I've designed jewellery for my wife's last few birthdays. Nothing fancy, geometries, square kufic and such.

Very crude approach: I've been doing it in Blender, if you've 3D skills should be easy. I've got a friend who does the printing and casting, so there's more I could explore there later.

I also do dioramas, which grew out of 40K. Got bored with hench guys with guns and moved to 6mm, it's been great fun focusing on buildings.