This is a volume pedal for electric guitar. It has been designed to be very strong for a 3D printed pedal and the belted mechanism is consistent and reliable.
It also has mounting holes in the back so you can add a 3 pin 6.5mm jack for it to be used as an expression pedal, and there is a hole for a switch so you can switch between the 2 modes.

You will need:
A short length of GT2 6mm wide belt.
A 16 Tooth 6mm wide GT2 pulley with a 6mm bore.
2x 6.5mm mono jacks.
Wire
1 or 2 springs - 1" long, 5mm diameter.
2x M6 lock nuts
2x 25mm M6 Bolts
13x M3 lock nuts
12x 10mm M3 Bolts
5x 30mm M3 Bolts
4x Smooth 20 Tooth sized 6mm wide 3mm bore GT2 idlers.
Aluminium foil for shielding.
A potentiometer - Although any 250K/500K pot will work, I recomend using a Dunlop super pot because they are high quality. https://www.jimdunlop.com/super-pot-250k-solid-shaft-potentiometer/
Cheaper pots can be unreliable.

Optional for expression pedal mode:
A stereo 6.5mm jack
DPDT toggle switch

The springs are used to tension a lever which keeps the belt tight for the whole travel of the pedal. I used 1 spring, but there is provision for 2 springs if you use weaker springs.

Custom

No

No

20%

The more wall thickness the better, but I used 3 walls with a 0.6mm nozzle and 4 top and bottom layers at 0.25mm layer height.
The middle assembly and lever can be printed slower and with a smaller layer height to get a more accurate part.