Catch Me Who Can

The 5" Gauge Model

The Kinver and West Midlands Society of Model Engineers were approached about running trains on a portable track at the 'Trevithick 200' gala and agreed to do so. The society also decided to build its own working replica of the locomotive in 5' gauge and run it on a fifteen foot diameter raised circular track at the gala. We were there, engine was running and a tour of the ME Exhibitions is planned. What follows is an account of the project.

Discussion was held to outline how to build a model that, whilst accurately portraying the original would actually work in such a small gauge. The firing; valve gear; boiler pressure; type of track and method of operation was taken into account. As the plateway of the original pattern would be hard to reproduce, it was decided that the locomotive would run on conventional rails, as per the replica. The original boiler was a single return flue type and it was felt that this would not generate enough steam in this gauge. Kinver member and professional boiler builder John Ellis designed a multi tube boiler that is coal fired from underneath, the firebox being between the axles. The boiler was pressure tested to 160 psi which means that the model runs safely run at 80 psi.

The next problem to be overcome was the design of the cylinder and valve gear. The original locomotive had a cylinder diameter of 6' with a plug type valve operated from a beam by a bash lever. We felt the need to increase the size of the cylinder from a scale 1/2" to 3/4" in order to increase the power required to carry this single cylinder engine over its dead centres. In consideration of the valve gear it was felt that in 5' gauge, this would not be very robust and would be difficult to replicate. We designed a slide valve arrangement driven from the front axle by a single slip eccentric. This is hidden from view by the footplate. The setting of the valve of course needed to be correct for practical purposes and to help the engine to run as evenly as possible. The valve was given 0.020" lap with minimum or no lead and the locomotive needs to be pushed in order to get it to go in the right direction. The valve cut off is estimated to be around 95% as, like the original it was not designed to work expansively.

The wheels were cast from a pattern provided by another member of the club, professional locomotive man Dan Jeavons. Eight wheels were cast, four for the engine and four for the landau to be pulled behind it. The locomotive's water supply comes from a beam driven pump mounted on the side of the boiler. This pump incorporates a bypass valve, the water coming from and returning to a tank mounted in the base of the landau. A hand pump is also provided in the landau to give an additional method of supplying the boiler with water. As it happened, the beam driven pump was not very successful on the day so it was a case of catch the loco if you could and pump...more work required!!!

Due to the position of the firebox the wheel sets could not be mounted on the boiler, so a small frame was made to support the boiler, ash pan and grate. The front pair of wheels is allowed to pivot on a pin fitted to the front of this frame.

Now it is time to say particular thanks to some who have contributed towards the project to date. To Terry Harper who has provided all of the drawings and done a lot of the design work using C.A.D. modelling. To Mike Stevens who has made a superb job of the cylinder. To Mike Harrison who has drawn the short straw in putting it all together and making it work and of course to John Ellis and Dan Jeavons for their contributions mentioned earlier. Other unsung heroes include Allan Cookson, Eric Lumas, Pete Dawson and Roger Byran (who made a beautiful job of the track). Sorry if we missed anyone but...'Thanks chaps!'