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[quote user="Paul_D_North_Jr"] [quote user="Bucyrus"]  [snip]  But when solid contact is made between the force groove and ridge features, the knuckle ceases to be a rotating element, and becomes a linear link, transmitting the pulling force in a straight line like a link of a chain.  Once this function change happens, the pulling force no longer induces the knuckle to rotate.   The rotation of the knuckle and the action of the locking pin together only serve to install or un-install the knuckle as a linear, straight line, pulling link.  The rotation of the knuckle and the action of the locking pin together are not involved with the pulling load.   [/quote]   What Bucyrus wrote above is true only if - pause a moment here to take a look at one of the knuckle top photos above - a straight line can be drawn from the point of application of the pulling force onto the knuckle tip - which would be about where the flag hole is - through the middle of the 'force groove and ridge feature', and into the draft gear, and said line would be parallel to the line of the train.  That would be just about the same as a link in a typical oval-link chain - when pulled on, those links rotate as much as they need to until the points of application of the force on each end of them are in a straight line with the main line of the chain.  No chain under serious tension is ever in a shape other than a straight line - unless there's an interference of some kind along its length.   But a potential interference here is the angle and curve of the 'force groove and ridge feature' at the back end of the coupler tang.  Without knowing exactly how the coupler and the knuckle are fitting together when under load, we can't say for sure whether it's the angled part of the curved part of the grooves and ridges that are carrying the load.  More importantly, the 'line of force' should be at just about a 90 degree angle to the straighter parts, or radial to the curve.  If that isn't the case, then a partial sideways force or 'vector' will be induced by the skewed angle of those grooves and ridges with respect to the perpendicular to the main line of force.  That sideways force will tend to rotate the knuckle - unless it is resisted and restrained by something else, such as either the locking pin, or the sliding friction between all those mating surface areas of the groove and ridge feature.    For the moment, I can see either possibility being valid - Larry and I seem to think it's the first, Bucyrus seems to think it's the second, as I understand it.  Fot those of you who have followed along this far - stay tuned, as in future epsiodes we'll continue to explore the subtle and hidden intricacies of the modern knuckle coupler !  <IMG alt="Big Smile" src="http://cs.trains.com/trccs/emoticons/icon_smile_big.gif">   Bucyrus - you keep up with much more of those detailed explanations, and you'll be ready for a career in technical writing !  <IMG alt="Thumbs Up" src="http://cs.trains.com/trccs/emoticons/icon_smile_thumbsup.gif">   - Paul North. [/quote] Paul, <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p></o:p> I believe that the original Janney coupler did not have the force ridge engagement feature.  Therefore, when under pulling load, that load was transferred to the locking pin and an equal reaction force was transferred to the knuckle pivot pin.  So both the locking pin and the knuckle pivot pin would share the bearing of the full pulling force.  With this coupler, it could not pull a load with the knuckle pivot pin missing.  And also with this coupler, if the locking pin magically disappeared when the coupler was pulling under load the knuckle would open. <o:p></o:p> It would be nice to look at some detailed assembly views to see just how the engagement of the force groove and ridge fall into line with the basic pulling centerline.  Looking at that actual parts or individual part drawings, it is very difficult to visualize because the parts are quite organic in their form.  They almost resemble bone structure of anatomy.  With regard to that centerline, you mentioned that it probably is on the hole in the tip of the knuckle.  Actually when two couplers are coupled, the holes in the tips of their knuckle are not in a line.  They are maybe a couple inches apart.  The pulling centerline would pass midway between them.   <o:p></o:p> I hear what you are saying about the force groove engagement needing to be on the pulling centerline.  That is what I would like to see in a diagram.  It looks like those interlocking groove features would be offset from the centerline, so I don’t know how that would shake out.  I have to think about that some more.  A chain can have bent hooks where part of the hook does not lie on the centerline of pull.   <o:p></o:p> There are two centerlines to consider:  One is the common centerline of the couplers.  The other is the parallel centerline in the pocket of each knuckle where the lobe of the opposing knuckle seats.  That centerline does pass through the hole in the tip of the knuckle, and that centerline may indeed line up with the force groove engagement.  If the force diverted through those centerlines (one for each knuckle), it would amount to a staggered, symmetrical offset to the main centerline of force as it passes through the two coupler heads.      You mentioned that you and Larry see one scenario of operation and I see another.  I am not completely clear about how you see it.  Just remember that whatever scenario you propose, it has to allow the knuckle pin to be removed by hand while a loaded, stretched coupler is under way, and it will not affect the coupling.
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