I modified mker17's Triangle Modular Spool Rack to use ¾" EMT conduit for more strength. His original frame pieces are sturdy enough, but found dowel rods load capacity to not meet my needs.  Rather than add more supports, I went with a more rigid shelf material.  The vertical supports are still ¾" dowel rods. Mine easily supports 10 fully loaded dry boxes or about 14-15 full spools on a 3¾ ft span without any noticeable sagging. This can be pushed a bit further, but I've not tested it yet.

EMT uses trade sizing, so ¾" is a bit misleading. The actual outer diameter is .922", so the frame models have been adjusted accordingly.  
I've made  the tolerances tight for a more secure fit. There are test prints included to check sizing.  The frame's support tier has slightly wider holes for the conduit, so that it can easily slide into place, even if painted.  I've left negative parts centered on each hole, which can be used to easily adjust to fit your machine or further expand to fit a wider diameter.

The original model was designed for securing the rods into the frame using screws, so I made a press fit plug for the hollow EMT conduit. The tighter fit for the rods ended up being secure enough for me, but still including these for anyone looking to make a truly solid rack.  It is made to fit a M5x8mm threaded heat insert.  These too have tight tolerances and will need to use a mallet to fully insert the plug flush. A heat gun will be needed if you want to remove it for any reason.

The rest of the setup:

• PRAKI cereal box
• Favorite Filament Sample Holder - PRAKI Cereal Box by me
• Favorite Filament Sample by GlennovitiS 3D
• Cereal dry box remix by jwnicholson