The Burrell chimney cone should really be a rolled sheet metal part with an upper and lower cap. The lower cap being the interface to the smokebox. The upper cap being a brass ferrule that has a wide flare. However, at 1/20th scale and just 58mm long including both the top and bottom caps this felt difficult. Therefore, I went to a piece of 3/4″ round mild steel as a starting point.
First I drilled a 10mm hole through the centre, the narrowest outside diameter is 12.4mm and so this would give me a wall thickness of 1.2mm.
I set the 2.5° taper up on the top slide of the Warco lathe. This took a bit of judgement as the divisions on the rotation of the top slide are in 2° increments. This meant that I needed to check the taper I was cutting at two points just to ensure I was getting the correct angle. Thinking about it now I should have checked this on an offcut of material.
I machined the outside taper first and then the inside taper. This meant I struggled with chatter, a large offset on the tool and a thin part gave little strength. Looking at it now I should have turned the inside taper first. However, nobody will see the inside finish as much as the outer, maybe I got it right.
There is nothing more pleasing than putting parts together and admiring your handiwork. I think the Burrell chimney cone is actually looking rather good. Now for the brass ferrule/finial/pot….
Machined a brass ferrule (not sure this is the correct term?) for the top of the chimney, this is 24mm in diameter and has a 12.7mm hole through the centre.
This was then silver soldered to the steel barrel and then machined again.
There is a slight line where the joint is, but this will disappear once it has been painted.