Advice on Turnouts: Size of Vee and Planing?

[polybear]

Hi all,

What are your thoughts on minimum(?) turnout V angles and switchblade planing (A, B, C etc.) please?  This is assuming the layout needs to be compatible with both large RTR and Kit built Locos (steam & diesel), using a track gauge of 16.2mm (00-sf); absolute minimum radius will be 750mm - but I'm aiming for nearer 900mm.

Perhaps it's a combination of both?  For example, "don't go below a B8" - but "if you're using a C then a 1:7 is ok"?

 

Perhaps it gets more complicated - does it make a difference if the turnout is curviform rather than regular, for example?  And how about slips and diamonds?

 

I realise that other factors will also have a bearing (such as side play on wheelsets) but a reasonable starting point would be a great help please.

 

Many thanks

Brian

[NFWEM57]

Hi,

 

There are many experts on this forum who will give you sage advice, I am not one of them.!  However, from my copy of the 5th edition of the British Railway Track - Design Construction and Maintenance, table 16 indicates the following ranges for bullhead rail:

• A4 to A8 (but not GWR) with a turnout radius of circa 520mm (A4) to 1,928mm (A8)
• B6 to B11 with a turnout radius of circa 1,248mm (B6) to 2,452mm (B11)
• C7 to C14 with a turnout radius of circa 1,664mm (C7) to 3,840mm (C14)
• D8 to D16
• E10 to E16 (but not GWR)
• F16 to F20 (but not GWR)
• 30ft - 13 to 20 (GWR only)

 

Tables 17 to 29 also gives details for flat bottom rail for a range of switches from A to G

 

On the other questions (side play etc) I have no idea, but the experts will hopefully advise you.

Edited December 4, 2023 by NFWEM57
Additional info on turnout radius for smaller switches

[Mark Forrest]

You may find this table of use/interest, taken from Andrew Dow's excellent book The Railway - British track since 1804.

 

On a model railway it's rare to see anything larger than a B switch and I'd imagine the vast majority of turnouts built by modellers are B6 to B8.

 

There are certain preferred combinations of switch and crossing which (if I remember correctly) give a better flow through the turnout.  Somewhere I've seen a table listing these but I'm currently unable to remember where I've seen it!

[NFWEM57]

1 hour ago, Mark Forrest said:

There are certain preferred combinations of switch and crossing which (if I remember correctly) give a better flow through the turnout.

It is where the switch radius is equal or very close to the turnout radius and they are called natural turnouts.  A8, B8, C10, D12, E16 and F20 are the ones according to the 2mm Scale Associations excellent book on Track. 

[Mark Forrest]

34 minutes ago, NFWEM57 said:

It is where the switch radius is equal or very close to the turnout radius and they are called natural turnouts.  A8, B8, C10, D12, E16 and F20 are the ones according to the 2mm Scale Associations excellent book on Track. 

Yes, natural turnouts; that's what I thinking of.  Is it A6 rather than A8 though?

[NFWEM57]

Ah, apologies, forgot to include A7, B9 and B10 but not A6 where switch radius is 482ft and turnout radius is 326 ft.

Edited December 4, 2023 by NFWEM57

[roythebus1]

Remember too the smallest radius on a turnout doesn't apply along the whole length of the turnout.

[polybear]

Hi All,

 

Many thanks for all the replies - the posts on "natural turnouts" being particularly intriguing and I'll attempt to use these wherever possible.

 

Brian