Turnout radius's

[Anonymous]

Hey Guys..
I'd like to know what size tunout to use on what size curves.. # 4 turnout ?? # 6 turnout ?? what to use on straight run and what to use on curves? is #4 & #6 the only sizes needed?? Another question from a beginner,, Thanks guys..

[Anonymous]

First, I use H O Scale so that is what I can help you with. With 18" min. (sharp) radius on the mainline, No. 4 turnouts are recommended unless you are constructing a crossover, where you would want to use a pair of No. 6 turnouts. The Atlas Customline #4 turnout is a No 4-1/2 in reality (according to John Armstrong). A No. 4-1/2 is certainly OK for mainlines up to 22 in. rad. curves. From 24 to 30 inch curves, you should consider turnouts larger than No. 4. I have occasionally read about No. 5 turnouts but I haven't bought any yet. At 30" radius, I would try and stick to No. 6 or larger turnouts and I would use No. 8 or larger for crossovers. The reason you want to use larger frog numbers on crossovers is because they comprise a reverse curve, the most troublesome alignment. You may still want to use No. 4 turnouts on freight yard ladders, branch line trackage and freight spurs. I don't recommend using the Atlas Snap Switch because the radius of this switch is quite tight. Stick with the Atlas Customline No. 4 or larger.

The equivalent radius of various turnouts are:
No. 4 29 in. rad.
No. 4-1/2 36 in. rad.
No. 5 44 in. rad.
No. 6 56 in. rad.
No. 8 110 in. rad.

The radius of the closure rail is slightly less.

Good Luck - Ed

[thirdrail1]

There are no "equivalent radii" for turnouts. The number is the ratio of the angle of divergence of the two STRAIGHT segments through the frog. That is, the rails diverge 1 foot for every 6 feet of rail length in a Number 6 turnout. Some turnouts, such as the Atlas Snap-Track type, do have curved diverging rails, but numbered turnouts have no radius at all.

[Anonymous]

Have you read NMRA RP 12.3 or p.46 of John Armstrong's book, "Track Planning for Realistic Operation"?

Ed