One of the hardest parts of the CNJ Bronx Terminal would be to make the quadruple diamond crossover. I delayed its construction as long as I could until, well, I had to build it. The diamond was not created to please the relentless railroad modeler but to cram a maximum amount of stub rails into the yard while still observing a minimum track radius. I have no idea how hard it was to build the diamond back in 1907, but I’m pretty sure that engineers who designed it were proud of their marvel when the freight yard  went into operation.

This time, working out the geometry was easy – one just has to connect the dots. The dots are the two three-way turnouts and the four straight stubs for tracks 7, 8, 9, and 10. The various plans and photos do not entirely correlate and so there’s some leeway in the detailed layout. By extending the turnouts to accommodate for the rail joiners, I already set some constraints earlier. To simplify construction, I decided to do the quadruple diamond and the four tracks in one single piece. There’s only one problem with that – the turnout on track 10 that connects to track 11 and forms the wye. I get around it by ignoring it for now. It won’t be big deal to add it later. 

Crossover Jig

I begin construction by building a simple wooden jig that would help me to place all the 8 rails in the right angles and with the correct curvature. I have the plan so I just need to flip it along the vertical axis and transfer it onto a basswood sheet using tracing paper. A French curve I’ve had since my high school days helps me to keep things aligned. The next step is to cut a gap into the wood for rail heads using the Dremel tool. Not the best method for a numerically controlled machining of a piece of wood, but good enough for my single-use jig. And I won’t be able to use the jig for the guard rails.

The jig helps me to mark the exact points where the rails intersect and to mill away the rail foot. I can’t use the jig when milling the overlaid rail head and web, but again, it helps me to identify the intersection. I get to the basic shape of the diamond in a relatively short time. Soldering the rails to those extra long PCB crossover ties from Fasttracks helps getting a robust construction.

Build and Destroy

I have noticed before with some frustration that building hand-laid turnouts is a sequence of multiple build-and-destroy cycles. This is particularly true for this diamond: The first step is to build the framework of rails. Then test if the gauges match the specs and if the overall geometry works for a single truck. In order to proceed with the next step of adding guard or wing rails, however, a lot of milling of the rails that one just soldered so nicely in place is required. 

Adding the guard/wing rails in the case of the quadruple diamond is tedious work. Ideally, each guard rail for a track should be made of one single piece. In N scale reality, it is impossible (at least for me) to always avoid fragments breaking off. Fortunately, the soldering iron is a willing instrument when fixing mishaps. After this cycle, what was once robust and looked great still looks fine but is now a bit more fragile.

The next cycle is to cut gaps into the diamonds – and that is really destructive. For a fully operational crossover under DCC, 4 pairs of intersecting rails with opposite polarity must be completely isolated. That’s cutting 16 gaps into an already fragile construct. Again, there are a few constraints to observe. First, if I maximize the  size of the intersecting segments with identical polarity and minimize the size of the segments with opposite polarity, then I won’t need frog juicers. Second, in the center of the crossover I only have PCB ties over both tracks in one direction, and I must make sure that each isolated intersection sits at least on one uncut PCB tie. A gap cut at the wrong place could structurally weaken the entire diamond crossover.

Anyway, with a careful placement of the gaps, a sharp jewelers saw, and a little bit of luck, everything works out and my crossover stays in one piece.

Fitness for DCC

To complete the electrical features of the diamond, I’ll connect the two frogs in the middle with the stock rails that have the correct polarity. In one case I have to use a small piece of wire, in the other case I can use the underside of a PCB tie. Likewise I connect each pair of tracks on the outside and inside, but not across. All stubs on the outside of the crossover will have separate feeders. The inside tracks get their power from the turnouts. Track 10 is a special case as it part of a wye and needs to be electrically separated. I decide to cut it right before the turnout to track 11 and to include the remainder of track 10 in the same power district. Its power will be provided by a dual frog juicer from Tam Valley Depot configured as an auto-reverser.

At the moment, the crossover is not connected to the outer circular track yet, so I only can test it independently from the layout. What a relief when the tests finally are positive and none of the tracks shorts.

You will notice on later photos that track 10 is slightly longer than track 9 and will reach into Lincoln Avenue. That’s different from the prototype, but it will allow me to use longer locomotives than CNJ #1000, such as CNJ #1542, an ALCO RS-3.

The last cycle of built-destroy-and-fix-it-up will be ballasting. I haven’t really decided yet on how and how much I will ballast, and I’m still hoping I will find a relatively unintrusive way that will not wreck crossovers and turnouts!