British Railways Mark 1 - Construction

Construction

The design was used for hauled passenger stock, multiple unit carriages and non-passenger carrying stock. For passenger stock, construction continued from 1951 to 1963, while multiple units and non-passenger carrying stock continued to be built until 1974.

These were constructed in two lengths. Most had underframes 63 ft 5 in (19.33 m) long, with bogies at 46 ft 6 in (14.17 m) centres; the body was 64 ft 6 in (19.7 m) long if the coach was gangwayed, or 63 ft 5.75 in (19.35 m) if non-gangwayed. A smaller number had underframes 56 ft 11 in (17.3 m) long, with bogies at 40 ft (12.2 m) centres; the body was 58 ft (17.7 m) long if the coach was gangwayed, or 57 ft 1.75 in (17.4 m) if non-gangwayed. The shorter vehicles were intended for use where the track curvature was too tight to accommodate the longer vehicles, due to excessive overhang.

These lengths allowed for compartments or seating bays 6 ft 3 in (1.91 m) wide, plus space for toilets and entrance vestibules; a typical design of Mark 1 vehicle, the TO (Open Third class), had eight seating bays, three entrance vestibules and a pair of toilets at one end. This provided reasonable space. Care was taken to ensure that passengers could enjoy an unobstructed view out of the train from all seats. Seats were aligned to windows and on the long-distance design of Mark 1, the windows had a low sill, just 25 inches (640 mm) above the floor.

An unusual feature of the design was the bodyside curvature, of 28 ft (8.5 m) radius and just noticeable; the windows had flat glass and consequently the upper quarter was separate and in a different plane from the lower glazing, with an intervening transom, and the steel panels were recessed on either side of each window opening to accommodate the difference between the flat glass and the curved sides. The opening portion of the windows were provided with sliding ventilators, with an external aerofoil for draught-free ventilation, the correct opening position being marked by a pair of arrows. Doors were provided with frameless droplights manufactured by Beclawat; these were supported by a spring-loaded lazytongs mechanism inside the lower part of the door, and the top of the window had a sprung metal clip enaging in slots on either side of the window opening.

The original vehicles had timber veneer interior finishes, and on the main line vehicles small plastic labels were fixed to the panels, giving the type of wood and its country of origin e.g. "Crown Elm Great Britain"; "Lacewood Great Britain", etc. In 1955, an order was placed for 14 vehicles, with manufacturers being invited to incorporate innovative features; perhaps the most striking of these prototypes, which were completed in 1957, were those constructed by Cravens. Following evaluation, and with the increasing influence of the British Transport Design Panel, Mark 1 vehicles built from the later 1950s onwards were to modified designs. Laminates were used instead of timber panelling, and in the very last of the Mark 1 hauled vehicles, fluorescent lighting was fitted instead of tungsten bulbs. An important variant on the Mark 1 design were the 44 Pullman vehicles built by Metropolitan-Cammell in 1960. A further change introduced in the late 1950s was the use of aluminium window frames instead of direct glazing into the steel panelling.

The underframes consisted of a heavy assembly of steel sections, with angle used to form bracing trusses. These were placed close to the centre line of the vehicle rather than beneath the solebars, as was characteristic of previous vehicles. The original bogies were a double bolster type, which like the coaches mounted upon them, were designated "BR Mark 1" (BR1 for short). These proved unsatisfactory and a new cast-steel design was introduced from 1958 (often referred to as the Commonwealth type). This gave a superb ride with minimal tyre wear, but was heavy. The final batches of locomotive hauled Mk1s, and many Mk1 EMU vehicles, were built with the Swindon-designed B4 bogie. Later on, many BR1 bogied vehicles were retrofitted with the B4 bogie, and a comfortable ride could then be relied on, as was evident in the later EMU vehicles.

An important factor was the compressive coupling, which provided excellent inter-vehicular damping through the gangway end-plates, which quickly became highly polished, indicating that they were performing this task.