10: saddled up

The half-saddle is fairly complete now. From the outside it doesn’t look like much. There is a half-cradle for the boiler (smokebox), a bolt-tab at fore and aft to receive the other half of the saddle, and steam/exhaust ports.

With the x-ray vision, changes are more obvious.

The cast connecting the boiler to the cylinder has 3 ports running through it: the exhaust port in the middle, straddled by 2 steam pipe on either side.

The front view above shows the 3 ports running from the inboard end, curving down and running outside, and up again terminating at the cylinder.

The side view above shows the ports lay out. What looks like 2 “eyes” are the steam pipe, and the “nose” in the middle is the exhaust.

For comparison purposes, here’s a cross-section plan I referenced, taken from Meyer.

In Fig 13, label “J” marks the steam pipe, and “K” the exhaust.

Much of the time I spent making this part was just trying to visualize what is happening inside the cylinder and casting. Before CAD was invented, these old plans try to compress as much information as possible into few drawings. The practice these days is to have many drawings to communicate the idea, since producing drawings is much easier now.

And of course, they did not make 3d sections either.

But when everything is drafted correctly, it’s quite obvious! Here’s my 3d section through the middle of the saddle. In this section, the exhaust port is shown. Compare its similarity to Meyer’s Fig 13 above.

And below is a section through the 3 ports at the cradle. The middle is the exhaust. The long pipe above it splits the incoming steam pipe into 2 branches, terminating at fore and aft of the cylinder, supplying the steam to the steam chest.

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