For the 12 mm definitely go for a mag base. You don't need an air powered drill for those small bits... just a good quality electric at full rpm. I found labourers are brutal on small annular cutters. If you get a mag drill that cannot take a chuck then make up brazed bits like I suggested in the sizes you need. It is a lot cheaper than the cutters. A tip on electric hand drills: They expire because people abuse them. When you are done drilling a hole pull the trigger and run the drill flat out for five to ten seconds. The fan will cool the armature. If you don't then when you lay the drill down all that heat sinks into the armature windings and breaks down the insulation. This practice will significantly increase the life of your electric drill or any electric tool that has been working hard. Randy
Thanks. I don't have an air drill (because I haven't got round to buying a compressor yet, but it's on my "want" list). I just have an electric pistol-grip drill, and I'm rather scared of burning it out. A guide block is a good idea, so I might try making one for small diameter drills, but I still need to drill some 12 mm and 14 mm holes in 6 mm and
10 mm plate. This would be really hard with an electric pistol-grip drill, and I have a 230 V -> 110 V transformer which could run a magnetic drill, so you can see where my thinking was going.
Will think about it some more...