Wednesday, March 21, 2007 at 9:32 am

When Scale Isn’t in Gauge

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In his “Trains of Thought” column for the April 2007 issue of Model Railroader, Tony Koester muses on the different scales used on No. 1 track. You may be aware that “G scale” encompasses, in fact, many scales.

If the flanges of locomotives and rolling stock fit between the rails of No. 1 gauge track, [garden railroaders] cheerfully run it. It doesn’t matter to them that some of the equipment is scaled to 1:22.5 proportion, which assumes the 45 mm No. 1 gauge equals one meter, as in European narrow gauge; 1:20.3 proportion, correct for 45 mm equaling 3 feet; 1:32 proportion (No. 1 scale) for the standard gauge version; or the popular 1:29 proportion, which is oversize for No. 1 gauge track but looks okay. They’ll run it all.

If you’re a regular MR reader, you’ll recall that Tony built an indoor large scale project in 2005, and, otherwise fastidious about accuracy, he ended up settling on 1:29 scale rather than the prototypically accurate 1:32, because more of the equipment he needed — especially freight cars — was available in 1:29 than in 1:32.

Because two major manufacturers were interested in offering North American standard gauge trains for No. 1 gauge track, but trains and models made to the smaller, but correct, 1:32 size looked too small next to LGB’s 1:22.5 and Bachmann’s 1:20.3 narrow gauge trains. So they bulked up the models until the size was roughly equivalent to the narrow gauge offerings, but the gauge remained 45 mm to ensure operational compatibility.

Market compromises, in other words, resulted in standard-gauge stuff being modelled out of gauge, which you can tell disappoints Tony a little bit. But G scale isn’t the only place where this has occurred.

Drop down to O scale and you’ll see what I mean. O scale track is 1¼ inches (31.8 mm) wide, but American O scale is 1:48. In 1:48, 1¼ inches is a scale five feet, making every “standard” gauge O scale layout unprototypically broad gauge, since standard gauge is 1735 mm, or four feet, 8½ inches. But British O scale is 1:43, which makes 1¼-inch track correct and in scale.

A lot of U.S. O-scale modelling is in narrow gauge, but compromises exist there too. Most American narrow-gauge railroads were three-foot gauge, but most commercially available American models are 30-inch-gauge: On30 instead of On3. Every On30 model of a western U.S. narrow-gauge prototype is out of gauge. Why? Because On30 is exactly as wide as HO scale track, and that’s useful.

But it doesn’t stop there. HO scale and OO scale use exactly the same, 16.5-mm-wide track, even though HO is 1:87 and OO is 1:76. The reason OO is out of gauge is because British prototype locomotives were smaller than their U.S. counterparts, and at the time the standard was set, an HO British locomotive was too small to house a motor.

Look hard enough and you’ll see other examples: Nn3 uses Z-scale standard-gauge track not because it’s in scale, but because it’s there. At the other end, look at live steam: 1:8-scale trains — these are trains large enough to sit on — use either 7¼-inch (184-mm) or 7½-inch (190-mm) track, depending, it seems, on where you live. Neither, it turns out, is exactly in scale for 1:8 scale, but both are probably close enough — and easier to measure than a track gauge of 179.375 mm, or a scale other than 1:8.

Compromises exist, and exist for a reason. In practice, fidelity to scale is only one consideration of many; compromises may well allow something to exist that might not otherwise be feasible — technically or economically — if it had to be in perfect scale.

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