Using Ed’s illustration from earlier in the thread, I might buy somewhat into your premise, Bucyrus, but keeping the knuckle closed will require constant tension. Without the locking pin in place, even momentary slack will cause the coupler to open when pressure is applied to the bearing face. Your premise also assumes that there is enough friction between the grooves and slots within the coupler to prevent it from rotating under load.
Note that the bearing face of the knuckle is not in line with the pivot point. The offset is enough that the locking pin does not have to bear the full load, but the offset also guarantees that if any force is applied to the bearing face (sans locking pin), the knuckle will pivot.
I will tell you that it doesn’t take a lot of stretch to keep the pin from lifting, thus it doesn’t take much slack to cut it loose.
I agree that the instant the slack begins to run in, the knuckle bind-up will be lost, and the kuckle will open upon re-stretch if there is no locking pin in place.
As I mentioned, I do not know whether my conclusion about the locking pin not being needed when the couplers are stretched is true or not. However, there is something about what this thread has revealed so far that drives me to that conclusion. That is the fact that the knuckle pin serves no load transmitting function, but rather is only there to keep the knuckle from falling out. It would be logical to conclude that the pulling load tries to open the knuckle, the locking pin prevents that opening, and so the locking pin is bearing a dynamic force that rises as the pulling load rises.
However: If you pull on the knuckle and that pull induces it to rotate, and the locking pin counteracts that rotation force, then there must be a reaction force back to the knuckle pivot pin. And yet the knuckle pin carries no load.
If you look at the lock pin, you can see it is keyed, shaped in such a manner that when in the down position, it prevent the knuckle from rotating, lifted, it allows the knuckle tang to slide on the grooves, and the knuckle opens…but also note, although it is not shown, that the lock pin is almost totally encased inside the solid coupler body…the small amount of “play” in the knuckle never allows enough of an impact to shear this lock…it is about 2 inches thick both ways…even though thousands of tons of force are applied to it, just like a bolt or rivet in a structure, because there is little if any “play” in it the force is transmitted to the knuckle and coupler…trust me, remove the lock pin and the knuckle will open…you can replace a knuckle and the lock pin with zero tools…that said, with the way the rear of the tang is designed, if the knuckle was always under constant tension, (slack out) and some how the lock pin was removed, it is possible the lands and grooves in the tang would hold the knuckle in place…but the first little bit of slack and it would open.
To clairify some,…the knuckle pin is the pin the knuckle rotates on, it bears little if any load witht he knuckle closed…the lock pin is the device located behind the knuckle tang that locks the knuckle into the coupler body…it is load bearing, the rotational force of the knuckle under tension is applied to it and the straight line directional force to the tang lands and grooves.
No promises, but I will try and get some photos tomorrow to explain…
I didn’t mean to re-start all the analysis, but now that we are here again…
I think that the angle of the large ridges (2/2A and 3/3A in my photos on page 4 of this thread above) is enough so that stretching forces (along the tracks) create considerable force at the forward end of the tang on the knuckle towards the right (as you face forward) against the lock, even though there may be some sticking between the ridges. I don’t think any sticking between the ridges would be anywhere near enough to inhibit the knuckle from opening. Therefore a stretching force will open the knuckle when the lock is raised out of the way.
I think that the reaction force (reaction to the force towards the right against the lock) is a force towards the left from ridges 2 and 3 against ridges 2A and 3A. And those same ridges carry most of the stretching force.
In addition, with the knuckle closed, ridges 1/1A and 4/4A carry any load in the location of the knuckle pin. OTOH, with the knuckle in the open position, ridge 1 is not in contact with ridge 1A and ridge 2 is not in contact with ridge 2A; and the knuckle pin is the only thing holding the knuckle to the coupler.
I think we are picking up exactly where we left off. I always had kind of a lingering feeling that there were a couple issues left unresolved. I want to think more about your above quote, but in the meantime, consider this:
In lieu of a graphic diagram, consider a clock face and compass directions for reference to the knuckle movement:
As to the action, here’s a really simplistic drawing. I am no artiste.
The left image represents an open knuckle (kinda). As I understand it, the lock pin will be riding on top of the knuckle body (I was a little off…). When the knuckle pivots on the pin, the lock pin drops in at the notch, as noted by the red dot representing the lock pin.
Obviously there will be variations, but this covers the basics.
You’ll notice that there will have to be a certain amount of force exerted on the locking pin, but that the lever distances make that force relatively insignificant compared to the total force being held by the coupler.
Here’s that “open” coupler, with some parts labelled. If I mis-named anything, fire away!
I see only 4 different locking pins - 2 for Type E couplers, and 2 for Type F couplers. And among those, 1 of each is for the top, and the other is for the bottom. I presume that designation means for where the cut lever/ rod is located - on top or underneath the coupler itself, per the previous posts, such as in rotary couplers on unit trains, etc.
But now, after seeing those diagrams - and in partial response to the latest debate about whether the coupler knuckle would open when under load if the locking pin were removed, etc. - let me ask this:
What is the function of the ‘knuckle thrower’ ? I presume that when the locking pin is lifted, it moves the knuckle thrower to push and rotate the knuckle to the open position. So if the locking pin was removed, there’d be nothing to motivate the knuckle thrower. But since the knuckle thrower is most likely for the purpose of and designed to open the knuckle when there is nothing attached to the coupler, in that circumstance the knuckle thrower may be superfluous and unncessary - the pull on the coupler from the next car may be enough to open the knuckle, even without a knuckle thrower. So I suppose the debate can continue on . . . [:-,] [:-^]
In theory, the knuckle thrower is going to keep my tootsies off the coupler itself, and therefore me out of the guage. Yes, it’s mainly going to apply when opening a coupler which is not attached to another coupler.
If you’re pulling two couplers apart, the unopened coupler will pull open the one you’ve pulled the pin on…
THIS IS OBSOLETE EXPLANATION. REPLACED BY REVISED EXPLANATION PAGE 13, 9/1/09
Here is my analysis of the coupler function as clearly as I can express it:
On a single coupler with an open knuckle, the knuckle is loosely attached to the coupler body by the knuckle pin, and the knuckle’s force groove is swung out of alignment with the corresponding force ridge on the coupler body.
When the knuckle is closed, the locking pin drops into position, and the knuckle’s force groove comes into alignment with the corresponding force ridge on the coupler body. At this point the knuckle fits loosely with its pivot pin, with the locking pin, and in the relationship between its force groove and the corresponding ridge on the coupler body.
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. Th
Another way to look at it that occurs to me is to think of the main part of the coupler as a box, closed on four sides (top, bottom, left, rear, as you face the coupler). The front of the box is such that the closed knuckle can’t be pulled out (rather like pulling on the pointy part of a nail that’s been driven through a board - the head keeps it from coming through). That leaves the right side of the box open - and it is effectively closed by the locking pin.
As Bucyrus opines, the force ridges keep the knuckle from pulling out, while the other five “sides” of the box hold the knuckle in place.
In a purely straight-line pull, those five sides are of little import. Add any variables (slack, run-in, curves, irregular track) and they become most important.
Yes, I’m ignoring the rotary component of the knuckle movement.
I want to congratulate all you gentlemen for the excellent discourse on this topic. As I read, I cannot believe how hard it is to explain. I can still vividly recall when a mixed train conductor explained how it worked to my Dad and me when I was ten years old. Even then, I was surprised that my Dad had never really understood the intricacies of it, and at that point he had been working for the CPR for 17 years. It is an amazing aggregation of simple parts utilizing simple concepts doing an incredible amount of work.
It truly is something that needs to be seen in operation to be understood. I’ve been thinking that Larry or Carl needs to invite all of the non railroader forum members to their jobsites to show us how it works. Then Paul and Bucyrus can really give us a good explanation.
What sticks out in my mind even yet, is how the various ages and conditions of the couplers can still pull together. I’ve seen pre-WWI era MOW equipment hooked to ancient combine passenger cars, to WWI era cabooses, to the newest rolling stock available from the manufacturer.
In Paul’s post above I am going to have to give the nod to both of Paul’s conclusions, because as one part of the coupler wears out another component seems to step up and take its’ place. Until age or load, or both, causes the inevitable failure.
Take a good look at the “pivot point” provided by the knuckle pin and note where it is in relationship to the lock pin and kuckle tang…it is to the left and forward of the center line, not quite in the middle of the knuckle so the needed leverage or rotation created when you pull on the knuckle is pretty large (you gotta give it a pretty gool pull to open it by hand because your pulling on the short leg of a lever)…so the force against the lock pin is small…as Bucyrus pointed out, once the slack is taken up, most of the force is applied to the lands and grooves of the knuckle and the coupler body…only a small amount of force is trying to rotate the knuckle because of the design of the knuckle inner faces when they are mated and closed and locked, the rest of the force is straight lined through the knuckle faces and the coupler bodys, to the drawbars and drawbar keepers and then the car center sill.
And the reason the knuckle thrower or hook works when you lift the cut lever is because the thrower is pushing on the back side of the LONG leg of the lever created by the knuckle riding on the knuckle pin.
The design of the lock pin pushes the thrower when you lift the pin (lock) with the cut lever, which is a long lever lifting a short pin, it creates a lot of leverage, and the thrower only pushes so far anyway…inerita finishes the task of opening the knuckle, once you get 50 +lbs of steel moving it tends to keep moving, and if the knuckle pin(pivot) or the knuckle is worn, you end up having to reach in and pull the knuckle open the rest of the way.
The reason for the thrower is simple, there are times you don’t want you hand in there, as when cars are close to each other, but static…and you are not sure if there is something like anothe
