Turnouts on a canted curve

[Derekstuart]

Could anyone possibly help me work out the following, please?

 

​I have built a C9 turnout with the main road on 30 chains (8135mm), following a Templot design so I know I have the two turnouts designed properly. From BRT tables I have worked out that for the line speed the cant should be around 4 inches for jointed track. I have reduced this to 3 inches as it's a nice round number for modelling purposes.

 

The diverging road will thus end up with a cant of its own, which isn't a problem but as it is on a curve it will start to 'dig' itself into the base board. I have worked out the following maths, but it is probably flawed.

 

Cant gradient across track is 1 in 19 = .053

Diverging road is 1 in 9 = .0058 (ie for every 1mm forward on the line the vertical movement will be .0058)

400 mm for cant gradient = 2.34 mm vertical movement over the transition of 400mm. Ie I need to have 2.34mm of cork that I can strip away in order to accommodate this.

 

Or is it all **** about face?

​Also, if it isn't pushing my luck: I built the C9 using Templot's curviform vee, as I assume that as it is going from a curved main road to a curved diverging road engineers wouldn't want to insert a short straight section.

 

Any comments would be appreciated. I know the real railways have this same issue and there are some good explanatory articles out there, but I'm damned if I can find them again.

 

Thanks
​Derek

 

 

 

[martin_wynne]

Hi Derek,

 

Look in your copy of BRT3 on page 148, Two Level Junctions.

 

The prototype used two-level chairs to correct adverse cant in curved turnouts. The special chairs were made with the base thickness increasing in steps of 1/12th inch or 1/16th inch.

 

Two-level flat-bottom baseplates are similarly available. A recent RAIB report into a derailment found that it was caused because after spot re-timbering of a crossover the two-level baseplates had been muddled up and not used in the correct sequence. It turned out that the privatised maintenance gang knew nothing about two-level baseplates. I doubt such a thing would have happened in BR days.

 

regards,

 

Martin.

[TheSignalEngineer]

 

 A recent RAIB report into a derailment found that it was caused because after spot re-timbering of a crossover the two-level baseplates had been muddled up and not used in the correct sequence. It turned out that the privatised maintenance gang knew nothing about two-level baseplates. I doubt such a thing would have happened in BR days.

 

Oh no? This connection looked innocuous enough but was on a transition with the line immediately after the crossing starting to drop away and with zero cant. After the pway had been doing a bit of work it ceasesd to be able to cope with 21T mineral wagons. 

 

 

 

To cap it the same thing happened again two weeks later.

[Fat Controller]

Hi Derek,

 

Look in your copy of BRT3 on page 148, Two Level Junctions.

 

The prototype used two-level chairs to correct adverse cant in curved turnouts. The special chairs were made with the base thickness increasing in steps of 1/12th inch or 1/16th inch.

 

Two-level flat-bottom baseplates are similarly available. A recent RAIB report into a derailment found that it was caused because after spot re-timbering of a crossover the two-level baseplates had been muddled up and not used in the correct sequence. It turned out that the privatised maintenance gang knew nothing about two-level baseplates. I doubt such a thing would have happened in BR days.

 

regards,

 

Martin.

Which one was that, Martin? One of the two near Washwood Heath, or the one at Reading West?

[martin_wynne]

Which one was that, Martin? One of the two near Washwood Heath, or the one at Reading West?

 

See: https://assets.publishing.service.gov.uk/media/568fd5a640f0b667f300000f/R012016_160111_Washwood_Heath.pdf

 

Paragraphs 107 on.

[Derekstuart]

Thanks Martin. As ever, your seemingly unlimited knowledge and generous use of your time, is much appreciated.

 

I did see that in the book but I didn't realise what I was looking at. (I know...)

 

So in effect I need to lift the stock rail by up to 1mm by inserting plastic/metal shims under the C&L functional chairs?

 

Thanks again. Now that I know what I'm looking for I will see if I can understand how the reverse works when it is on the outside of the curve (facing up), without having to ask daft questions.