Dual Gauge Junctions

If you have made a dual gauge railway junction, you will know that both the construction process and the final product are significantly more complex than those for a single gauge junction. This is true even if you call the junction a turnout, a switch, a splitter, a point, a set of points, or something else. Furthermore, operation can give difficulties. I note that the WikipediA entry on this topic contains the sentence "The train must move through a dual gauge switch very slowly."

I have seen operational problems on others' G0/G1/G3 dual gauge junctions, and I have experienced them myself. I set myself an objective of avoiding such things on the portable railway; and I think that I have been successful. It has taken a lot of work.

This problem necessarily occurs in a dual gauge junction at the location where the narrow and broad gauge rails intersect each other. The image below is of a G1/G3 junction from my defunct garden railway; and the problem intersection can be seen in the middle of the second rail from the bottom. The problem occurs with the broad gauge rail as it goes left to right and up, and with the narrow gauge rail as it goes left to right and down. In both cases, the gap between the rails is huge and a lot of, probably most, wheels will drop into the gap because they are too small in diameter, and their tread not wide enough, to bridge it. So the train goes bumpity-bump. One solution is to support the wheel on the outer diameter of its flange, which can reduce, but not eliminate, the bumpity-bump.

Moving point frogs (aka swingnoses) are used on junctions for high speed operation, and in some other applications. In all these cases, a shallow angle between two rails causes a long gap, just as in the portable railway rail-intersection problem area. So, seeing the similarities, I implemented moving points, as seen in the image below, which is of a G0/G1 junction of the portable railway. The junction layout can be compared with that in the previous image. It can be seen that the problem rail gaps are closed completely by the moving points. Also evident is another advantage of moving points: check rails are not necessary.

However, the problem with moving points is that they have to be moved; the actuation rods, including a Carden shaft coupling to deal with the curved track, can be seen in the image.

Since it is now necessary to have rods to move these auxiliary points in synchrony with the main point blades, it is a small conceptual step to go the whole way and have moving point frogs throughout the junction. In these images the main points are not in view, but the other four can be seen, together with the actuation rods. The points have been switched between the two images.

All four Baseline-Plus mainline junctions are made this way; which means that they are quite complex relative to a junction with a simple ground throw next to the main point rails. However, these portable railway junctions are smooth for all trains to run through, and they satisfy my glitch free objective. I note that, since check rails are not necessary, moving point frog junctions are very tolerant of wheels made to standard, fine-scale, or even out-of-spec, dimensions.

The flag shown below is optional by being detachable; it is mounted on the junction ground throw and it flops over the track not in use. Putting the ground throw in the crotch of the junction keeps the envelope of the module completely within the general outline parameters for modules. In other words, there is nothing sticking out to be damaged.