The most significant item to have been manufactured recently is the smoke box door. Tornado’s smoke box door started life as a spun tank end which gave the dished shape. The sharper radius on the outside edge of the door was achieved by hand forging over a former. The “D” shaped smoke box door on the original P2 design does not lend itself to this method, although it would be technically possible to achieve it by cutting, black smithing and welding the round door, however with the smoke box door being both a prominent and iconic part of the P2 design, there was doubt that a satisfactory finish could be achieved by this method.
Other methods considered including CNC machining the door out of solid 8″ thick plate, however this was significantly more expensive that the method actually used. Having seen the quality and surface finish that South Devon Railway Engineering (SDR) was achieving with firebox back heads, throat plates and tube plates, they were asked to quote for making the smoke box door. After some discussion an acceptable quotation was received and male and female press tools made using the 3D CAD model.
Male and female smoxebox door formers at the SDR – David Elliott
Following a trial pressing in mild steel, the definitive smoke box door was pressed from Cor-Ten steel – the corrosion resistant steel used on unpainted metal bridges and sculptures such as the Angel of the North. For the first stage of pressing the plate was clamped flat over the female press tool and the domed male press tool pushed downward to dish the plate. The plate is then unclamped and re-heated and the flange round the edge of the door formed by pushing the male tool right through the female tool. The wavy edge is then cut off to leave an accurately shaped pressing. Sarah Anne Harvey’s photos show the process: