Track Geometry, or Two Parallel Lines

What they don’t teach you in geometry class is that low-grade 5/16″ plywood has a mind of its own, especially if it has ever gotten wet.

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Navajo Mine Railway Track
Jointed rail on the Navajo Mine Railway

Of all the math courses I took in junior high and high school, the one in which I actually got decent grades was geometry.  I suspect it’s because the subject made sense.  It wasn’t dealing in the abstract but instead it had immediate real-world applications.  (Apologies to all the math teachers out there; I get it that you have to be able to crunch the numbers before you can apply them.)  In fact, that geometry class may have been my favorite one at Fairview High, despite the teach’s terrible 1970’s comb-over.  I mean, really.  When you can see shiny scalp between the bryl-creamed strands of hair, who exactly do you think you’re fooling?

But I digress.  Geometry, and especially trigonometry, have proven more useful in my world than almost any other subject I learned in school.  Yeah, I got mediocre grades in English!  A person can use trigonometry to build stuff.  That and an understanding of the concept of pi are sufficient tools to design things like, say, a model railroad.  Well, that and a few carpentry skills, which I picked up from my dad and my other favorite class, wood shop.  (Why not two favorites?  Why choose between pizza and a hot fudge sundae?  Gimme both, say I!)

What they don’t teach you in geometry class is that low-grade 5/16″ plywood has a mind of its own, especially if it has ever gotten wet.

So let’s fast-forward about 21 years after my graduation from high school. One week the family was out of town, so I used the evenings to throw together some benchwork for a layout expansion in the spare room. My design called for using the conventional cookie-cutter method to create the subroadbed.  I visited Hacienda, came home with all the requisite materials **, and stockpiled them on the back porch for the following day when I would start cutting.  Unfortunately the next day it rained while I was at work. Not to worry, I said to myself; the wood will behave if I use sufficient supporting risers between the subroadbed and the supporting 1X4 framework. I should have worried.

(** Why use such thin plywood for decking?  Because, in turning a helix, it enabled me to reduce the grade just a smidge since the structure above the lower levels was a bit thinner.)

Turns out, my materials had acquired some new un-flatness, and I was never really able to completely train it out of the wood. Plus, thin plywood doesn’t warp consistently in every direction anyway; it actually does have a bit of a grain.  And here’s the thing: laying tight-radius track on a grade with reverse curves is a recipe for disaster anyway. Throw in a few unplanned humps and dips and you will never reliably keep a train together. It’s like installing multiple yard humps out on the mainline; those Kadees just slide apart. (Hm, a model hump yard with scale retarders?  Who wants to give that a shot in 1:87?  I can tell you, the hump part will work just fine!)

Okay, now move forward another decade. We’ve moved to a new house and I’m rebuilding the railroad in a larger space, using many of the components from the prior installation. This, of course, means that I’ve incorporated the same warped roadbed in the construction. Truth is, I never operated the former version enough to realize how bad the track geometry problems were. Now, however, I have a much longer, fully ballasted mainline and I’m operating longer trains with (this is significant) a lot of 86′ cars. Turns out, cars less than 50′ are Labrador retrievers, pretty forgiving of squirrelly operating conditions. An 86′ flatcar, on the other hand, is a rich sorority girl; it wants to be treated like a little princess or it uncouples, or goes off the rails. I had a whole yard full of prima donnas.  So, what to do? Go our separate ways, or fix the relationship?

This is where it’s useful to ponder the seemingly-obvious fact that we’re modeling actual railroads, only smaller. Real railroads face similar challenges, although they’re usually smart enough not to install a 40-degree curve on a mainline! No, they have track geometry problems of their own. Take a look at the header photo, which I snapped of the track at my former employer.  What solutions do real railroads bring to the problem?  Well, two immediately come to mind.  One is to contract a rail grinder company to visit and to smooth out the railheads.  Another is to get the section gangs or other contractors to level the roadbed, lifting track when necessary, and get everything more-or-less on the same plane.  It turns out that the first solution is tough to employ on a widespread basis in scale applications, whereas the second holds far more promise. And that’s where I am going to spend the rest of our time today: how to level out your track by lifting and re-ballasting.

Okay, first a couple of assumptions. First, I use flextrack, basic old Atlas Code 100 in my case, but any flextrack will do for this. You must be using some kind of flex track or scale “panel” track; hand-spiked track is beyond our scope.  Second, I’m ballasting my track and so must you. The type of ballast is up to you. On my railroad I go mostly for a darker shade to represent the D&RGW’s slag and scoria that they used for years. It’s a blend of 50% commercial black ballast and 50% coarse sand.  In other words, sand that’s roughly the same size as the commercial ballast. Third, I’m using mostly cork roadbed, because it’s easy, firm, and has a good profile. It’s also possible to use craft foam cut into strips; I actually use large sheets of this to underlay my yard trackage, but use multiple strips to elevate mainline bypass tracks around the yards.

Other tools and materials?

  • A short straight-edge, such as a small level, between 8″ and 12″ in length.
  • A tack hammer.
  • A nail set.
  • An inexpensive chisel.
  • A medium-soft paint brush
  • Track spikes, something a little longer than normal since we are lifting the track higher than normal.
  • A bottle of white glue such as Elmer’s (don’t go with the cheap dollar-store stuff!!!).
  • A squeeze bottle for diluting the glue, such as your previous Elmer’s bottle.
  • A spray bottle, such as you might use for plants or laundry or training the cats. Just be sure you tell your wife that you’ve borrowed hers. A better solution is to purchase your own dang bottle…

Now that you have all that stuff in a pile, let’s examine your track. First of all, you probably already have some idea where the problems live, but I’d suggest the following: assemble a short train of long cars, such as piggyback flats. These are best because there is little in the way above the deck line and you can most easily observe the action of the couplers. Now, run the train slowly around the railroad, walking with it and observing any bobbing of the ends of the cars. See if there are places where one car’s coupler lifts away from the adjoining car. Sometimes it’s obvious and other times it may take a few runs. Once you identify the spot, mark it somehow.  You’ve found a high spot, which means that on one side or the other is a sag.  The sags are what we must locate, and this is where the straight-edge (your short level) comes into play.  I use a level not because of its leveling features, but because it’s thicker than a ruler. This aids you in the process.

Place the level atop the railheads at the high point, and move it each way, eyeballing it from the side. You should be able to see where the track dips away from the straight-edge.  Go out some distance in each direction from the high point. This can be tricky if it’s on a curve and even more so on a curving grade, as there’s a helical shape introduced into the track now. More on this later.

So, now you’ve found a sag.  This is important since it’s far simpler to lift a sag than to undercut a high spot.  We will focus on dealing with the sag.

Assuming that your track’s been nailed down already, here’s what you do.  Take the chisel and whack chunks out of the plywood.

No.  No.  I’m only kidding!  That is not what you do.

(Take 2) Locate any track nails in the area, take the chisel, rest it on the railhead, and use its sharp edge to gently lift the nails up from the sub-roadbed. Yes– we are using the chisel as a crowbar. Once you have loosened all nails in your sag, gently loosen the track from the ballast.  I’m assuming here that you had glued the ballast when first installed. Sure, you could just demolish the first ballast installation, but that’s really not necessary.

— And here’s where I am going to take a giant step backwards and pretend that I was smarter back when I first installed the ballast. Here’s the secret: you can do all of this before you put the ballast in the first time! Saves much time. If you haven’t yet ballasted the track, simply adjust this process.  You’re smart and I’m confident that you can manage it.

OK, back on track, so to speak.  Now that you have your sag loosened, you want to try to get the railheads as level as possible, longitudinally and laterally. (Also, it’s kinda important that you don’t work on too much track at a time, lest it drift off alignment.)  Okay so far?  Now you have a loosened piece of track hovering above the roadbed. Take a Dixie cup full of your preferred ballast, and gently sprinkle it down the center of the track  Not much, mind you.  Just enough to work between the ties and get under the track. Work this in with the brush, tamp by gently tapping on the track, and re-check things with the straight edge. Wash, rinse, and repeat as necessary until the track has been leveled across the sag (without creating a new hump. That would be defeating the purpose, you see). Once it’s to the desired grade, ballast outside the rails, being sure to fill any voids caused by lifting the track.

Now, we fix it all in place.  Mix some glue about 50:50 with water in the small squeeze bottle.  Gently spray the track with the spray bottle to moisten things.  Using your squeeze bottle, flow the glue mixture into the ballast, thoroughly saturating it.  Be sure you saturate it all!  Now, go away and do something else for a day or so.

After the ballast has hardened, gently push the track nails back into place.  If you didn’t move anything, they should find their former holes and go right in.  You really don’t want to pound on anything at this point, but you can use the tack hammer and nail set to seat any stubborn nails if absolutely necessary.  But remember: be gentle! And accurate too, let’s not forget about that. The nails are not really holding the track down now; that’s being done by the ballast and the glue.

Polish the railheads to remove any extraneous glue or haze, inspect for any stray chunks of ballast that might interfere with a flange, and send the test train back over the spot.  You should notice a marked improvement.  Chances are, there will be other sags and humps, sometimes revealed by fixing one like this.  I had to lift an entire section of track, two or three feet long, to deal with a serious dip. Just fix whatever you must, until your trains stay on the rails better.

The result: You will be so glad you leveled your track. It makes such a difference. actionroadlogobang

A comment on superelevation. This, for those who may not be familiar, is simply the technique of banking railroad track on curves, much as in Nascar or at Indy, right? It seems like a really good idea, so I tried it on my railroad.  Um, it was a disaster. Here’s why: I’m dealing with pretty tight radii, down to 24″ r at times. I know, I know, curves that sharp look terribly unrealistic, but space constraints are a reality.  Well, if you think about superelevation, you are essentially laying track around a bowl. If you have long cars such as 85′ passenger cars, auto racks, or pig flats, what happens is that the trucks lean up so that the outboard axles are pushed higher. Combined with the fact that the trucks are already turned to the side, the outer ends of the trucks will probably hang up on the underside of your car and derail. If you superelevate a curve on a grade, it’s even worse–it’s like climbing a corkscrew.  I ended up abandoning the effort, removing all shims from my track and reverting to level track. In some ways it would almost be better to lean it out than in, at my curvatures! Sub-elevation?  Hm.  But no, I draw the line at some things.  I would not recommend superelevating any curves at less than about 48″ radius in HO scale, proportionally adjusted for other scales.

Author: ACTIONroad

I'm a model-builder with pretensions of being an author. Here's where I will write the stuff that will never make it into a book or magazine...

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