Rick, I found our problem!
We're thinking with our old knowledge of good old Lionel tubular track in regards to diameters, etc...
Ross track measure center rail to center rail, while Lionel measure outside tie to outside tie.
This is why the figure 8 doesn't work. The Ross track 31" curve take up more space than the Lionel.
I have attached a screen shot of RM Pro. On the left is a half circle of Ross O-31, on the right is Lionel O-31.
Using the measuring tool, the Lionel comes out to overall outside diameter of 31".
The Ross circle measures about 33.15 " outside diameter, and comes in right at 31" center rail to center rail. You can visualize this as I tried to line up the outside of the Lionel with the center of the Ross.
I learned something new today ![](https://ogrforum.com/static/images/graemlins/icon_smile.gif)
Based on this and what I discovered about Ross track diameters, Rail Modeller Pro is correct in this case.![rmpro rmpro](https://ogrforum.com/fileSendAction/fcType/0/fcOid/50704664824380135/filePointer/50704664826573460/fodoid/50704664826573456/imageType/MEDIUM/inlineImage/true/rmpro.png)