This is a simple jig for performing quality control checks on locomotives and cars.

The "surface plate" jig is fully described in the "Building a Surface Plate" article in the March 1996 issue of Railroad Model Craftsman. The article appears on page 81, and is written by Chuck Davis.

In that 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 bottom of 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.

I started off with a 16" by 6" piece of plywood upon which the jig will be built.



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 is 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.



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.

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.



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.



This completes this simple jig. The remaining photos show the jig in use.