Discussion in 'Track Planning' started by rogerw, Apr 22, 2007.

1. ### rogerwActive Member

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I did a search on this and found out according to nmra that #4 is about a 18", #6 about a 22". Is a # 8 about a 26 " radius? I would make sense but want to be sure.
2. ### sumpter250multiscale modelbuilder

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That sounds pretty close to me.
3. ### rogerwActive Member

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Thanks sumpter the page I found at the nmra site only used the #4,#6 on the page when they discussed turnout radius . just making sure.
4. ### TriplexActive Member

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Assuming you're talking HO, http://www.nmra.org/standards/rp12_3.html says that a #4 is 15" radius, a #5 is 26", a #6 is 43", a #7 is 49" and a #8 is 67". These numbers are the actual minimum radius in the turnout; straight-frog turnouts cannot be fitted into continuous curves of matching radii.
5. ### rogerwActive Member

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ok triplex let me diguest this. thanks

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7. ### TorpedoMember

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I found these in John Armstrong's "Track Planning For Realistic Operation" for HO.

#4 15" RCR, 29" SR

#6 43" RCR, 56" SR

#8 67" RCR, 110" SR

Where RCR is the radius of the closure rail (the sharpest radius in the turnout), and SR is the substitution radius for fitting the turnout into a curve.

Hope this helps.
8. ### rogerwActive Member

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I am talking in HO but those numbers dont make sense to me.
9. ### TorpedoMember

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The Armstrong book is considered the bible of track planning. He goes into considerable detail in this area (too much for me to repeat verbatim), but these are the numbers he came up with after years of track planning experience.

A lot of people recommend "Track Planning For Realistic Operation" for anyone designing a layout. Personally, I think it is the single most valuable MRR publication out there, regardless of price.
10. ### rogerwActive Member

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I guess what im wondering then if im using a 30" radius on my main line and I put some #6 turnouts for branches it wont lower my min. radius of 30 " through the curved part of turnout?
11. ### TorpedoMember

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Not according to Armstrong. He says that you can even use a #4.5 with up to 30" radius curves.

#4.5 22" RCR, 36" SR

#5 26" RCR, 44" SR

Basically, he argues that #6 and #8 turnouts are space wasters on model railroads, especially with radii of 24" or less. Other than the comment regarding #4.5 turnouts and 30" radius, he really doesn't address broad curves (his definition of 30" radius and greater in HO) directly.

His most basic point seems to be this: The radius of the closure rail (RCR) will affect how "stiff" eqipment like steam locos will negotiate the turnout, and the substitution radius (SR) will affect the train as a whole.

BTW, he argues for laying your own track and building curved turnouts when needed. He diagrams how that saves space.

He does argue for higher numbered turnouts in reverse (S) curves for other reasons, which he discusses at length in another section of the book.

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