Perhaps blacksmithing would be a \"general skill\" and weapon crafting and repair would be \"subskills?\" Here\'s how I envision something like that working:
General skill: Smithing
subskills: smelting, weapon repair, armor repair, weapon crafting, armor crafting,...
You have to have at least two general skill levels before you can train in subskills. Your skill in using the skill = [ general skill + appropriate subskill ].
Why take the subskill when leveling the general skill will have the same effect? Easy. Make the subskills two-thirds (or so) easier to train.
Why not specialize and become really good? Make an upper limit for subskills, like the subskill cannot exceed 3x the general skill level. Do you really think a master armormaker can\'t do general smithery? I find that hard to believe. I also think crafting/repair skills need to be kept close as well. How many swordmakers can\'t fix their own work? Not many. Whether or not they WILL do it is a different story.
This same gen/sub system could be extended to other crafts as well:
Textiles: weaving, taning, dyeing, leatherwork, hidework, woolwork,...
Carpentry: Framing (housemaking), cabinetry, furniture, carving, cooperage (barrelmaking),...