how are cross-over bends of rails made?

Answer 1

I'm not sure of the question, since some terms have been interchanged.

A cross-over is a track connection between two adjacent tracks, incorporating a switch on one rail and a switch on the opposite rail.

Your choice of the word "bending" is interesting, since a slang term for operating a switch is called "bending the rail". The way a switch operates, there is a movable portion called the "switch points". There is a mechanical connection between the "switch stand", the device that operates the points, and the points themselves, which are tied together by a steel rod. Switches usually have only 2 positions, "normal" and "reverse".

Starting in the normal position, the points, which taper as they near the tip, would be in a configuration where one side makes contact with the rail, creating a gap on the opposite side for the "flange way." The flanges are raised portions of the inside of the wheels which extend below the height of the rail to guide the equipment.

When reversing the switch, the switch stand is operated moving the points to the opposite side, where the point now makes contact where there was a gap, while a gap is now created on the other side.

Further down the switch will be found the "frog". This is a heavy component with "grooves" molded into it to allow the flanges to cross over the rail when moving from one track to the other. As insurance against a flange going the wrong way over the frog, there is a short piece of rail on the inside of the "stock rail" (just another name for the outside rails of the switch) that doesn't appear to be connected to anything. It is there to keep the flanges from "picking the point" of the frog, creating a derailment.

There are moveable point frogs, however, and should not be confused with the switch points.

The switch stands themselves come in a variety as well. There is the familiar "high stand", "ground throw", "variable", "submarine", "pneumatic", "spring", "controlled" and "dual control". But these are another question.

Answer 2

Are you referring to switches? In that case a "frog" provides the actual cross over. The moving parts are simply strips of rail - despite being steel its quite flexible. Hence the term "bending the iron" for throwing a switch.