Articles - Track Gauges
06/04/2017
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For each scale, the NMRA produces a steel track gauge. You need one, unless you only buy commercial pre-fabricated snap-track. For everything else, including commercial flextrack and turnouts (and especially if you hand-lay your track), you need one of these for your chosen scale. For S-scale the NMRA sells one for Sn3, but not for standard-gauge track. There is a complicated history there*, but you can get the standard-gauge track gauge from the NASG, instead. The NASG now also sells the Sn3 gauge. These gauges help you verify that the rails are the correct distance apart from each other. They also have notches for verifying that the locomotives' and cars' wheels are spaced correctly so that they will ride on the rails correctly. Finally, they provide tabs to check the proper distances of the various rails of a turnout. When you buy the gauge, it will come with a sheet that explains how to use each of the measurements. The N- and HO-scale gauges also function as a clearance gauge.

*The history was that in the ancient days, the standard-gauge NMRA's track gauge was not accurate as compared to the prototype. The NMRA refused to make any changes, so the NASG developed their own which was accurate. Eventually, the NMRA finally decided to accept the NASG's standard (their Sn3 gauge was accurate), and so any modern S-scale standard-gauge product is made to the, now matching, NMRA/NASG standard.
Track Gauges
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Although the above-mentioned gauge is the official authority on rail spacing, they are not easy to use when you are actually hand-laying rail. They are really more intended for checking existing track, rather than track construction. The gauge is not self-supporting, and the small tabs are hard to keep on the rails while you are handling other track-laying tools. So, most scales have manufacturers who make additional gauges out of various materials to help with this process. Shown in the photo below is a set of three code 83 S-scale track gauges I bought from Tomalco Track. I also have a set for code 100 rail. With these gauges, I recommend at least three. Three of them gives me reliable confidence that the rails are lined up correctly. Their flat tops are perfect for placing weights on them to weigh the rails down while you are working on the track. I also use these to lay curved track, although some people prefer the three-point gauges for that. Some people don't like that these gauges are made out of metal, because if the track is "live", they cause a short. Therefore some manufacturers make theirs out of a non-conducting material. However, the downside of some sort of plastic-based gauge is that if you have a soldering iron nearby to solder something to the rails, the gauge could melt. Both are valid solutions; you just have to pick the one that fits your working habits the best. I never have current applied to my rails while I am working on them, so metal ones are perfect for me.
Track Gauges
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A "clearance gauge" is a handy tool to have as well. These make sure that nothing overhangs onto the track to interfere with the running abilities of locomotives and cars. You need one of these if your layout has structures near the track (to make sure the platform, for example, isn't too close to the track), and for tunnels. They might also be handy for placing trees, telephone/telegraph poles and their wires, etc. There are three clearance-gauge standards, so be sure to pick the one for the era you model (as railroad equipment got bigger in the real world, the clearance needed for tunnels, etc. had to be adjusted to fit that equipment). In S-scale, the NASG used to sell a clearance gauge, but production costs and relatively low demand for them, has led the organization to not produce any more when they sold out. Well, if you model in S-scale, you learn how to build things yourself. That is a big part of the appeal of the scale. The clearance gauge dimensions are readily available on the NASG web site (the NMRA has them for the other scales as well), so I set out to make one for myself out of 3/4" plywood. Any gauge needs to be dead-on accurate, so this photo shows the tools I used to actually construct what amounts to a small block of wood (in addition to the table saw).
Track Gauges
Here is my final build. One of the notched-out corners in the bottom of the gauge is supposed to be "filled" with a 45-degree corner, but I couldn't figure out how to do that with the tools I have. That 45-degree is used to determine the clearance of braces on deck girder bridges where the braces are used to hold up the side panels of the bridge. What I may do down the road is cut a 9/32" square piece of stock, and then slice it down its middle diagonally, and then glue that into the corner of one of the notches. Otherwise, it is just something I need to remember when I get around to building one of those types of bridges. The gauge is meant to be placed on top of the rail head, so there are no notches needed for the rail. In use, you do have to make sure that the gauge is properly centered on the rails to get accurate estimates.
Track Gauges
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When laying track for spurs, yards, or industry, where track parallels another track, it is important to provide enough spacing between them so that equipment on the track doesn't run into each other. Basically, on straight, parallel track, the track-center-to-track-center spacing should be at least 13 feet apart. If you hold operating sessions on your layout, and you have people managing staging yards (where the occasional human hand has to lend a hand after a derailment), the NMRA suggests a minimum of 15 scale feet of spacing. If you have ever seen a model railroad in action, you know that our curves are substantially tighter than track curvature in the real world. This causes equipment to hang over (i.e. away from) the track. If you have two such tracks next to each other, you have to lay the track in such a manner that two passing trains don't hit each other. This largely depends on the equipment you plan to run on your layout, and how tight those curves are. The NMRA has developed a table that lists the track-center spacing for various equipment types and various radii of the curves. I decided to make my own track-center gauge as I need one to build a coal tipple yard. I decided to make one just for parallel straight track. If I need others, they are easy enough to make. I took a 3"x1-1/2" block of solid wood (poplar in this case) and marked off where the 13-foot marks would need to be. Since center-to-center can be measured at any spot along the tracks, I made mine such that it has notches in it for a rail. These can be for either the two left-hand rails or the two right-hand rails of the tracks being measured.
Track Gauges
Because of the fact that this gauge needs to span a certain distance between two tracks, I don't know what kind of interference there might be between the tracks (scenery, ballast, etc.), so I decided to hollow-out the spacing in between. I left about a scale foot of material to either side of the 13-foot marks I made on the wood. I then carefully cut out a notch in the gauge, with a handsaw, where the rail is supposed to sit. I cut the notches to the outside of the 13-foot marks, because you want 13 feet between the "insides" of the two rail heads. The kerf of the handsaw blade was skinnier than the code 100 rail heads (the rail I currently use), so I had to carefully widen the notch by cutting the outside of the kerf again with the handsaw. The middle clearance is 1/2" tall. That I did with the tablesaw, simply nibbling away at the material (other tools can be used as well). As you can see from the photo below, this is how a track-center gauge is to be used.
Track Gauges
By making it out of 3/4" thick wood stock like this, it can be self-supporting while I am working on laying my tracks. I marked "13" foot on the gauge, so that if I build others in the future, I know which one to grab when I am laying track. This is an easy-to-make gauge, if you have the tools.
Track Gauges