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Railcar axles

Railcar axles

Railcar axles

Hi All,

Curious if someone could tell me the typical diameter of a railcar axle. I believe the journal bearings are typically 6-1/2"x9 or 6-1/2"x 12, etc. Does the the 6-1/2" give any indication on axle diameter? If it helps the railcar in question is 4 axles rated for a max of 286klbs.


RE: Railcar axles

That will vary a bit with type of car and location. Assuming North America, I would find an AAR Handbook.

RE: Railcar axles

The 6&1/2 x 12” refers to an AAR std. journal size or tapered roller bearing size. The axle dia. varies all over the place from end to end to fit the bearing size and transitioning to the wheel bore size, and then taper slightly to the center of the axle and is 7&3/8” at the center, for only about 6”. That’s a std. “F” class axle, a std. 100 ton axle and its max. axle loading is 71.5k/axle, or 286k for a four axle car. What kind of car are you looking at? I am not aware of a 6&1/2 x 9” bearing or axle, certainly not an AAR std. There is a class ”E”, 6 x 11”, 70t std., g.f. 55k/axle and a class “G”, 7 x 12”, 125t std., g.f. 78.75k/axle, on either side of your axle. Various AAR Stds. and manuals have all the gory details for these various std. components, they are tightly toleranced, and tightly controlled by the AAR, because they must run on all of the railroads. For the most part various RRs can’t/don’t have their own stds. for these components. They may have their preferences as to manuf’er., but not as to the std.

Itsmoked’s photo is not a std. three piece freight car truck. That is probably an old passenger car truck, maybe some transit equip., given its general arrangement and brake discs and springs and snubbing, etc. The term tapered refers to the tapered roller bearings which are std. today. I’m not sure where the Santa Fe info. came from, but everything I ever designed and built for them, maybe a couple dozen special railcars, used std. AAR components, sometimes with their preference for a specific manuf’er. for some specialty components. They were really a first class RR and a pleasure to work with, their Mech. Dept. was top notch and generally easy to deal with. I had a number of good friends there.

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