Exhaust Steam Spider
For most of the photos on this page, you can click the image for a larger picture.
This page is the story of the making of the exhaust steam spider. You don't see this component mentioned in locomotive books. The spider is used in outside cylinder locomotives and performs the same function as the exhaust manifold in a car in that it provides a passage for the exhaust gases from the cylinders. Like a modern car (with turbocharger), the exhaust gases are used to improve the efficiency of the engine.
In the photographs you can see the 2 main frame plates (in grey) standing vertically. The red block between the frames is the fabricated smokebox saddle/frame stretcher and cast exhaust steam spider. The spider is cast first and then it is welded into the smokebox saddle/frame stretcher.
Normally the spider would be cast in the normal way, i.e. make a wooden male pattern, pack foundry sand around it to make a female mould and finally pour in molten metal to produce the component. See the cylinder page for a fuller explanation.
A wooden pattern had been built but this had suffered from years in storage so, in late 2015, a decision was taken to explore alternative methods of producing a new one. A new technology has emerged, that of sand printing. Sand printing is similar to 3D printing in that a specialised 'printer' prints layer of sand and resin and produces the female mould directly from the CAD model.This type of casting is cheaper for one-off parts, like the exhaust steam spider. For parts like the outside cylinder, where the pattern can be re-used, conventional wooden patterns are cheaper. We believe that this is the first time any large major component has been produced, using this method, in the history of British Steam Locomotive building.