Articles - Coupler Height Gauge
11/03/2008

N-scale Version

This is a simple jig for performing quality control checks on locomotives and cars. The jig is fully described in the "Building a Surface Plate" article in the March 1996 issue of Railroad Model Craftsman. I have built both an N-scale version and an S-scale version. The N-scale version is described first. In the above-mentioned article the author uses two sheets of styrene to form the jig. I found that to be a bit too much of the precious styrene, so I built mine out of a piece of left-over plywood and one sheet of styrene. The idea is to create a raised platform so that the wheels' treads ride on the styrene. You can then perform all sorts of checks, such as coupler height, wheel flange heights, squareness of the car's trucks, and even mark off horizontal lines for placing decals. The jig takes less than an hour to build. For the N-scale version, I started off with a 16" by 6" piece of plywood upon which the jig will be built.
Coupler Height Gauge
Then I took a 12" by 6" standard sheet of styrene and cut it into two sections. First, the thickness of the styrene matches the height of my rail, which, for N-scale, was 0.040. The idea behind this effort is that you can immediately check to see if your wheels' flanges are too high to ride on your layout's rail. Following the magazine article's idea, I cut one section about 4 inches wide. By making one strip of the styrene wider than the other the jig provides resting space for a machinist square and other tools that need some extra, flat surface space.
Coupler Height Gauge
Next, I glued the two strips of styrene to the plywood base with superglue. I thought about using other glues, such as rubber cement, but superglue works, and it dries fast, allowing the jig to be built in under an hour. I used the NMRA gauge to determine the spacing between the two pieces of styrene. The locomotive and car's wheels will be riding on the styrene surface, so gauge is important. A couple of metal weights are shown in the photograph ensuring a good, tight fit between the styrene and the wood. The tighter the fit, the better the glue will work.
Coupler Height Gauge
The fact that the plywood piece was longer than a single sheet of styrene gave me the idea of adding two pieces of code 40 rail to the remainder of the jig. The reason for this is so that I have some extra space on the left side of the jig.
Coupler Height Gauge
And the reason for the extra space is that I superglued the Micro-Trains coupler height gauge on the jig. The right side of the gauge has an N-scale coupler to verify coupler height, and the left side of the gauge has a surface that allows us to check whether the coupler, once installed on the car or locomotive, will sit at the correct height. I have always done this check on a piece of track, and that is a pain, especially if the track has scenery around it. This jig allows me to do the coupler checks on the workbench. I superglued the gauge to the jig, because I have no other use for the gauge. I also seemed to misplace it from time to time; this way it is much easier to find! I located the gauge such that there was 9-1/2 inches of space to the right of the gauge on the jig. This is the length of my longest steam locomotives with their tenders attached. There is about 5 inches to the left of the gauge, which is enough for passenger cars.
Coupler Height Gauge
This completes this simple jig. The remaining photos show the jig in use.
Coupler Height Gauge
The hopper can be checked for whether or not a spacer is needed between the coupler and the body, and the Z-scale coupler mounted on the passenger can be checked to see if it is at the correct height.
Coupler Height Gauge
Wheel flanges can be checked by seeing if the wheels' treads actually ride on the styrene or not.
Coupler Height Gauge

S-scale Version

For the S-scale version, I started off with a 15" by 6" piece of MDF upon which the jig will be built. Any base material will do, as long as it stays flat over time. The length depends on the equipment to be checked. I will be running mostly 40-foot or so equipment, so mine is large enough to handle a 50-foot car or engine, just to be safe.
Coupler Height Gauge
After measuring S-Helper Service's flanges, I realized that 0.040 is thick enough for the wheels to ride on (if you use deeper flanges on your equipment, you'll have to adjust the thickness of the styrene accordingly). The point is that the bottom of the wheel flanges shouldn't ride on the base. I cut two one-inch strips of 0.040 styrene and glued them to the base using superglue. The height of the styrene verifies that the wheels all adhere to a minimum flange height. I glued the styrene pieces the same distance apart as my rails on the layout, so that wheel gauge can be checked quickly.
Coupler Height Gauge
The next step was to deal with being able to install couplers on my cars and engines so that they all line up with each other. I settled on a scale 3-foot height from the tops of the rail to the vertical center of the coupler. People typically use the Kadee coupler height gauge for this check. That works fine, but what I really need to know is, do I need to adjust the truck/body height so that the coupler will wind up sitting at the correct height? The Kadee coupler height gauge also checks for that. But rather than spend $15, I decided to just make my own. Also, from my experience with the N-scale jig referenced above, it is a pain to only have one of those gauges on one side, because I had to always pick up the cars and engines and flip them around to check the other coupler. Needing two Kadee coupler gauges would now total $30. After some measuring I concluded that two pieces of 5/8" thick MDF cut to 1/4" width will tell me exactly whether or not the location of the coupler on the car or engine will be correct. The next photo shows one of those pieces glued down, centered in between the two strips of styrene.
Coupler Height Gauge
This photo shows the coupler on this box car is at the correct height. The top of this S-Helper Service coupler matches the top of the draft box, which matches the top of the MDF block. If you use the metal uncoupler pieces, you may want to cut a little relief into the bottom of the MDF blocks, so that you can push the coupler right up against the block. My layout's standard is to not have those.
Coupler Height Gauge
This check is used to make sure the wheels' treads ride on top of the styrene. A matching piece of styrene can be placed elsewhere on the jig's base, and a machinist square can then be set upright next to the car to make sure the body sits perfectly perpendicular to the track.
Coupler Height Gauge