I decided that the original design for the idler pulleys on the X and Y axis did not allow much control over the tension of the belts, and then I'd have to resort to tension springs in order to keep the belts tight.
I hate tension springs.
So I designed a new system using aluminium angle pieces and some screws.
It is designed to hang freely, only attached by 2 tension screws that can be adjusted to tighten or loosen the belts.
Due to it's design, it will self straighten once the belt is attached.