Thanks to all for the input-- expansion allowance needed, rails not with equal diameter (single rail bender vs. dual type)-- I appreciate the help.
The bender used was a single rail type - must have been old.
Wendell
I believe another variable may be if its a full circle or oval verses a loop that may be L shaped. I believe that a circle would find the radius it wants to be and stay there, but the odd shapes would not have the even tension to hold them selves in shape the same way.
Could be Randy, but I also have 1 curve that is almost a loop, but not quite. The ends do not connect, they just run alongside each other for a brief distance. And I have another curve that is over 90 degrees. And one that is less then 90. Those curves haven’t tried to straighten themselves out neither. If Wendell is indeed having the issue he says he is having, it would be interesting to know why. But, we probably will never know for sure.
I did have a small section that narrowed its gauge, and I do not know why. But it appeared that the outside rail came in, so it increased its bend, not decreased its bend. I blamed it on the deer that like to frequent my yard.
After I laid the track, I did read somewhere that rails will eventually try and straighten back out. I decided that I would deal with that when and if it happened. But in my experience, that warning appears to have been one of those myths that is just passed along.
If you think about it, if metal is bent, it will hold its shape. If metal did have a tendency to unbend, then all them old classic cars would be flat sheets of sheet metal by now. And half of the coat hangers in my closet would be straight metal rods. But like Greg said, during the initial bending, the rails will spring back a bit. So we set our benders to bend a bit more then we want, just so long as the final result is what we want. After that, the metal should be stable.