I found that 28mm broomstick poles are the cheapest decently stiff round material I could buy so I designed hubs around those to create a filament rack that doesn't rely on wall attachments. It takes some time to print, but assembly is super easy.

It is probably best to print in abs/asa/petg, however since the forces are directly stacked on the broomsticks, the forces applied to the print are only limited to the weight of a single tray (divided by 4 for a single hub) therefore it should be fine to use PLA too.

Instructions:

I added 2 screw holes for each connection point, but in general, only one is used. the second one is so you can put in a screw from any side, which is useful when expanding a fully stacked rack, or one that has been secured to the wall.

For a basic one-segment rack you need:

• 2*180mm sticks per tray(horizontal spacers)
• 4*240mm sticks per tray (vertical spacers)
• 2* <1000mm sticks per tray (horizontal carriers
• 4 legs (I used the pointy end of the broomstick that was left after cutting the rest)
• 4 + 12 per tray 4*20mm wood screws (can be longer but not longer than 30mm)
• 4 per tray 4*40 wood screws
• 4 4-way hubs (printed) per tray
• 2 3-way hubs (printed) for the top. (or end in a 4-way hub if you have room to expand later)

For the assembly:

1. First, add the hubs to all the 180mm horizontal spacers, and secure them with a 4*40mm screw (put them in the shortest connection point)
2. Push in horizontal carriers and secure them on one side with 4*20mm screws
3. Make sure they are flush on a flat surface before securing the other side with 4*20mm screws
4. Add either legs or 240mm sticks to one side of the tray, and secure them with 4*20mm screws
5. When a tray is finished it can be stacked on the last one, the screws to secure these are actually optional