Steel wheels on steel rails grip about as well as a shoe on ice. A normal train gives up at a few per cent; a rack railway climbs slopes steeper than a staircase by laying a toothed bar between the rails and giving the engine a gear wheel, a pinion, to climb it. The idea is simple. Making it work on a real mountain, in snow, round curves, through points and safely back down again, took a century of invention.
These nine chapters tell that story, with something to try in each: models built to the real dimensions from the engineering papers of the day. They run in your browser, and are best on a computer.
The chapters
1. The problem is grip
Why steel wheels slip on a hill, and how steep a train can climb on friction alone. Try the grip lab: make the wheels spin.
2. The people who climbed
Blenkinsop, Marsh, Riggenbach, Abt, Locher, Strub and the engineers who followed: who invented which rack, and why, on an interactive timeline.
3. The rack family
Six ways to make a toothed rail, from Marsh’s ladder to Strub’s milled bar, in 3D with a pinion rolling along each.
4. Inside the mesh
Why the teeth have the shapes they do, why one bar is not enough, Abt’s staggered bars, and the force that lifts a pinion.
5. Getting on the rack
A spinning pinion has to drop into teeth it cannot see: Abt’s sprung entry of 1885 and what came after, with a simulator to drive into the rack yourself.
6. Points on a mountain
How rack railways switch trains between tracks: moving rack, rack gaps, Abt points, transfer tables, the Pilatus turntable switch and the Rigi bending switch.
7. Engines that lean
Why mountain steam engines have tilted boilers: keeping the firebox crown under water on a 1 in 5½ climb.
8. Coming down safely
How rack trains brake on the way down: counter-pressure steam, pinion brakes and heat, and the Snowdon accident of 1896 step by step.
9. The lines
Fifteen real rack railways, from Pilatus to Pikes Peak, rebuilt from survey data and drawn to one scale, each with a link to drive it.
Try it here
The contents page, with its first model: drag the slider to make the hill steeper and see where the rack takes over. Follow any chapter from it, or open it full screen.
The railways in the last chapter can be driven: see Rack Railways. Questions, corrections or a rack railway you would like to see covered? Get in touch.