OO Gauge Fixed Link Coach Couplings – Part 1

At long last my freight couplings for British OO rolling stock with NEM sockets are now available, so it’s time to share with you my designs for coach couplings.  You can find the freight couplings here.

Early British coaches had similar coupling to the freight 3 link.  They each had a hook and a chain, but because passenger stock needs to be smooth, the chains had a screw section in the middle. This worked by having the locomotive push two coaches together so the buffers compressed, then the chain was hooked over the hook and the screw tightened up.  When the locomotive releases the pressure the buffers can never fully un-spring.  This means there’s never any slack which would cause the train to snatch and jerk, as that’s not ideal when you’re sitting down to lunch!  Below is an example of a locomotive coupled to a coach with a screw link coupling.

Later coach stock adopted the knuckle coupler, very similar to the standard system used in the US. The difference is the knuckle can rotate around the hook so both systems could be used.  The knuckle coupler would hang down allowing normal access to the hook.  When needed, the knuckle coupler was lifted and held in place by a pin.  In the picture below you can see this arrangement on a BR Mk 1 coach. (Picture by Chris McKenna from Wikipedia)

The pin also held the knuckle down when not in use to prevent it from swinging.  This has also been implemented on locomotives.  You can see it on the front of the BR Class 91 locomotive below. (Picture by Chris McKenna from Wikipedia).

Modeling this can done and, with newer models now having the NEM sockets, different couplings can easily be exchanged.  A plug-in Kadee knuckle coupler is available for the NEM socket and it’s a good way to connect coaches.  However as with the freight stock, if you have rakes of coaches which you want to stay permanently coupled, adding Kadee couplers comes with the risk of separation plus the expense of adding one to each end of every coach.  Bachmann make a coupling designed to be a fixed link between coaches which looks like vacuum pipes hanging down.  Again this is a good idea but what if you run trains at exhibitions or like to swap the trains on your layout?  Picking up 5 to 10 coaches all linked together is a bit tricky.

So how is 3D printing a coupler better than this?  Well, the nice thing about coach stock is they normally have a corridor connection so travelers can move from coach to coach; this hides the coupling.  Therefore the coupling doesn’t have to represent anything, it simply needs to work.

My coupling is just that, simple.

Each has a peg and hole at one end and the NEM fitting at the other.  The two couplers simply overlap.  The height of the peg ensures they won’t come uncoupled but when you want to remove the coach from the layout you simply pick it up.

As with the freight rolling stock different manufactures have placed their NEM sockets in different locations causing the gap between coaches to vary.  This gap will also need to be specific to your layout depending on the radius of your curves.  So to solve this I have made a few options in length.

And unlike the freight couplings there are only a few; five different types in fact.

They can be used in pairs with the same number or mixed together to give any required length.

Next week I’ll share more with you regarding these couplings and some images of them in use.