New Ground Level Bogies update.
Another milestone has passed, with the Hayes 210M brake callipers and PNP actuator now installed on the first bogie. Note how the David Hudson self-steering layout eliminates the traditional central bolster and pivot, making it possible to fit the disc brakes and the vacuum gear on the bogie centre line. This makes the whole unit self-contained, which would be difficult to achieve with earlier forms of bogie construction.
Ron James and I have finalised the brake linkage after much thought and a few false starts. A number of improvements have been made over the Mk I and Mk II iterations in developing this Mk III production version:
- Brake Lever Extensions secured with ¼” pop-rivets for improved head clearance.
- Brake Lever Extensions have an extra tapped hole for the actuator connecting rod ‘big end,’ to improve the geometry and eliminate clashes.
- Coupling rod is now solid; adjusters were found to be superfluous.
- Brake adjustment and balancing is now exclusively by means of the castle nuts on the callipers (as designed).
- Split pins on the castle nuts replaced by R-clips for ease of maintenance.
Experience with our Mk I and Mk II Hudson-James bogies has shown that very little actuator force is required. The design challenge in fact is to minimise wheel locking, particularly when vehicles are lightly loaded; hence the intentionally short lever arm for the ‘big end’ of the actuator con rod. However to ensure good performance when fully loaded, all carriage wheels will be braked, so this gear will be fitted to every new bogie, and eventually retro-fitted to unbraked examples of the previous Marks.
As a further control, we will be standardising the train vacuum after trials, and fitting limiter valves to prevent the standard vacuum being exceeded.
Our next step is to replicate this bogie so that we can install the pair to refurbished carriage no 201.