this is the 2nd version the one uploaded before is wrong.

in this version i have made it longer to span between 2 shelves in accordance with the dimensions given.

i was thinking by it spaning between the 2 shelves it would help distribute the Weight. this way you dont get alot of Weight twisting on 1 board. at least that was my thought.

added some spacers to bring it out past the spools on the shelves. this way if you have a full spool it can hang in the middlle and will not hit the filament.

i imported the model into Simplify3D to check if it fit the bed of a cr10. i have a cr10 but i am unable to print it at this time i dont have the filament right now.

it should inport in the position shown in pic.

you should be able to position it anywhere along the shelves.