Clark and interested others of the list, I use data scaled down from AREA drawings as well as data from a wonderful little book entitled "Simplified Curve and Switch Work" by W. F. Rench, formerly Supervisor on the Pennsylvania Railroad. This handbook, printed in 1928, provided "Valuable and necessary information for the Supervisor, Roadmaster and Foreman, and for College instruction".
Because of the non-scale dimensions of wheels and wheel set back-to-back measurements used in nearly all equipment running on gauge 1 track, compromises are required in building up a good working turnout. This combined with the desire of some end users to get as big a loco as possible through the smallest turnout make it a challenge indeed. The main limits are the fixed wheel base of the loco and how much side play the drivers have combined with the amount of lateral movement available in the pilot and trailing trucks or wheels. Yes, I recall storys of folks taking both pilot and trailing wheels off to get around less than recommended radius curves. In a real turnout the point rails that allow route change are available in about 4 different angles, called a "switch angle" (not to be confused with the frog angle). These vary from a little over 2 degrees and 10 foot in length and used on a #4 or #5 frog turnout to less than 1 degree and 30 feet in length as used on #18 thru #24 frog turnout. This is the first "bump" as Clark mentioned. This is followed by the closure rail radius and on to the second "bump" as the closure curve goes into the pure angle of the frog for the length of the frog, this is actually the point that the radius starts to unwind a little. After the frog, the rails should go gently on their way straight for a distance or, if not, be allowed to a very gently curve which might be the third bump if you are not careful. Full size railways used curved turnouts with curved point rails to ease the transition and lessen the bump.So it does not hurt at all to bend the point rails to lessen the bump on our model turnouts as well. We can also build with curved frogs which also make for smoother running. By the way, that # 24 turnout I mentioned above has a closure rail radius of 5600 feet. Yep over a mile radius, let's see using 1:32 scale that would be a 175 foot actual radius curve on a turnout about 7 feet long! Gary Broeder LCRwys.
