About Spring Switches
Switches come in all shapes and sizes. Switches are designed to allow trains to choose multiple paths—but sometimes you don't need as many options.
Real railroads have used spring switches for more than 100 years to make repetitive operations easier and faster. A spring switch allows trains to pass through the points from either diverging direction when approaching the switch from the diverging routes. (This would be called a "trailing point switch.")
As the train passes through the switch against the points, the spring compresses allowing the train to pass without derailing and then snapping shut again as each wheel clears. This avoids having to stop to open and close the switch to set the route for the train.
When a train approaches the switch from the other direction (facing point), the spring tension keeps the track aligned for the normal route. A switch stand or motor is usually placed here as well allowing the switch to be thrown for the diverging route in the odd situation.
Spring Switches in Model Trains
Model railroads also use spring switches as a special type of switch or turnout that has its points sprung to return to a normal position. The weight of the train and the flange of the wheels push the points out of the way while passing through. This allows a train to pass through either diverging route from the front end, but facing the switch; the train will only go the normal route.
Spring switches are used where trains normally pass through the reverse leg of the switch in the trailing-point direction but the normal route when facing. Passing sidings, runarounds and switchbacks are common uses on the prototype. A spring switch always set to normalize to the left at each end of a siding, for example, will allow two trains to pass in opposite directions without re-aligning the track safely.
Most prototype spring switches also have provisions to manually line the route in the event of an abnormal move. Also, trains are normally prohibited from making a reverse move before passing completely through such a switch. Such a move would result in the front of the train taking the opposite route.
Spring switches are easy to make on model railroads with a short length of piano wire. Since model trains are much lighter than the prototype, the tension should be kept to a minimum to prevent pushing trains off of the track.
Making a Spring Switch for a Model Train
To create the spring, use a stretch of stiff wire (piano wire works well). Cut the wire to a length of about three inches. The exact length is not critical.
Make a 90 degree bend about 3/8" from one end of the wire. Insert this end into the cork roadbed or benchwork on the outside of the rails, behind the points. A stiff and sturdy roadbed base is beneficial to this operation.
Insert the other end of the wire into the throw bar.
Now create a fulcrum out of a second short piece of piano wire or even a track nail. The placement of the fulcrum will determine which direction is "normal" on the switch. Place it on the inside or outside of the spring wire.
You can adjust the tension of the spring by moving the wire forward or backward. The closer you place the fulcrum to the throw bar, the more tension will be applied. Given the light weight of our cars, you'll want to keep the tension as low as possible to close the points without requiring excessive force to open them. Pilot wheels on steam locomotives tend to have the most trouble and make a good test car.
Once you're satisfied with the operations, you can ballast the switch as you would normally. Spring the switch a few times as the glue dries to keep it working smoothly. The wire, especially if painted black, will be barely noticeable once completed.