# How to determine inner radius of a (#5) curved turnout ?

Discussion in 'Track Planning' started by ulf999, Jan 25, 2008.

1. ### ulf999Member

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Hi all!

I'm planning on using a few #5 curved turnouts (fasttrack TwistTies) with an outer radius of about 40" (100cm).
What I can't figure out is what the inner radius would be?

There just has to be a math formula out there...?
Google couldn't help me, anyone here?

/Ulf
2. ### SquidbaitRecovering ALCO-holic

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If you have the Fast Tracks jig for the turnout, it should tell you what the radius of the inner curve is.

Based on the numbers for the #6 curved jigs, I'd guess it's in the 26" - 28" range.
3. ### stdguageMember

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Scale track, as opposed to toy snap track, does not tyically have a radius. Two straight lengths of track meet at a specified angle. Modelers will ususally begin a transition and then a fixed radius a few inches after the frog, but the radius is of your own choosing. The smaller the turnout frog number the larger the angle.
4. ### stdguageMember

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Also, there are curved turnouts. They usually still use the same frog, begin the radius within the frag angle itself.
5. ### ulf999Member

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I see. Then I now have the choice of either curving the frog at desired radius
or having a 'regular' frog and from its angle continue out to follow a curve with my choice. How hard can it be
6. ### stdguageMember

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Yes. Remember that you also need to make a transition from straight to your curve radius. For handlaid track, you might want to also check out the Yahoo group. More information and always good advice.
7. ### pgandwActive Member

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You are not going to be happy with the answer. The inner radius of a #5 curved turnout with a 40" outer radius is going to be down in the low 20s or even teens.

Walters figures for their curved turnouts are very deceiving. The inner radius for those who have actually measured it is much less than advertised, often by 4"-6". A straight frog, curved turnout with decent radii on both legs is going to be very long.

As an experiment, lay out 2 curves of the intended radii starting at the same point. See just how long it takes to gain 1.5" of separation between the 2 centerlines.

A straight frog makes matters worse, because the curved portions of the turnout have to be sharper to make up for that straight frog, yet still keep the intended substitution radius.

Typically, curved turnouts with straight frogs need frog numbers 2-3 numbers higher than used on straight turnouts.

There is a useful Excel turnout calculator available here (da Trains! - Railroad Data) which can answer your questions. Look at the curved turnout sheet.

hope this helps

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