Track switch machine controls or why can’t I find a 40+ year old switch?
Waaaay back in about 1979 there was a group of us who frequented an electronics store in Seattle called Radar Electronics. Someone found some neat toggle type switches that were used in audio applications, and thought they might work for controlling track turnouts. A variety of designs emerged, but most seemed too complicated for me, so I set about to come up with a very basic one that would be simple, reliable, and easy to assemble. I am in favour of having a small slot under the turnout throw bar and a stiff spring wire that comes up from below and moves side to side with just enough tension to keep the point firmly to one stock rail or the other. Other ideas used bell cranks, rotating bits, etc, but they seemed more than what was required to simply move the points from side to side. If you wanted a rotating switch stand that was a different issue, something that I have chosen to avoid.
Back to the toggle switches. They may have been sold individually for a price that is long forgotten, but the best deal was a box of 200 for $50.00, or 25 cents a piece, what a bargain! Needless to say everyone bought a box.
My simple design involves a piece of 0.025” or 0.030” piano wire plus two mounting brackets made from aluminum angle stock. The electrical part of the switches was basically a slide switch, and I have never liked them for reliability, plus they are not designed to handle much current, being mainly for audio applications. I decided on snap-action micro switches which are designed for higher current and are extremely reliable because of their snap-action internal design. One (or two, I’ll get to that part shortly) were simply screwed to the bottom of the subroadbed plywood and actuated by the lever on the audio switch. Short wires lead up to the track stock rails and the frog so that every inch of rail is live.
One thing worth mentioning is that it looks from the photos that I have soldered the spring wire to the handle of the toggle switch. This is true, but I don’t trust a simple solder connection so I put a 90 degree bend in the end of the spring wire, put it through a hole in the end of the handle, and then wrap regular bare hook-up wire around it tightly and then solder it all together. This encases the end of the spring wire in a layer of soft wire that is all soldered together. I have never had one come loose.
As for the need for two switches, this arises with the older Shinohara style turnouts that have a solid metal bar connecting the points to each other and then to the frog. This resulted in a large portion of the turnout that was powered as a single frog from the switch machine below. Now those points act as a switch when they touch their adjacent stock rail, and we have the micro switch below deck also trying to switch the frog. Because the micro switch transitions very quickly and no dead space, one or the other position ends up with a short circuit as the turnout points and the micro switch are both supplying power and get out of phase. The simple solution is to install two micro switches in such a way that as the points move from one side to the other the first micro switch opens, usually before the point has left the stock rail, and then the other micro switch closes sometime later as the point arrives at the other stock rail. This design has worked flawlessly on many Shinohara turnouts for many years. All of them are considered to be “not DCC friendly” but I have never had any problems using them with DCC and all sorts of rolling stock. It is all in how you handle powering the frog. In fact, that solid throw bar that is seen by some to be a source of grief, helps with the power supply to the points and frog. The switch frame below can be wired to the micro switches so that the spring wire driving the points provides a third route to power the points and frog. All it takes is the “break before make” design accomplished with two micro switches.
For other turnout designs that connect each point rail to its adjacent stock rail and only the actual frog needs to be reversed, one SPDT micro switch will suffice as it will route either stock rail to the frog as appropriate. This design has also been working flawlessly for many years with PECO and other turnouts.
These assemblies are operated with yet another simple design utilizing RC airplane parts, namely their 2-56 threaded clevises, threaded rod, and 1/4” wooden dowels. All of this idea was borrowed from Jim Petro down in Reno NV. Thanks Jim! I have used a few of the nylon control surface push-rods as well for hard to reach places that can’t have a direct straight dowel.
I also stole Jim’s idea for using PVC pipe end caps as recessed holders for the dowels so that the face of the fascia can remain clear and smooth. I even managed to track down and order several boxes of the exact make of PVC caps that he used because they were so much nicer than the ones locally available.
All of this is shown in the accompanying photos.
Now, the part about trying to find new switches? Well, I decided to see if there was anything available on the market today that would work in a similar manner to my 40 year old switches. Their application in audio amplifiers is long gone, with everything being computer controlled. I managed to source a bunch of sort-of similar switches directly from China after searching through hundreds of pictures of different models. I made a small mock-up to try them out and I believe that they will work just fine, along with the micro switches, but I have not installed any yet as I am still working on my stash from 40 years ago. Time will tell.
As for sourcing the micro switches, these used to be available from the many electronic equipment suppliers, many selling surplus stock, but all of them have now closed. There used to be a whole bunch in the San Francisco Bay area, but one by one they all closed. I was fortunate to secure quite a number on various trips down there, so again I should be well stocked for a quite a while. I am sure that suitable micro switches are also available online, probably from China.