7 1/4"g Compound locomotive

Benbow

Design work was started in 1998 using works drawings and photographs for an Alfred the Great class locomotive as a basic source of information but with much help from expert friends, the LNWR Society and the National Railway Museum at York. Where possible I have tried to keep the model as a close scale repilca of the original, only deviating where its performance as a working locomotive might be compromised. The design work and drawings are not yet complete but progress in step with the construction of the model.

Double leading truck

The completed double leading truck

Double leading truck

The leading truck is of unusual design, not pivoting as in a more conventional bogie type but sliding from side to side guided by the large curved slot on the underneath.

Driving Wheels

The first parts to be made were the wooden patterns for the wheels, which were cast in iron at a local foundry and are the only castings used on the model. Steel tyres have been fitted to all wheels.

L P cylinders

The first cuts are taken on the large block of cast iron that will eventually become the low pressure cylinders.

Machining HP cylinder
Part machined HP cylinder

One of the high pressure cylinders ready to be profiled. Machining cylinders from the solid is simpler and cheaper than making patterns and having castings done.

The exterior profile of a high pressure cylinder being chewed out of a block of solid cast iron using a big carbide tipped cutter on on my old XYZ 1500 mill. Despite conventional wisdom to the contrary I find the use of suds on cast iron works well.

Profiling HP cylinder

Machining the outside on my old Bridgeport interact milling machine.

Machining HP cylinder

Final profiling of the high pressure cylinders

Outside crosshead

The outside cylinder crossheadsare built up from three parts and run in hardened and ground guide bars.

H P con rod

A close up of the outside cylinder big end.

Benbow

The valve gear

Crankshaft

Eccentrics are not needed with Joy valve gear so a substantial centre bearing is fitted to give extra strength.

Tender parts

The first parts of the tender chassis

Slide shaft
Slide shaft 3

The slide shaft for the low pressure valve gear was machined from a single lump of mild steel. The die slots were machined from S G cast iron and then bolted in place.

P1030696

To the left a view with the boiler set on the chassis for the first time.

The boiler is designed to operate at 150 lbs per square inch, a lot higher than most models, but being a compound this is required.

Below a view which shows the complicated screw reverser that will allow independant adjustment of both sets of valvegear.

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