TwoTrees SK1 extruder cover

For TwoTrees SK1 a modified extruder cover to avoid TPU jamming.

Also the spring is too long, cut 2mm or change with a new one 6 mm outher diameter, 10 mm long and 0.7 mm wire diameter or 0.6 for softer feedback (needs to be screewed more for harder filaments).

Edit: available also a slotted version to help gear overheating.
But this problem is mitigated changing run_current value. 
Normally a small extruder motor runs between 0.35-1.0 Amp. Try values between 0.65-0.80 and check also extruder's skipping.

[tmc2209 extruder]
uart_pin:MKS_THR:gpio6#PC11
run_current: 0.8 # 1.0 as stock seems a bit high
#hold_current: 0.5
sense_resistor: 0.110
stealthchop_threshold: 0
interpolate: false

 Print in PETG/ASA/ABS/PC/PA.