Big Boy Lateral Motion control

[Anonymous]

I've often run across references to lateral motion devices used on some of the drivers for Big Boys and other 8 and 10 coupled steam locos. I assume these are intended to allow some controlled lateral movement when rouding curves. What are they and how do they actually work? Are they located between the driver and journal box or the journal box and frame? Are different types used on locos with plain and roller bearings?

Big Boys also had a geared centering device between the front articulated engine and the boiler. How does this work and what other types are used on other articulated steamers?

[malcolmyoung]

Alco's Lateral Driving Box Cushioning Device, (as they called it) allowed a small amount of sideways movement of the driving wheelsets on curved track, the amount of movement differed on different axles. The cushioning was provide by large helical springs in front of and behind the axle (or cannon box in the case of roller bearings). These springs also centralised the axle in relation to the frames when running on straight track. The design differed slightly depending on whether the loco was fitted with Timken or SKF bearings. The Franklin Railway Supply Company, Inc. also manufactured similar equipment.

The different types of truck centreing devices included the gear type, the swing link type and the heart cam type. All of them worked by lifting the weight of the locomotive off the truck to the opposite side of the curve of the track and using gravity (the weight of the locomotive) to force the truck to centralise. These devices are difficult to describe without the aid of diagrams, a good source of which is 'Locomotive Cyclopedia' or 'Train Shed Cyclopedia' (Often available on eBay)
Malc.