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The IR Scale

Existing Model Railroad Gauges

Diamond Crossing
Real Life Indian Railways broad gauge

There are a ton of gauges to choose from when it comes to model railroads. OO, HO, TT, N – the list is endless really. Each one, defines a different distance between the two rails. As shown in the graphic, the standard HO Track or HO Gauge has this distance fixed at 16.5 mm.


Allied closely with the HO Track/Gauge is the HO Scale. It was designed to build model of real trains which ran on tracks where the rails are placed 1435 mm (4 ft 8.5 in) apart.

Needless to say, they weren’t Indian. Our rail tracks (for broad gauge) are 1676 mm (5 ft 6 in) apart.

A little more clarification is due on the mild condescension on non-Indian-ness. According to the HO Scale :


16.5 mm (HO track/scale) ≡ 1435 mm (real track)


which implies that


1 mm (HO track/scale) ≡ 86.969696…. mm (real track)


So, the HO Scale is actually a 1:87 scale. Which means that every 1 mm of dimension on an HO model represents 87 mm of “real life” dimensions.


Working with the HO Track/Gauge is nice because it is rumoured to be the most popular railroad modelling standard in the world and tracks and other accessories are easily available. So I chose the HO scale to build our trains.


However, there are problems.


If the calculation is repeated using the Indian Railways broad gauge measurements, then the scale comes out to be 101.575757…. . If I round off (as engineers are prone to do), then I come up with a 1:100 scale for Indian Railways models.


Every kit-bashing solution we tried built a weird Indian Railways model. That’s primarily because of the 1:87 scale that HO is built on. But we’re perfectionists. At least I am…

Enter 3D Printing

There are people in this world (us included) who go fairly crazy at the idea of having a scale model of something that they adore. And we adore trains. Especially the Indian variety since we grew up in and around those…

So, I invented the IR Scale. Its not patented yet, so you can go ahead and copy it. We’re not that big on idea protection. Also, because I have tons of other ideas. Anyhow, I digress. I’m going to describe it now…


I kept the HO Track – that’s 16.5 mm gauge. And designed the models from scratch. I knew that TheTrainMaker could do his part on the 3D printing end. And we used this technology to build our very own IR Scale 1:100 scale models.


The good news for prospective end users of course was that all these models could be made to stand on a standard HO track that could be picked up anywhere in the world.

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