Over a few weeks in the Spring of 1997, several of us in the MS-Rail group began giving some thought to the concept of reversible NTRAK corners. By reversible, we mean the same module can be used as either an inside or an outside corner.
The whole discussion started when Hans Spiller spent some time with Matt Schaefer of the Northern VA NTRAK club. Matt had written an article on through yards for the NTRAK Newsletter which had inspired the design that eventually led to Hans' yard. When Matt heard that someone had actually built the yard, he was interested in talking to the builder and so Hans and he got together. During the course of the discussion that followed, Matt made mention of a design he'd been working on for a reversible corner. Hans mentioned this to the rest of us and that sparked a discussion which led to the plans you see on this page.
In presenting these plans, I'm not advocating any one design over another. They each have merits. I'm merely presenting them as interesting module designs.
Matt's original design is basically a standard 3' outside corner that can be used in reverse.
When used as an inside corner, it becomes a 4' 1" corner. (If NTRAK had thought to place the
second main line at 18" from the skyboard instead of 18 1/2", then there wouldn't be that
extra 1" of slop to deal with. It's unfortunate but on a larger layout
the modules are flexible enough that it really isn't a problem.)
The truly clever thing about Matt's module design is the way the two extra pieces are moveable to
keep the whole module in a compact shape while always providing at least a full 2' of clamping surface.
As you can see from the photos, Matt has even gone so far as to shape the terrain so that
it matches correctly in either configuration.
(For the record, the track in these photos was laid by John Drye and Charles Greenacre. Thanks to Matt for providing the photos and for valuable feedback on this page.)
One of the goals I had in coming up with this design was that I wanted to eliminate that 1" of slop. I wanted the module to displace each side of the layout in nice even foot increments.
More importantly, I wanted to be able to incorporate a mountain line, since (so far) all of our modules have a mountain line.
What I came up with was essentially a quarter circle divided into two sections. The sections can be assembled with the three lines to the outside, or they can be swapped to place the three lines on the inside. It's simple, elegant and it works.
The one draw back is size. In order to keep all the turns within NTRAK specs, the arc needs to cover a six foot square.
However, each section by itself is not much larger than a standard four foot module so it's really not so bad.
One advantage to this design is that it's really very simple to construct. The top for each module can be cut from a 2' by 4' 3" rectangle. (Actually it's 6 * SQRT(2) / 2 feet but 4' 3" is close enough.) Simply find the center of the rectangle and cut on a line that bisects the rectangle at a 12 1/2 degree angle. Then reverse one of the halves and put them together again. From that you can make all the other necessary measurements.
Another advantage is that if you build two of these, you can add them to just about any existing rectangular NTRAK layout, converting it from a rectangle to an "L" shape. In other words, if you already have just enough corners to make a rectangle, then adding two of these to your layout generally won't require you to come up with any non-standard length modules.
This design is an attempt to make up for the size deficiency of the six footer.
It's basically a simple variation on the same theme, only compressed about as far as you can take it.
If you are very careful about laying out the turns, you can just barely stay within the NTRAK specs.
This design is a little more difficult to construct, but it's not too bad. Measure the position of the tracks from the end of that 5' measurement; not from the corner in the middle because that face is a little longer than 2' (5 - 2 * SQRT(2) feet to be exact).
There is one very minor disadvantage to this design (one which Matt's design shares). The inside corner measures differently from the outside corner. This wasn't an obvious disadvantage to me at first but after I tried fitting a pair of these corners (on paper) into our existing layout the problem became apparent. It can't be done without a couple of odd lengthed modules (1 foot, 3 feet, and so on) to make up the difference. For many large groups this isn't a problem, but for small groups like ours, where we're lucky to have what we've got, it can be.
Because the module displaces the track by five feet when used as an inside corner and by four feet when used the other way, you end up with an extra foot in each direction that you can't account for. As long as you've got a couple of odd lengthed modules lying around or a three foot outside corner you can pair with the five foot inside corner then you're all right.
And finally, one interesting little feature that both of these last two designs share is that they allow you to put modules on 45 degree angles instead of the usual 90 degrees. After all, they're each really just a pair of reversing modules with 45 degree bends in the middle.
In fact, if your layout is large enough, you can insert a four foot module in between the two halves, making the whole assembly measure nearly the same as an 8' 2" corner. That gives you 2" of slop to deal with but a larger layout should be able to absorb that without too much of a problem.