Working on planning my layout. What is the exact diameter of Lionel 072 ? Measured from what rail to what rail ? Same for 054 etc…
Here are the values I use, for the radius of the center rail of O27-profile track:
O27 12 1/2"
O34 15 3/4"
O42 20 1/4"
O54 26 3/8"
O72 35 1/4"
If you have a piece of any size, you can accurately calculate the radius of any rail by measuring the chord (the straight line distance between the ends of the rail) and using the following formula:
r = c/(2sin(a/2))
where a is the angle of the curved section (e.g., 45 degrees for O27 and O31) and c is the chord measurement. For various section angles a, the values of 2sin(a/2) are
a 2*sin(a/2)
45 .765
30 .518
22.5 .39
I believe the 072 is 72 inches in diameter measured from outer rail to outer rail. I believe this is the general standard.
When replacing track on my layout a couple years ago, I noticed that Lionel and K-Line 072 track had slightly different curvatures.
Regards,
Tim Pignatari