Update 1: Extra Thicc - Added a thicker version for use with 1 inch diameter wood dowels.
There are a thousand spool rack prints out there, but most seemed too flimsy or focused on aesthetics rather than function for my taste. So I made one thats thick and blocky and strong, with holes for #6 wood screws to fasten to ¾" (1.9cm) diameter wood dowels.
As pictured, I used 22.5" (57.15cm) long dowels for the spool rails, and 9.75" (24.76cm) long dowels for stacking another module on top. I have stacked the rack 4 modules high with no issues but I would recommend using lots of walls in your print if you're planning to go that tall or taller. You might want to use a 3rd support in the center if you decide to make the rack longer than 36" to prevent the wood dowels from bending/spreading under the weight.
I also put receptacles on the bottom for office chair wheels to pop into, assuming they're standardized. Otherwise you can use the dowel holes to come up with your own feet/wheel attachments.
STEP file included for those that want to modify the design.
I personally printed this in PETG with ~6 walls (0.4) and 10% gyroid infill laying flat. Please don't print this with 2 walls and try to build an 8 foot tall rack. Printer discretion advised.
The author marked this model as their own original creation.