I've made some more improvements to the hanger. I put some recesses on the forks to take some self adhesive 3mm foam so the Uke neck and head arent damaged and wont slip on the slippery pla plastic.
I also enlarged the holes of the piece that fits on the music stand. So rather than a tight fit I left space so some of the self adhesive foam can be stuck to the inside which will hopefully provide grip and prevent the thing from sliding down when weight is applied.
It should also be squishy enough so other sized music stand diameters can be accommodated.
It's printing now so tomorrow we'll know if my calculations are even close.
Due to the sponginess of the foam it may make the forks point down slightly so I may need to go back in and angle the forks up by a few degrees so it compensates for the weight forcing the hanger to point down.