.
- Material density selected: PETG
- Speed: 40mm/s
In general, the bridging with TPU will always be worse than with ordinary filaments. This is because the greater flexibility of TPU implies that it will be more saggy when printing in mid air. However, it is possible to adjust the bridging settings to improve the result.
For starters, try lowering the bridging extrusion multiplier. This is called "bridge flow ratio" in PrusaSlicer. In cura, you have to tick "enable bridge settings" under Experimental, then set bridge wall flow and bridge skin flow.
Setting a number lower than 1 will make the printer extrude less filament than strictly speaking required to bridge the given gap. The result is that the filament is pulled taut by the nozzle because it doesn't extrude as much.
Start with a value of 90%, and if that improves the appearance of the bridge, try 80% and keep going until you don't notice any improvements. It should initially improve as you go lower, then at some point it will get drastically worse as the filament will get pulled so tight that it breaks, thus failing to print the bridge.
Aside from extrusion multiplier, make sure your cooling override for bridges is set to use 100% fan during bridging. In PrusaSlicer this is under Filament Settings -> Cooling -> Bridges Fan speed. In Cura this is under experimental -> Enable Bridge Settings -> Bridge Fan Speed.
Let me know how it goes!
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