Snowdon Mountain Railway

Walked up Snowdon (Yr Wyddfa) today with a couple of pals. Fabulous walk and lovely weather.

Coming up the Pyg Track we came to the Snowdon Mountain Railway track and I was astonished to see the wear on the rack. Whether this is one season's worth or more I don't know. There was a gang out lower down the mountain working on the track and I assume/hope they were replacing the rack.

I thought folks might be interested to see the extent of the wear.

Looks like someone has placed fallen leafs on each tooth.

I live in Switzerland and travel fairly often on rack railways. Generally they are well lubricated and I have seen nothing like that

Or someone has been welding with a material that has spread under load?

One might wonder what the loco drives are like?

BTW, it’s not (or won’t be for long) called Snowdon.  Too English, for the Welsh, apparently.🙂

Edited By not done it yet on 29/11/2022 20:02:18

Perhaps it was the hot weather we had. Oh forgot Snowdon is in Wales.

The steel that the rack is made out of leaves a lot to be desired. I wonder if the sections were originally made with a symetrical profile, so they could be turned round?

Worked with a Guy, His side work was welding rail up, sidings to factories,etc. Seems cheaper to replace rail rather than weld.

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Eeek !! … or words to that effect

Is it lousy modern material, in ‘pattern parts’ or have they increased the loads to such an extent that the design is no longer fit for purpose ?

I would love to see the original design specification.

MichaelG.

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Edit: __ possibly an interesting page for those who know about such things:

https://snowdonrailway.co.uk/abt-rack-railway-info/

Edited By Michael Gilligan on 29/11/2022 21:57:24

Gear tooth profile aficionados might like to download this patent: **LINK**

https://worldwide.espacenet.com/patent/search?q=pn%3DGB189608084A

[ Click the three dots to access the download link ]

MichaelG.

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Edit: __ Next time you are up there, Ian … could we have some photos of the pinion teeth, please ?

[ especially on the modern locomotives ]

… I have a hunch. 

Edited By Michael Gilligan on 29/11/2022 22:15:03

This is a photo of some bits of rack lying at the side of the track around half way down. I imagine they have a specification indicating how much wear can be tolerated before replacement, and an inspection regime to check the condition of the rack through the operating season.

Looks like the rack is sacrificial soft iron, almost a consumable

Edited By Ady1 on 29/11/2022 23:46:24

Thanks for the link.

Can I just quote one paragraph for reference:

"The rack at Snowdon utilises a pair of toothed racks offset by one tooth and two driven axles on each locomotive, each axle with a pair of pinions. This ensures that there are two teeth fully engaged at all times to increase safety. The braking system also uses the rack to slow and stop the trains with the brakes fitted to the pinion axles on the locomotives and carriages."

If they are offset by one tooth, I think the rack teeth would line up. They do not seem to do so in the picture. Might it be better expressed as saying they are offset by half a tooth?

Thinking about the engineering behind this, the axle spacing of the locomotive would also have to bear some relationship to the rack tooth spacing for the double engagement to work. I wonder if you made the axle spacing adjustable, it could act as an anti-backlash mechanism. The (keyways in the) pinions would need to be clocked relative to each other.

Note in Mr Abt's patent, lines 15-20 his discussion of the tooth inclination (1 in 4). I think that gives the standard 14.5 degree pressure angle. It is widely remarked that this angle was chosen for gears because its sine is 0.25 or 1 in 4 (apropos nothing, it is also recommended that you erect a ladder at this same slope - 1 in 4, often noted as the complement, 75 degrees).

There are modern developments in gear technology which use asymmetric gears which might have been helpful to the wear issue had it been around at the time the system was invented.

https://gearsolutions.com/features/the-benefits-of-asymmetric-gears/

I had a look through my pictures to see what racks were fortuitously there. There is one of the depot at Vitznau and one on the Geisbach railway. Both are Riggenbach and virtually unworn. The rusty pictures are slightly confusing. They could be the points section of a Riggenbach system or an Abt system.

Having the parallel pair of racks with the teeth staggered by 1/2 a pitch and the twin gear wheels underneath the locomotive also offset to match makes a smoother drive

This one seems to be a bit different, the Budapest Cog-wheel Railway, is a rack railway in the Buda hills part of Budapest. It connects a lower terminus at Városmajor and with an upper terminus at Széchenyihegy. The line is integrated into the city's public transport system as tram line number 60, is 3.7 kilometres (2.3 mi) in length, rising some 264m.

Coming into the station.

The rack

The drive system consist of a single rack and wheel. It uses the Strub cog-wheel system. (the link is to Wikipedia) The wheel & rack display seems to have a slightly different construction to that actually fitted between the rails (might be an earlier version)

John

Edited By Journeyman on 30/11/2022 18:56:47

Visited the Vitznau Rigi Railway about fifteen years ago, the following may be of interest.

Rob

Well, apart from a minor mishap on opening day in 1896 when an apparently overloaded loco lost control on the way down, and having been abandoned by its crew, fell off the mountain! The coaches stayed on the track only to be hit by a following loco.... **LINK**

....the railway seems to have an excellent safety record, so we must assume the team up there know what they are doing.

It does look like the relatively soft rack is allowed to wear away protecting the hardened pinions on the locos which must be expensive and tricky to replace.

.

… and I would be very interested to know the material specification for that rack, and how [if at all] it has changed over the years.

MichaelG.

This was the Snowdon Railway track in 2015 (you should be able to click for a larger version):

(Please forgive the black and white - I was playing with a new camera)

Edited By Andy_G on 01/12/2022 10:14:42

Edited By Andy_G on 01/12/2022 10:15:34

Thanks for sharing that photo, Andy

Monochrome suits the subject very nicely

Foreground detail usefully shows some ‘smearing’ of the metal already.

MichaelG.

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Edited By Michael Gilligan on 01/12/2022 11:52:14