The smoke box is sheet metal 3/32″ thick and 6 1/2″ outer diameter. I could not source tube of that size and ended up having it rolled and the seam tig welded by a local firm.
It fits the saddle neatly and just clears the expansion link as it should.
The steam pipe connections to the cylinders are my first real job in this section. They need to be made so I can connect an air supply to assist in setting the valve timings.
There is no dimensioned drawing of the steam pipes other than the flange that bolts to the cylinder and a note to use 7/16″ OD by 20g pipe. There is a general arrangement view of an end on front view of the cylinders that depicts the pipes and it shows the outside cylinder pipes vertical from the cylinder and then bent in through the smokebox and the inside cylinder at a very slight angle towards the right hand cylinder.
Looking at the full size A1 the outside steam pipes are encased or clad and the casing is at an even angle from the cylinder to the smokebox. I need to find out a bit more and decide if the pipes need to be as drawn or put at an angle direct from the cyinder.
The connecting flanges are made from PB and consist of an rectangular slab held in place by four 3 BA set screws to the cylinder block with a 1/8″ deep pip to fit into the cylinder block steam hole and a 7/16″ dia recess to accept the steam pipe silver soldered in place.
The connections inside the smokebox are a screwed union but there are no drawing details for their manufacture so I have to design my own.
A couple of sleeps and a bit of thinking and I have decided that the steam pipes have to be made as drawn as to make them at an angle would bring them too low in the smoke box as the flanges are close to the frames. So to make the external steam pipes look similar to the full size the cladding will have to be made so it slopes at the right angle and encases the steam pipe. An added complication is the steam oil injection is at the back of the steam pipe so the cladding has to have a cut out to accommodate that. I can see lots of of paper/card formers being made!
General arrangement of steam poipes. On the right is my pencilled form for the cladding.