Abt rack system
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Image:SMR Axle on display at Llanberis 05-07-24 20.jpeg
The Abt rack and pinion system was devised by Carl Roman Abt, a Swiss locomotive engineer working for a Riggenbach-equipped line, as an improved rack system. The Abt rack features steel plates mounted vertically and in parallel to the rails, with rack teeth machined to a precise profile in them. These engage with the locomotive's pinion teeth much more smoothly than the Riggenbach rack system. Two or three parallel sets of Abt rack plates are used, with a corresponding number of driving pinions on the locomotive, to ensure that at least one pinion tooth is always engaged securely.
The pinion wheels can be mounted on the same axle as the rail wheels (as in the picture at right), or driven separately. The steam locomotives on the Mount Lyell Mining and Railway Company had separate steam pistons driving the pinion wheel.
The Strub system, invented by Emil Strub, is similar to the Abt, but uses just one wide rack plate welded on top of a flat bottom T railway rail. It is the simplest rack system to maintain and has become increasingly popular.
