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PostPosted: Fri Sep 04, 2009 6:08 pm 
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What is the turnout radius of a #6 turnout, and how can it be calculated for each size turnout in On3 gauge?


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PostPosted: Fri Sep 04, 2009 10:39 pm 
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Joined: Sat Aug 13, 2005 10:48 am
Posts: 365
Location: East Texas - USA
The only radius that's accurate is the closure rail radius, which is not the same as the substitution radius. The closure radius represents the minimum radius through the turnout. There is a simple method and an advanced trig method. The accurate method is the trig, but the simple formula method is within +/- 0.034% accurate - which is close enough in modeling terms.

Note: NMRA tables in the RP 12.x series, use a compressed geometry with curved points, and with slightly shortened leads, thus the results are a bit different

Simple Lead and Closure Radius Calculation for Straight Turnouts: (This does not work for curved turnouts).
n= frog number
g= gauge in inches
R= radius of closure rail center line

R= 2*g*(square(n))
Length of Lead = Square Root(2*R*g)

Thus for number 6:
N=6
R=(2*36*36)
R= 2592” / 48 = 54” radius of closure

Square Root(2*2592*36)
Square Root(186,624)
Lead= 432” / 48 = 9”

Note Further: The formulas are dependent only on the frog number and the gauge. Then use the scale ratio for the modeling value. These formulas are very accurate even for full size prototype and are very close to the AREA diagrams (which use the Trig methods for greater accuracy).

I can also provide the trig formulas if the accuracy is necessary for say a CAD projection.

-ed-

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-ed mccamey-
COSLAR RR - http://www.coslar.us/
NMRA Standards and Conformance Department
PROTO & FINE Scale Coordinator
I estimate I have about 5 pounds of coupler springs somewhere in the vicinity of my workbench.


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PostPosted: Sat Sep 05, 2009 6:25 am 
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Thank you for the information. I now have a starting point.

Steve


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PostPosted: Sat Jun 14, 2014 8:54 pm 
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Joined: Fri Jun 13, 2014 8:12 pm
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I tried to use your formula to work out the radius of a #5 point and failed miserably. Well, I never was good at maths. I'm modelling a line which had minimum curve radius as small as 2 chain (33" scale) so I would like points which are no smaller a radius than that. Which one would be the best to choose? :?:


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PostPosted: Mon Jun 16, 2014 5:22 pm 
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Joined: Sat Aug 13, 2005 10:48 am
Posts: 365
Location: East Texas - USA
For On3 (36" gauge - not On30):
Frog_____Lead_____Closure Radius
4.75____7.125"____33.844"
5______7.5"_______37.5"
5.5_____8.25"_____45.375"
6_______9"_______54"

I have a nice spreadsheet that allows 'what if' calculations using the formulas shown in the thread above.
-ed-

_________________
-ed mccamey-
COSLAR RR - http://www.coslar.us/
NMRA Standards and Conformance Department
PROTO & FINE Scale Coordinator
I estimate I have about 5 pounds of coupler springs somewhere in the vicinity of my workbench.


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