If a 1-2-3 block is good then a 3-6-9 block must be three times better! This was mainly just me playing around with OpenSCAD but I figured I'd upload it in case someone is crazy enough to make it.
Note that the included SCAD file can be used to make more reasonably sized versions like a 1-2-3.
Created in OpenSCAD (source included). The length of each side, the hole diameter and the number of holes along each axis are adjustable parameters.
Are supports needed? I hope not ‘cause it would be a pain to dig them out of the center of this thing. Run with whatever nozzle diameter and layer height you feel like.
Load up a completely full spool (at least 1KG), start the print and go on vacation for a week. When you get back it should be done.
The author marked this model as their own original creation.