For railway tracks, why do we need to put a scotch block at the points?

Answer 1

I won't claim this is my own explanation... Wikipedia has much better wording than what I could come up with!

"To clip and scotch a set of railway points (Amer. a switch) uses two pieces of equipment to temporarily lock a set of points into a particular position. The point clip clamps the end of a moving rail (the switch rail) of a set of points to its associated stock rail, and the scotch is a timber wedge used to ensure that the other moving rail is kept away from its associated stock rail. In this way the points are fixed in either the 'straight through' or 'divert' positions and cannot be moved by the usual setting mechanisms. For infrequently used points, this guards against mechanical failure of the points leaving them in a condition to derail trains. The 'clip and scotch' method can also be used to positively deny access to the turnout or mainline.

A 'scotch block' is not used, as this is a different piece of equipment clamped to a rail used to ensure that stationary railway vehicles do not move, with much the same function as chocks used to keep aircraft stationary."

Answer 2

Lost me there, I looked in Wikipedia and all I saw for scottch block is a chock for placing under the wheels of a train car.
Nothing about the points by which I imagine you mean switch points?
Blocking the wheels, is an effective way to hold a car for a brief period of time without climbing on the car and setting a handbrake when you only need it to stay put for a few minutes, perhpas as part of a switching movement.
Also it is required in some cercumstances to block the wheels of a car, if the handbrake or airbrakes fail or are released for whatever reason (vandalism?) that car will not roll out over the block until it is removed. One more layer of protection.
I hope this helps, I wasnt really sure what a scotch block was, I have heard lots fo terms on the RR but never that one.

added later, ok, with scotch blocks you ARE referring to a device to lock the swhtch points. Here we call it "spiking" the switch, there is a square hole in a switch plate as part of the switch mechanism that track workers can drive a spike in and lock the points.
Imagine you have a peice of track with a rail missing, or a disabled peice of equipment that you dont want moved for any reason. What better way of making sure NO ONE will get into that peice of track than to block the switch points so that it cant be moved until the block (or spike) is removed.

Answer 3

To stop the points moving for some reason.