Re: CV Round Freight Car Roof

Richard Hendrickson

On Dec 27, 2013, at 7:55 PM, destorzek@... wrote:

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Richard wrote:

"It was a uniquely NP design and though I can’t say with assurance that it was never applied to other than NP cars, I’ve never seen any evidence of its use by other car owners."

"I am on the road and can't give the car series, but SOO used the identical roof on a series of box cars which is the only other owner I have heard of using the NP roof."

Jim Dick of the NP Historical Society is the guy with the documentation, but I'll give it a try from memory.

The NP's "circular roof" was patented by a gentleman named Robertson, who was an official in the NP's car department. Robertson's intention was to sell the roof industry-wide, and various correspondence from the NP files state at different times that the patented roof would be available from either Chicago-Cleveland or Hutchins, but there is no evidence that Hutchins company ever represented it.

The only road to use this roof other than the NP was the Soo Line, which specified it on all the boxcars they bought between 1926 and 1930, cars well represented by Sunshine kits. The Soo also used this roof on ten milk cars they constructed in their own shops in 1925.

Looking at the Robertson patent, the sheet metal is almost incidental, and the patent makes no claims on the design of the sheet metal covering. The crux of the patent is a system to key the wood roof sheathing so that it acted as one large shear panel, to counteract "weaving", the twisting of the carbody that caused the roof to rack out of square first one way, then the other. This racking was found to quickly wear the sheet steel panels that were just becoming popular as the weather covering of car roofs, and Mr. Robertson's design may be the first to address it.

Unfortunately, the other roof manufacturers took a different tack, designing flexible joints into their second generation of outside metal roofs, and Robertson's invention never really went anywhere. It did, however, appear to work, and most cars roofed with the Robertson design roofs kept them their entire lives.

Thanks, Dennis.  That’s an admirably detailed and succinct summary of the essential information about the NP’s “circular” roof.  Now that you have jogged my memory, I think I knew, but had forgotten, that the Soo was the other RR that used Robertson’s circular roof.

Richard Hendrickson

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