In general, rail is quite flexible horizontally, much less so vertically. Quite often, when building track, if a curve is necessary, bolting two or more rails together and using the loose end as a lever allows a smooth curve to be effected. As the curve continues, additional rails are bolted on and swung. A rail bender is only needed, as mentioned above, to bend the curved stock rail in a switch, to bend the wings of guard rails and similar jobs. Using a bender requires a certain amount of finesse, as it is possible to kink, tear or even break the rail if you are overzealous.