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Comment by dotancohen | Hacker News Reader

  > The difference between Finnish and Russian gauge is 4mm

What is the acceptable tolerance? It doesn't sound like a huge engineering effort to design a boogie compatible with both without requiring switching.

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Train tracks are normally not precise to within 4mm anyway, and wheels are wide enough to tolerate that.

> Train tracks are normally not precise to within 4mm anyway

Yes they are. Of course practical tolerances including allowances for wear and there are large enough that things can be made to work, but in terms of nominal construction tolerances for example, 4 mm can easily eat up all your construction tolerances or even exceed them.

I obviously don't have a in depth knowledge of Finnish rail, but have you ever looked at rail in the US? I can show you tracks with completely missing ties. Tracks that move vertically by a foot when the train goes over them. Tracks that visually snake all over the place. The difference is made by slowing down the train. Derailment at 3 mph rarely matters. The biggest risk is the conductor doesn't know it happened & continues to drag the car along the tracks

Sure, but even in the US that infrastructure state is usually only found on minor branch lines (shortlines), not on the main lines.

There used to be a St.Pete-Helsinki high-speed train before the war, Allegro. It was built with bogies for a 1522mm gauge.

Yes, the acceptable tolerance is -4mm+7mm.

Where? Finland specifically, or elsewhere? Both my local tram system in Germany as well as DB as the national infrastructure operator in Germany have construction tolerances of only +/- 2 mm. Maintenance tolerances on the other hand can be quite a bit larger, at least in the plus direction (on the order of 15/20/25 mm).

Sure, but thats Germans. I'm surprised it isn't specc'd in 10ths.

They should've specced 1435mm±410µm, with no broadening at curves.

I just wish the Germans would be as accurate with their train schedules as they are with their rail gauge tolerances :D

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