I was doing it by hand, but I was also kinda making it up as I went along. I have since bought some small tool blanks, including a round one, which should make a difference.
I soldered them in place, but I think I will now need to make chimney number 5. The top flange is too big, which didn't really show up until I took a picture of it...
Do you turn up a deep base with the chimney / dome Gareth? This helps to give you material from which to make the flare. Your dome looks a bit impoverished in this area. The thick base can then have the diameter of the boiler / smokebox filed in to it so that the best fit is achieved - sometimes useful to use bar of the same diameter as the boiler for checking. Finally the sides of the flare are filed in or ground in with a bur/stone/abrasive polishing tip in the Dremel. I always use 24 hr Araldite to fix boiler fittings, soldering is far too tricky to get them in the correct place.