Feather Touch Coupling with Knuckle Couplers


I have a "what I did" about improving the coupling of knuckle coupling at:



Thank you if you visit
Do Not Do This!!!

I would advise anyone against doing this for two reasons:

1. The couplers are more prone to lose grip with one another. Many of you may remember the coupler problems I was having several months back with my unit train, where it was prone to random uncouplings after the train stopped or slowed, and then resumed normal speed; there were breaks in the train in several places. Working with Kadee, who worked swiftly to resolve the issue, we narrowed the problem down to there being too much clearance between the thumb of the coupler and the knuckle face. This excess clearance allowed the couplers to "slip away" from each other, or slip out of each other's grip. As freight cars rock back and forth in all axis while travelling, and shift their positions relative to the cars next to them, the coupler bond must be *unbreakable* in all possible relationships so the train will remain coupled.

Bending the thumb of the coupler outward is not a smart idea, as it creates a *weak spot* and opens up a significant gap between thumb and knuckle. When BOTH couplers have that gap, the problem is exacerbated and it isn't hard to find a positioning of the freight cars that will exploit that weakness. With the physical dynamics of how our cars move and shift on the horizontal plane, no matter what the scale, you will almost always find the perfect positioning that will exploit the weakness in this bent thumb coupler idea.

Read the post I linked to above for more information. As it turned out, the problem was that there was too large a gap between the thumb and couplers. (I ordered all of these couplers at the same time, and they all suffered from a Kadee manfacturing flaw that has since been corrected) Harold is essentially recreating the exact couplers that were giving me problems.

2. What's more, bending the plastic thumb will weaken the plastic and, while you may not see any effects immediately, the couplers will eventually give you problems.

There is a reason these couplers were designed the way they were!
1. Looking at your thread the problem was the Kadee #26's the thumb was splayed too much and too short. That is obvious in the pictures. I would have just bent the thumb back. That is why in my article the cars are tested by coupling and rocked back and forth. If they uncouple the thumb is squeezed back to close the gap.

2. The plastic will not break from that little manipulation.

The couplers were designed with an engineering safety factor. That is just being tweaked.

Just a thought

Whether or not the #26 thumb was "splayed too much" or "too short" is a non-issue. It all comes down to there being too much clearance between the thumb and the knuckle, thus allowing a greater amount of room for the claw of the opposing coupler to "escape" the bond. When both couplers are modified (or flawed by manufacture, whatever the case) to increase this clearance, the problem becomes worse. I can tell you this from experience.

It is not my intention to damage your pride here, but I am simply advising anyone reading this to think twice before doing this. A couple of rolls back and forth on a test track may not yield the exact positioning of cars to expose this flaw; only rigorous tests under different weights and speeds on your home layout will prove to green-light this project.

Perhaps for On30, where the cars are larger than HO, this idea may work. However, from personal experience with HO models where the clearance between a coupler's thumb and knuckle was larger than standard, I can relate to you tales of thousands of uncouplings and unreliable coupler bonds.

As I said earlier, Kadee, McHenry, et al manufacture their couplers the way they do for a reason: they are more aware of the various dynamics between the cars than we are, and engineer the couplers to remain coupled under ALL possible circumstances.
Actually using smaller couplers on larger equipment generates problems faster than the opposite. That is why KD's and McHenry's are so much larger than scale.

In fact a few rolls on a test track does reveal that the clearance is too large and the thumb has to be repositioned ever so slightly. There is a position that works.

But is it really worth jeopordizing the operational integrity of the coupler in order to get a "feather touch coupling"? I've never run into problems with Kadee couplers not coupling together, even on a light impact.

Seems like this bent coupler idea opens up a whole new can of worms in order to achieve an easier (really?) coupling.

My $.02
Thus why I'm sticking to the EC87's, no failures like this, just too thin coupler boxes...