Switch Rebuild: Part 2

Two steps back. My bold prediction on how I'd approach switch rebuilding has had to be revised—and no, I'm not disappointed. And while I won't be using the points I'd made previously, it was not a wasted exercise by any means. The basic concept of the new design is still the same, but the specifics are quite different. Allow me to go into excruciating detail...

I was on the verge of soldering the two point parts together when it occurred to me that I was looking at a potential shorting issue. With the points electrically tied together, it meant that, being the same polarity, the backs of the wheels facing the point rail not in use would be of opposite polarity, and given the high variability in flange width, I foresaw an unfortunate situation (below). So, the points could not be made from a single piece of metal.



This was not the end of the earth; it simply required a bit more thought. If nothing else, this simplified the mechanism from the standpoint that the wiper parts to feed current to the points would go away (they had to anyway, because using PC board as a cover plate on the bottom, as I'd intended to do, was not an option owing to its thickness). But how to reliably power the point rails?



The answer was provided by Eishindo. The original point design (above), which uses magnets to hold the points in position, also appears to use the magnets to improve electrical contact with the stock rail—even though the points are uselessly short to provide much of an electrical performance advantage. They'd even gone to the trouble of gold-plating the points, so it seemed as though it might be a good conceptual starting point.

Introducing my new point design, version 2.0 (below). It consists of two pieces of thin gold-plated sheet steel, .040-inch-high, with small tabs embedded in a cast-on plastic fulcrum (similar to the way the existing points are manufactured—at right). The metal is thicker than the original parts for more rigidity. The extensions on the ends provide additional surface area for contact with the stock rail and existing magnet assembly for the best possible electrical conductivity, as well as to hold the points in position (doing away with the need for a mechanical indexing mechanism underneath). And with the points being isolated, the point rail not in use is electrically dead, eliminating the possibility of shorts.



The flat top of the fulcrum part may vary in length from the way it's drawn depending on how much of the point rails need to be embedded in order to maintain sufficient rigidity; it could run nearly the full length of the point assembly, although I think the ends of the point parts should have a bit of flexibility in order to provide the best possible mechanical contact with the stock rail and frog point.

The fulcrum may be secured to the base in a number of ways. One thought is simply a screw and washer; another might be to cast small triangular tabs on either side of a split fulcrum so that the point assembly simply snaps into the hole. The specific method employed is unimportant, and more dependent on manufacturing costs: the former approach is more labor-intensive to assemble, while the latter potentially changes the fulcrum mold from two parts to three.

Not shown in the illustration is the new throwbar, which simply has a block that extends up in between the point rails and presses on the inside surfaces to move them. This may or may not require lengthening the extension tabs at the ends of the points for more rigidity and to lower the throwbar block. The throwbar may also need to be relocated from its current position in order to give it more mechanical advantage and reduce its travel.

These details will be ironed out as I begin experimenting. Stay tuned for Part 3.