It doesn't seem realistic to completely lose the material of a tool once it's 'used up', except of course for stone tools. Metal tools have almost always been recyclable to a certain extent, however, because they can be melted back down, recast, and reforged. Now, it wouldn't be game-balanced to simply reuse the same ingot over and over again for the same tool over and over again, however, It 's also realistic for the material of a tool to degrade or wear away. To this end, I suggest allowing metal tools to be remelted in the forge - bringing them up to the liquid point - so they can be made into new tools. I also suggest having them pass only about half an ingot's worth of material. From a game-fun point of view, this retains and perhaps heightens the realistic simulation that TFC is supposed to present, and allows players to not lose as much of the work they've put into accumulating rare resources for advanced tools. From a game-balance point of view, you're still not allowing players to extend resources infinitely, and this doesn't disrupt the tech tree. This suggestion could also work in concert with other suggestions for extending tool life through maintenance, and so on.