Sunday, May 16, 2021

Modeling passenger car diaphragms

 The diaphragms on passenger car ends, used to secure passage between cars, beginning late in the 19th century, have always been a challenge for modelers. It isn’t that they are themselves difficult to model, it is because the curves and switches of our model trackage are so much sharper than the prototype. Inevitably we have to make a few compromises — as with so many modeling topics. 

I will begin by describing the prototype diaphragms used on heavyweight cars, particularly Pullman sleepers. These are about the oldest passenger cars I would encounter in my modeling year of 1953. Shown below is a clear view of the “standard” Pullman diaphragm, on the sleeper Alazon (a 12-1 floor plan, meaning 12 sections, 1 drawing room). The photo, dated December 2, 1927, is by Pullman (Rob Evans collection).

You can see the main features here: a face plate, which mated with the adjoining car’s face plate; a bellows of heavy canvas, with a metal frame inside; and a folding gate, closed up at the left side of the opening. At this time, diagonal stabilizer bars —also sometimes called tension rods, anti-rattle bars, or support rods — were not in use (more on those in a following post). 

There has long been an “acceptable” HO scale model version of this diaphragm, Walthers part no. 933-429. It consists of a face plate, of vinyl plastic, and a folded paper representation of the bellows. These are now described on the Walthers site as “availability discontinued,” presumably meaning permanently. One can still find them in some hobby shops, and from various on-line sellers.

I have used these Walthers parts in past years, and the model below is an example of how they look. I think you can see some shortcomings, compared to the photo of Alazon at the top of this post. The rim around the face plate is too wide and the bellows really too deep. But in a coupled-up consist, there is something between the cars, and if, as is often the case, our car spacing is larger than prototype, the over-deep bellows compensates.  

The model here is a Ken Kidder brass “Harriman” baggage car, though the arrangement of roof vents is closer to Illinois Central cars than to SP, and with Central Valley trucks. 

Naturally there have been numerous suggestions of ways to improve the Walthers product. One example, to make a better face plate from styrene sheet, was shown by Bob Zenk in Mainline Modeler, in articles in both 1981 and 1984. I showed the same approach myself, in a magazine article in 1984, referenced in an earlier post (see it at: ). That same post shows my face plate drawing. 

Another suggestion for improvement of the Walthers diaphragm is that you can remove one or more of the folds from the bellows, making it less deep. I will show this later.

Over the years there have been many commercial alternatives to the Walthers diaphragms, which I won’t review here. But for really excellent diaphragms, it is hard to beat the detail, accuracy and multiple designs of the Hi-Tech Details kits. Here’s a link if you’d like to look at the range they offer: . At this point, I will postpone further comment of my own to a future post or two.

Tony Thompson

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