Curious about P48?

     W tend to take reliable wheels for granted today. Many younger modelers won’t remember a time in the hobby when it wasn’t this way. However in the early days of

model railroading, wheel profiles and dimensions were all over the place. The NMRA had begun to set standards and recommended practices, but many man-

ufacturers were still doing their own thing.

     P48, also called Proto48, had its beginnings in the 1950s when a group of  On3 modelers at the East Bay Model Engineers Society in California wanted to lay dual gauge trackage. There were different wheel standards for the narrow gauge equipment, mostly based on OO profiles, which were frankly just plain ugly. The real interest in using scale wheels came from Dan Ranger and Norm Buckhart who decided to build a model of a Rio Grande C-16. This project led to the discovery of an 1890 Railway Equipment Guide which had a whole chapter on wheel profiles and specifications. This volume provided the missing insights about why wheels are shaped the way they are. This in turn, led to the development of the first true-to-scale wheel contour in O Scale, having a tread width of .117” with a properly formed fillet between the tread and the flange (a key to good operation) and scale-sized flanges of 0.028”, made by Al Henning of St. Louis, who was a skilled machinist and also a model railroader. This was all in narrow gauge (On3) running on Code 100 rail.

     The new wheel profile ran beautifully. One of the members, Don Graf, had some standard gauge equipment made up with prototype wheel specifications and the group discovered that they also tracked well and were compatible with narrow gauge. However, when an attempt was made to run the traditional O Gauge equipment, they quickly discovered that the oversized flanges were too deep for the Code 100 rail and the wheels wouldn’t track properly through the dual gauged turnouts. The issue of course, as we now understand, was the relationship between the frog’s flangeway dimensions and the wheel flange’s. You either had to lay the track to fit the existing O Gauge wheels or the new prototype based wheels since the two were incompatible.

     Many attempts were made to design a turnout frog that would accommodate both wheels, but they were futile, the two just weren’t going to work together. This became a source of much conflict, because of all the existing equipment used the NMRA specs, meaning everything would have to be converted and wouldn’t be able to run on anyone else’s layout. An impasse was reached and the narrow gauge modelers went their own way in time.

     Afterward, Norm and Don wondered to themselves, that if existing standard gauge wheels wouldn’t work with the narrow gauge specs, than why not just make everything to “scale” dimensions including the track gauge and be done with it? This was the beginning of the Proto:48 movement.

     As is often the case with change, these “new” ideas were not well received in the O Gauge community of the time; mostly due, I suspect, to the lack of compatibility between the two standards. So, advocates for the new prototype movement had to fend for themselves for wheels, often having them made by someone who had the resources to do it, or even doing it themselves. In the 1980s, the NMRA had a change of heart and adopted a set of standards and Recommended Practices (RPs) for prototype based track and wheels along with the name Proto: 48 to distinguish the new standards from the historic 1-1/4” O Gauge standard. The term “Proto” was chosen due to its applicability to other scales that were also experiencing a finescale, or prototype movement.

P48 Today

Modeling in P48 today is a joy compared to those early days. Many more components and suppliers are available making the transition a fairly easy one. 

1/4” scale allows for a level of detail that many of us longed for in the smaller scales. And while outstanding craftsmanship is possible in P48, you don’t have to be a master craftsman to get started. As with all the popular modeling scales, there are folks with many different skill levels from rank beginners to those doing outstanding work. Personally, I consider myself a beginner. I had scratchbuilding experience before coming to P48, but I’m hardly an expert. One of my reasons for the switch was to develop such skills more fully.


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Copyright 2012 Michael L. Cougill