Building Bridget Part 4

Building Bridget Part 4

The smokebox

With Bridget both the steam supply and (obviously) the steam exhaust pass through the smokebox so it is necessary to get the smokebox in the right position before the appropriate steam plumbing can be put in place.

The steam supply will come from the superheater tubes into the steam column, a vertical gunmetal manifold that passes through the bottom on the smokebox and then out to the cylinder steam chests. The lubricator injects steam oil into the very bottom of this column so that it is carried into the cylinders. This is a reasonably straightforward machining job with some copper pipework. The supply pipes have to bend through a pretty sharp right angle as they go over the frames and on to the top of the cylinder. I found this pretty hard to do well and, in the end, made a deep groove in a piece of round bar and worked it round as best I could with lots of annealing.

The exhaust pipes are much more of a challenge because they have to be silver soldered together while in place between the cylinders and the smokebox in order to have any chance of fitting and sealing. More of this later.

The core part of the smokebox is a piece of 6 inch diameter steel tube and I was pleased to discover that this is easily obtainable from my local metal supplier. Photograph 27 shows this piece of pipe cleaned up, machined to length and with the steam exhaust and flange fitted. I also drilled the rather large hole on the top for the chimney. Obviously, you can’t use a pillar drill to drill these. I mounted the piece horizontally on a boring table on the lathe, drilled each hole and then bored out the chimney hole to the required 40mm diameter.