Reply to "Defined flex track arc in RR-Track"

You have to do a little math. Keep in mind that you'll still be doing some cutting of the rail ends on the center and inside running rails.

1. Atlas flex is 40" long, so your half circle's outside rail will have a length of 160"
2. Divide the 160 by PI (3.1415926) That will give you the curve's radius (50.93)
3. Select "Custom Radius Curve" as your track section.
4. Set your arc to 45 degrees.
5. Set your radius to the number you got in step #2 and you should be good.

Note I said radius above. O gauge 3-rail track is referred to by its diameter which is twice the radius, so your curve above will be O-101.86