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Hi all

So I'm starting to build my first layout. It measures 8x16. I had originally intended to make my outer loop O84 lionel fastrack, but instead have decided to go with atlas. My question is how does atlas measure their track? Center rail to center rail or outer rail to outer rail? In other words, would I be able to go with O90, or would I have to go with O81 for my outer loop?

 

Thanks

Last edited by Hebanator
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Depends on how close you like to run trains from the edge of the table. From the middle of the center rail to the outer edge of the ties is about 1 1/8”.  From the middle of the center rail to the outer edge of a switch machine is about 2 1/2”.  So 96” - (O90 + 2 x 1 1/8”) = 3 1/4”.  Divide by 2 gives about 1 1/2” from the edge of the table to outer ties.  If there is a switch machine on the outer edge it is about 1/2” from the edge of the table.  You would have to decide if that is running trains too close to the edge.  You don’t have to use all the same radius curves.  For example, an outer half circle of O90, O90, O81, O81, O81, O81, O90, O90 gives you about an O85 circle.  An inner half circle of O81, O81, O72, O72, O72, O72, O81, O81 is about O76.  The two circles are concentric with the Atlas 4 1/2” spacing.  You can use other combinations of curve radii and as long as the curve section on the inner track is one size smaller (9” diameter) than the one on the outside track, the 4 1/2 track spacing is maintained.  For the equipment I run, 4 1/2” spacing on parallel curved tracks is too close.  I run all O72 on the inner track and the O81 with the O90 easements on the outer loop.  That gives a close approximation to Lionel O84 and O72.

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