Expandable Spool RackI created this rack specifically for those 5lb/2.3kg filament spools that our filament usually comes in.This stand is modular in that you can extend the width of your rack by using longer rod and printing more of the arms.The arms are also ready for mounting upside down, i.e. under your worktable using M4 bolts. Good for those of us with limited workspace.OpenSCAD files have been provided so feel free to modify it anyway you like.Print a minimum of 2 of the arms to hold up a fully-loaded spool. Print more and use a longer rod to put together multiple spools on this rack.You will need to provide your own smooth/threaded rod, and some way to secure the ends so that the spool won't fall off. I had some spare smooth rods and hubs with setscrews that did the job; I expect that allthread and jam nuts will work just fine.x3 M4 trapped nut slots have also been provided per arm, this is useful if you're bolting the rack from under your work table (see photos). This was the original intention of my design, but you can use this as a free-standing rack just as well, as seen in the photos.For the spool hub, garden-variety 608ZZ bearings are recommended for press-fitting into the hubs, which can then be nicely press-fitted into the filament spools themselves. This is probably personal preference, but I find that spools on ball bearings work better for my setup, it minimizes any tension that the extruder has to overcome trying to yank filament off the spool, and lets the extruder concentrate on its job. YMMV. Use a bench vise to get uniform press-fits, a rubber mallet and some careful tapping will do just as well.Print tips: Using an infill of 15% honeycomb in slic3r works well, you won't need to go denser than that, unless you want a really beefy stand.