Grinders are a welders best friend.  We like to use 4.5" or 5" angle grinders for most of our fabrication work.  These grinders are cheap enough at Harbor Freight Tools (sometmes less than $10) that we usually have 2 of them set up, one with a grinding disk and one with a flexible sanding pad and an 80 grit sanding disk.  We will do the majority of our grinding with the grinding disk and then finish off with the sanding disk so as to avoid taking off too much material.