Making an NMRA Weight Ruler

National Model Railroad Association, or NMRA, sets standards for model railroading. This makes models from different manufacturers compatible with each other, and it ensures better operation. One of the standards, practice 20.1, addresses the topic of weight. Without a standard for weight, a long freight train with cars from different manufacturers could potentially derail due to different things. Having lighter cars in the middle of the train, for example, could cause the train to tip over on a curve. However, NMRA set a standard for weight so this becomes less of an issue.

NMRA 20.1 is actually pretty simple. The numbers are different for the different scales, but it works the same. I will use the HO scale numbers, because that's what I model. For HO scale, the standard is 1 ounce starting out, plus half an ounce for each inch of length. It's a simple formula, however if you have a whole fleet of freight cars to standardize, it can get tedious doing the math for every car. That's where the ruler comes in. Because the standard is based on car length, I made a ruler that instead of measuring inches, measures NMRA weight standard. You simply hold the ruler up to the car, and the closest number to the end of the car is how much NMRA says it should weigh. Let me explain how I made this ruler.

I started out with a piece of sheet styrene. Thickness really doesn't matter for this, so I used a thin .010" sheet. I cut it into the shape and size of a ruler. I just used a ruler I had as a template, and cut around it. My NMRA ruler is 12 inches long, which is fine because only articulated cars are longer than that, and for those you can weigh each section separately. Next, I spray painted the styrene a hideous light green color. Any light color will be fine. I just don't want to see a styrene strip on my workbench and think I can cut it up for a project, just to find out it was my NMRA ruler! After letting it dry, I set my regular ruler next to it and marked every quarter inch on the styrene with a ballpoint pen. You can go closer together or further apart if you want. Further apart means less accurate measurements. I think every quarter inch is close enough, because at that point you're talking about a difference of 1/8 of an ounce, which in't much. Then, starting at one end, I started with the number 1 and went up every quarter inch, so 1.000, 1.125, 1.250, 1.375, etc. until I had reached the end of the ruler. Then I wrote that it is a NMRA weight ruler, and sprayed the whole thing with dullcoat to seal it all together. Now, thanks to a simple project, I don't have to do any math when checking my freight cars for NMRA weight standards!

My NMRA weight ruler. I marked every quarter inch with the NMRA weight standard for that measurement. I thought of decaling the numbers to make it legible, but decided that was too much work and wrote them by hand instead.

By putting the end of the ruler at the end of the car not in the photo, I can see right away that the car has to weigh 4.75 ounces to be up to NMRA standards. No more math for weighing freight cars! By the way, does the car look familiar?