That NMRA table contains data on the equivalent curves and the actual curvature of the closure rail - but only for turnouts built to the dimensions in the table! I don't believe that any manufacturer has ever hit them exactly.
The straight rails on the diverging side can be cut back to just short of the guard rail ends, reducing the mandatory straight section through the frog to only a few scale feet. Best way is to cut the plastic spikes off the ties and bend the rails, then modify the ties for appearance.
Of course, the fall-back position is to build your own specialwork. It is NOT rocket science - all you need is some good track gauges (including the NMRA gauge), a big file and a soldering tool of appropriate capacity. Home-builts can be built to specific radii (curved points and curved through the frog,) or to whatever frog number the specific situation calls for. Once you have learned the necessary skills, the result is beautiful, dependable, smooth-flowing trackwork - and who cares what the frog numbers actually are?
Chuck (modeling Central Japan in September, 1964 - with hand-laid turnouts)
You might find NMRA's page on turnouts helpful http://www.nmra.org/standards/rp12_3.html
A #4 is 14d 15', #6 is 9d 32'. Of course actual manufacturers may use round off or use something different.
Except for curved turnouts such as Atlas snap switches, turnouts contain straight track so no curve will look smooth.
Enjoy
Paul
Andy Sperandeo MODEL RAILROADER Magazine
Depends. British style turnouts, like Peco (the older ones) are curves throughout the diverging route. N. American ones are straight for some distance, but then anything goes.
Remember that one should not revert to parallel to the through route of the turnout, as one would in a yard, too quickly or you get a horrible S-curve.
I can't remember off-hand what the curvature radius works out to be for a curved diverging route on a #6, but it would be at least 26", and probably more like 30". Edit- the radius for a #6 is between 40-45". For a North American style, the "substitution" radius, since it is straight for most of it, is much more.
A #4 turnout is often used by modelers in a yard, although it restricts the locomotive and rolling stock somewhat. For example, you are not going to get a BLI Texas-Type 2-10-4 through a #4. Its minimum radius is between 22" and 24", while the #4 is around 19"...that much too tight.
A #4.5 or a #5 turnout, is going to be the best match for 22" curves.
And if I follow you on your question, yes, I think a 22" curve would look odd with a #4, but you would have to try it and see for yourself.
I could use some help with turnout terminology. As far as I understand, a #4 peels away at an angle of about 12.5-deg and a #6 peels away at about 10-deg. But is the end of the track that's turning out straight or curved? Certainly as you transition away from the main line, there's a curve involved, but what's this radius? If I attach a 22" curve to the turnout, will the track appear curved as it peels away from the main line, then straight for a little bit, then go into this 22" curve? (Therefore "wiggling") Would this look odd?
I'm trying to design a layout w/ a 22" minimum radius. Given that constraint, is a #4 compatible?
Thanks.