Thanks Oli.
I did the chimney work on a couple of lathes, one a Chinese mini-lathe (Seig SC3 with 7" swing) and the other one of the £30 or so micro lathes which consists of a horizontal motorised chuck mounted on an aluminum bed. I've amended the former to take a vertical slide and made a start on the base by using an 8mm diameter slot drill to form a curve. I then opened this out using 120 grade emery cloth wrapped round a drill shank, however I arranged for the diameter of the shank plus the thickness of the cloth to be the same as the smokebox diameter, so it sounds like I should have used a slightly bigger shank.
Given that I had a good drawing of the chimney (from one of Bob Essery's books) I should have been able to get the chimney diameter pretty well bang on, however it didn't work out that way as the cutting tools that I had were too large. I've now ground down an HSS blank to produce narrower RH & LH cutting tools so hopefully that will do the trick.
I used the latter micro lathe for manual turning with the chimney mounted on a spigot. I agree I didn't get the flare fine enough, reducing the drawing down to a 2mm size sounds like a good idea for the freehand work. I use a couple of square section gravers (plus various files) for the free hand turning resting them on a simple tool rest. This seems a bit hit and miss as despite trying to get the cutting point on the vertical centre line of the lathe and at a sensible angle I find that sometimes it cuts well, and other times it just rubs. I don't know if anyone has any tips?
Richard