Update, minor problem in "standards of measurement"-makes this even worse!!!
The diameter of O27 track is measured from the outside edge of the tie on both sides. When you measure center to center, the way other scales do, it’s actually about 25 inches in diameter.
It’s not hard to find someone who says their O27 track is a bit wider than 27 inches measured edge to edge. There was some variance over the years and between manufacturers.
Again, that implies that a 31 Inch diameter O-31 track probably won't even land on your existing elevated structure.
@My Lionel posted:This 027 circle is attached on elevated columns, & without tearing apart my train table, can I use a different gauge track that will make the same circle.
