In my blacksmithing, I have 2@1 use hammer skills. What if I were using the hammer for something other than its intended purpose? Like suppose I was trying to bludgeon someone to death with it? Do I still have 2@1 Use Hammer? And if so, would using one as a weapon count as a new use?
It will probably sound odd, but the division is between all tool uses of a hammer and all weapon uses of a hammer. There is also the matter of specialization to consider. Since your 2@1 hammer is connected to blacksmithing, it's 2@1 for hammering metals. It would be 1@10 for such hammer uses as quarrying stone, driving nails, driving spikes, and so on. But using a hammer as a weapon is a separate skill--it would be a blunt weapons skill, which would include using clubs, staves, morningstars, and similar striking levers, and would also include throwing such weapons. At 2@1 it would become specialization in hammer, with 1@10 in other blunt striking weapons.
The thinking is that using a lever to attack someone is much more similar based on the action to using different kinds of levers to strike someone (crowbar, pipe wrench, pipe, candlestick in the library by Colonel Mustard....) while using the hammer specifically as a tool is much more similar to using the same tool for essentially distinct tasks.
Also, when you were still an amateur at using a hammer, you could get skill marks in "Use Hammer" by using it to break stone or drive nails or whatever, but now that you are professional, such use would give you "Use hammer (carpentry) 1@10 +1 mark" or "Use hammer (stonework) 1@10 +1 mark", on your way to professional level in hammer use in another field.
Hope that helps.
--M. J. Young