I'm looking at starting the boiler for the hudson at the moment the tube for the barrel is to hand and needs splitting to form the crown and sides how do people recommend doing this.. somehow I don't think a angle grinder would be ideal
I assume that your boiler design requires the sides of the firebox to be longer than can be accomodated by the partial circumference of the barrel, so your longitudinal cut would need to be offset from the circumferential cut that allows the sides to be formed, one longer than the other. The shorter side requiring a piece of copper plate rivetted and silver soldered to it. The cuts can readily be made with an hacksaw.
Built 3 1/2" Gauge LBSC's LMS Black 5 Doris and Martin Evans Rob Roy Building Don Young's Black 5
I tend to make the shell in two pieces - the barrel and a separate firebox wrapper joined with a ring inside. I don't like jointing straps on the firebox sides - especially if they are put inside where they can restrict the circulation in what is already a narrow water space.
An alternative to a joint ring is to have the firebox wrapper overlap the barrel if there is room for the slightly larger outside diameter.