Tim O'Connor firstname.lastname@example.org [STMFC] wrote:
Tim & Andy,
Regarding the IMWX/RC or other versions of the 1937 AAR box car, it should be noted that like most other "standard cars," there were differences in the design that evolved over time. A couple of years ago I looked at every general arrangement and brake arrangement drawing available for ACF box cars built from 1934 through the 1950s. From this information is the portion that applied to box cars of the 1937 AAR design.
ACF built approximately 9,397 box cars conforming to the 1937 AAR design, and there were several variations involving the stringers.
The cars built from 1936 through May 1941 had 2 stringers, accounting for 5,512 cars. Of these, 3,503 cars had 2 stringers extending from bolster to bolster and diagonal bracing between the bolsters and end sills. The balance of 2,009 cars had 2 stringers from end to end and lacking the diagonal bracing. These two variants were essentially random throughout the 6 years.
In 1941, 850 cars built for Van Sweringen roads C&O, NKP, PM (July to Oct. 1941) and one car for the U.S. Navy built in 4-42 had an unusual variation with 4 stringers between the crossbearers, 2 stringers between the crossbearers and bolsters, and diagonal bracing between the bolsters and end sills.
The design changed effective with ACF lot 2300 (L&N cars built ca. 9-41) through lot 2714 (DL&W cars built in 1944), whereby 3.034 cars all had 4 stringers from end to end and lacking diagonal bracing.
Incidentally, there were also variations in the truck center dimensions. Most cars had 30'-8 1/2" truck centers, which was the A.A.R. design standard dimension for 1937 AAR box cars. Variations included ATSF Bx-27 cars with Duryea underframes with (30'-10 7/8"), two orders totaling 400 cars built in early 1941 for ITC & WLE (30'-10"), and two NP orders totaling 1,500 cars built ca. 3-40 & 5-41 (31'-1 7/8"). In the immediate postwar years, the 30'-10" truck center dimension phased in as the new A.A.R. standard dimension, but again, not without some variations.
Just passing this information along for inquiring minds. :)