Single point turnout geometry

The two turnouts I’m using on the Coy Paper layout are both single point “trolley” turnouts. That’s what was in place when Pinsly installed the two car runaround in West Claremont to make switching Coy Paper easier and certainly they were, one more thing, that made this so appealing as a model railway for me.

As the above image from the Richard Orr catalogue illustrates, the single point is on the inside of the turnout and the point’s job is to catch the back of the wheel flange and guide the wheels into the diverging route.

In my model I estimated the end of the fixed point by the width of a flangeway, like I’d use elsewhere, found marked on the side of my NMRA gauge. I filed this fixed point down to a fine tapered edge so a truck glides across this space.

A real turnout is a series of tangents, not curved rail, but in a model I’m not that bothered with a rail that’s slightly curved. In these single point turnouts I think that ensuring the rails are tangents and parallel (point is parallel to the stock rail) becomes more crucial.

When building a “regular” turnout we never really think there’s much concern on how long the points actually are. If we’re building an accurate model of the real thing we simply measure the real thing and divide by our scale factor. In a purely model form, if it looks right it’s probably darn well close enough. When I built these turnouts, as shown in the photos, I have left the point itself fixed to the rail because I’m not sure if I’m going to hinge it or not. As well, as mentioned, the idea is that the point is supposed to guide the back of the wheel flange into the diverging route. When I built this turnout I set it up so that point was at least as long as the truck’s wheelbase that would be navigating through it. This made sense at the time.

As luck would have it, the first turnout (the one starring in these turnouts) is the one on the right in the track plan. In a typical operating session it’s the one that isn’t under a lot of pressure to work flawlessly every time. When I built the second turnout, the one that connects to Coy, I made the point too short and that helped me appreciate how important that point’s length is in these turnouts. I can easily replace the point with a longer one but am writing this to acknowledge that lesson learned.



Categories: Coy Paper (HO) model railway, handlaid track

Tags: , , , ,

2 replies

  1. Actually, in coarse HO scale, you often can’t model the point length accurately because it doesn’t leave enough space for the flanges, and the narrow back to back binds on the wide heel of the point. I suspect you’re benefiting here slightly because you actually want the back of the wheel to foul with the back of the point.

    • Yes. I agree.

      In coarse HO, on a longer turnout, I’d always be trying to tighten things up as much as possible at the frog because the coarse standard seems to create a void between the closure tails and the crossing nose. On these turnouts, the prototype handed me an opportunity to build much smaller turnouts (I think these two are #5’s) so that angle at the frog is so that the traditional wheel drop won’t happen there but I do notice the same happens when the wheel carries from the stock to closure on the side of the turnout that doesn’t have a point – not so much on the rightmost turnout but more so on the leftmost. Last night I redid the point and closure rail on that “left” turnout which corrected the issue with catching the back of the wheel and guiding it properly but that success only further highlighted the issue on the adjacent rail. Over my first coffee this morning I’m studying the turnout to see how I can take the front of it apart to rebuild it in the hope of refining out both problems.

      It’s “funny” how these things work out. The first turnout is very smooth. I can’t force it to fail no matter how I push that test truck through it. The second seems to have collected all the issues. As model railroader’s luck dictates it’s this sscond one that is the backbone of every operating session.

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