Modular Filament Spool Shelf

I don't have enough room for a horizontal spool shelf, so this is the solution I came up with. The pillars and legs are printed in PLA. The wooden shelves have a thickness of 8.5mm. All the other dimensions can be found in `shelf.pdf`. On top you can add as many levels as you like.

There are three files with different heights of the pillars: 65mm, 75mm, 85mm
and two files with different heights of the legs: 41mm, 20mm