Turnout radius?

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

  1. rogerw

    rogerw Active Member

    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. sumpter250

    sumpter250 multiscale modelbuilder

    That sounds pretty close to me.
  3. rogerw

    rogerw Active Member

    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. Triplex

    Triplex Active Member

    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. rogerw

    rogerw Active Member

    ok triplex let me diguest this. thanks
  6. rogerw

    rogerw Active Member

  7. Torpedo

    Torpedo Member

    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. rogerw

    rogerw Active Member

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

    Torpedo Member

    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. rogerw

    rogerw Active Member

    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. Torpedo

    Torpedo Member

    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.
  12. Russ Bellinis

    Russ Bellinis Active Member

    You are correct. At the modular club I belong to in ho scale the club standards call for a minimum 36 inch radius on mainlines and minimum #6 for any turnout coming off of the mainline whether a crossover or onto a siding.
  13. rogerw

    rogerw Active Member

    Thanks all for the input. I think I will use #6 on the main

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