This is another idea that springs from the increased rarity of metal, as well as the implementation of item quality.
Let's say you make yourself a nicer metal whatever, a pick, miners helm, hammer, etc. etc. What to do with the old one? Sure, you could sell it to another play... or?
Lets say you dump it in your smelter, and remelt it down into a bar of the same Q metal as before. Any wooden elements would be destroyed.