normally if a sub craft is required it has to be at least the level you need to be to craft the item youre using. So if you need to use darksteel materials you have have smithing high enough to make those materiels yourself, whatever level that is >.>
yeahhh, if only the recipe for darksteel chains didn't cap at 63. Lets follow your example to woodworking. In which making an Ox-Tongue, a lvl 100 synth, would require a subcraft from smithing of atleast 90.