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[quote user="Bucyrus"] Prior to this thread, I had not considered the function of the knuckle pin.  I simply took it for granted (falsely) that the knuckle pin was loaded by the pull through the coupler, as is the case with the original Janney coupler.  With the original Janney coupler as well as several imitators, the tractive force was transmitted to the knuckle and tried to swing the knuckle open, by pivoting it on the knuckle pivot pin.  Somewhere along the way to today's coupler, there was a sea change in this knuckle functionality.  Apparently the locking pin does not engage the knuckle tang in a way that prevents the knuckle from pivoting, but rather, in a way that prevents the knuckle from being pulled directly out of the coupler body in a straight line that matches the train centerline.So the fundamental difference between the early Janney design and today's coupler is the relationship of the locking pin to the knuckle tang. [/quote]Well I have taken a close look and I must retract much of the above which is extracted from my post yesterday.  There has been no fundamental change in the relationship of the locking pin to the knuckle tang between today's design and the original Janney design.  In both cases, the locking pin only prevents the knuckle from pivoting.  In the modern design the locking pin does not prevent the knuckle from pulling out in line with the direction of tractive force.The force bearing ridges that cordon calls out in his sketch are indeed located on the coupler per the sketch.  There is one set on the topside and bottomside of the knuckle tang, and another set top and bottom very near the knuckle pin.  The mating surfaces of these sets of ridges are shiny, indicating that they do bear a load.  There is also a set of force bearing ridges top and bottom of the knuckle about midway, and these ridges bear a load when the coupler is in compression.  They are also shiny.  There are also shiny and quite distressed surfaces on the coupler tang where it swings against the locking pin.And this is the part I found most interesting:  When the knuckle is closed with the locking pin locked, and the knuckle is pulled, it does transfer a reaction force to the knuckle pin.  So the knuckle pin does indeed bear a shear force when the coupler is transmitting the pulling force of the locomotive.   So this reverses my conclusion in the first paragraph above in that what I had taken for granted originally is correct. Therefore, when the coupler is under the loading of pulling the train, it shares the force with the following components:1)   A set of force bearing ridges on the top of the knuckle tang.2)   A set of force bearing ridges on the bottom of the knuckle tang.3)   A set of force bearing ridges on the top of the knuckle clasp body.4)   A set of force bearing ridges on the bottom of the knuckle clasp body.5)   The mating surfaces of the knuckle tang and the locking pin.6)   The hinge features of the knuckle, the coupler body, and the knuckle pivot pin.Items #1-4 prevent direct pullout of the knuckle in line with the direction of the train.Items #5&6 prevent the knuckle from pivoting.There are still a couple of points to ponder.  One is the question of how so many load carrying features can all carry the load simultaneously.  Maybe they don't have to.  Maybe the load shifts between the various force bearing ridges as the coupler parts move around.  I would think the load could not possibly be equalized through all of these solid mechanical stops.  The other interesting point is that, while the knuckle pivot pin does share the load, I believe a pair of couplers would still carry the load if mated together with the knuckle pivot pins missing.
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