Howdy neighbour, first things first, welcome to this site. I have several electric sheet metal shears, Milwaukee brand. I use them in my barn building business. They are supposed to be good for up to 16 or 18 gauge steel. I use thinner steel in my work, 26 - 29 ga. They would be hard pressed to do a good job on 18 gauge and depending on the hardness of the steel, they won't last long. I have tried nibblers as well, but I always stuck to the shears.
