Really interesting concept.
I would recommend having the voxels not be cubic (1x1x1) but rectangular with one dimension being smaller than the other two to better present the “density” dimension (for example 1x0.2x1).
This would allow things to look better and more diverse, players could for example carve a symbol into the side of an axe head if they wanted.
The crafting of those parts would also be a little better with a flat side. I once did a prototype for a smithing system for the game Vintage Story, which would have allowed crafting of such voxel shapes like tool heads. The prototype is standalone and not a mod for that game so you can try it: https://cdn.discordapp.com/attachments/351624415039193098/372770900799389696/SmithingPrototype.zip