Snowdon Mountain Railway

[Michael GilliganParticipant @michaelgilligan61133]

Posted by john halfpenny on 01/12/2022 19:58:35:

Isn't the excessive smearing a function of the tooth shape of the cog […]

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I would say so … which is why I asked if there might be photos available

MichaelG.

[Neil WyattModerator @neilwyatt]

Posted by old mart on 29/11/2022 20:35:50:

The rack is made out of leaves

I can see that from the photos

[DC31kParticipant @dc31k]

Posted by john halfpenny on 01/12/2022 19:58:35:

Isn't the excessive smearing a function of the tooth shape of the cog, giving a sliding rather than a rolling contact

The patent to which Michael Gilligan linked further up in the thread has information on the geometry of the Abt system. It looks like a standard 14 1/2 degree pressure angle involute gear.

Also worth perusing is the Wikipedia link someone provided above, on rack railways in general. In there it says that one of the rival systems to the Abt (the one with back-to-back channel and straight teeth) claimed less rack wear.

[HopperParticipant @hopper]

Posted by DMB on 01/12/2022 19:12:14:

Hopper,

Whilst I agree with your last post, have another look at the photos. Both tracks appear to be buggered!

John

Yes agreed, But (hopefully!) both pinions will be intact and in much better shape. Tis the pinions that are the critical safety element. If the rack(s) let go as the loco is at the top of the hill, there is miles of rack between the loco and the bottom to slow it down. But if the pinion(s) lets go, there is no stopping the train until it either hits the bottom of the hill or derails due to overspeeding on route.

I wonder, could it be that this loco has been fitted with a modern 20deg PA pinion gear running on the old 14.5deg rack? You can get away with it on lathe change gears under almost no load, but not so much on a high load application like this.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Hopper on 02/12/2022 00:05:57:

[…]

I wonder, could it be that this loco has been fitted with a modern 20deg PA pinion gear […]

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That, Sir is the hunch of which I wrote

The special shape of Abt’s patented pinion tooth bears very little resemblance to a standard involute form.

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

[ sorry, duplicate posting ]

Edited By Michael Gilligan on 02/12/2022 00:22:11

[Michael GilliganParticipant @michaelgilligan61133]

[ sorry, triplicate posting ]

This forum software is driving me potty 

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Edited By Michael Gilligan on 02/12/2022 00:24:24

[SillyOldDufferModerator @sillyoldduffer]

I agree with those who see these rails as sacrificial. All machines wear out, and a rack railway passing (i guesstimate) a 50 ton train up and down a steep slope 4000 times a year is going to do some damage.

Wear is concentrated on the rack because it provides all the traction and braking, and it will occur most on the really steep bits. Given the drive wheels are expensive to replace, and lengths of rack are cheap and easy, it makes sense to sacrifice rack sections rather than fix the locomotive. Also, the safety of the system depends on the engine not jumping off the rack, which implies it's heavily weighted to keep contact as well as being held down by guide rails.

Anyone up for doing the sums? How much work is done per trip:

• assuming the train weighs 50 tons
• the railway is 7.53km long
• the average slope is 1 in 7.89, and the steepest sections are 1 in 5.5
• the average speed is 8km/h

And, assuming the bearing area of each tooth is 50x120mm, what pressure is applied to teeth on the 1 in 5.5 sections?

I suggest it's incorrect to think the Snowdon racks should look good. I think they're designed to last a certain number of lifts and then be replaced, sooner if inspection reveals excessive wear. Much the same is done with wire-ropes; they too have limited service lives and are treated as consumables. Their common-sense appearance doesn't matter: steel ropes can look OK from the outside but be cracked to hell internally. I think manky racks are OK too – provided they're still within specification.

Dave

[Michael GilliganParticipant @michaelgilligan61133]

Posted by SillyOldDuffer on 02/12/2022 10:47:34:

[…]

I think manky racks are OK too – provided they're still within specification.

Dave

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So … does anyone know the specification

MichaelG.

[JuddyParticipant @juddy]

I would imagine that they are not permitted to grease the racks because of contamination of the environment in a National Park, so lack of any form of lubrication will not help in the excessive wear.

[Stuart HarrisonParticipant @stuartharrison30824]

In the winter of 1955-6 we regularly descended Snowdon by sitting on a slate placed on the rack, whilst steadying ourselves by putting our boots on the side of the rails. I do not remember seeing such excessive wear of the rack as shown in the photographs. This wear may be due to the quality of present day mild steel compared to steel produced by the Hearth process.

Stuart Harrison

[Roger BParticipant @rogerb61624]

A chance to practice your German and some good pictures and diagrams of rack systems:

Zahnradbahn/Fahrwege und Fahrzeuge/ Wetzel (swetzel.ch)

Nothing looks as badly worn as the Snowdon example. There are ester based biodegradable lubricants that can be used even in Swiss Mountains.

[Michael GilliganParticipant @michaelgilligan61133]

Excellent link, Roger

Thank You

MichaelG.

[Author]

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