Kinematic couplers - design issues.

[woodbury22uk]

Although I am going to link to continental stock this is meant to be a more general question about the design and adequacy of kinematic couplers.

An email from DMToys is linked to an LSModels coach which will go round a 228.6mm (9 inch) curve, but needs a bigger radius (282mm) for an S curve. A 70 euro coach, by the way.

https://www.dm-toys.de/produktdetails/items/LS_78104.html

My understanding of the norm on the  kinematic coupler was that if applied correctly it should extend the distance between vehicles on curves to allow them to run down to a 9 inch curve, and 20 years ago I had Arnold Corail coaches which ran (and still run) just like this in spite of the bogie centres being inset 25mm from the buffers, so creating a lot of end swing on curves, and the individual coaches being 165mm long. This is the design norme NEM 352 in French - no English version as far as I know.

http://www.morop.eu/downloads/nem/fr/nem352_f.pdf

There is a current round of complaints in France about the REE Modelès/Mikado DEV AO coaches where they suffer from buffer lock on curves of any radius but only on some layouts.

So my question is does the norme need to be revised/corrected or are we now seeing designs which do not follow the norme, which is leading to the problem? One suggestion I have read is that whatever the detail of the design the buffers need to be slightly retracted to avoid locking on curves.

From a UK stock perspective I have generally not experienced a problem with kinematic couplers on Farish Mk1s and Dapol Mk 3s, or the Revolution TEAs even after installing shorter couplers to bring the buffers or gangways very close on straights. I usually run a soft pencil around the edges where the moving parts meet to provide a bit of extra slip, and check there is no moulding flash which can easily provoke a snatch in the movement of the coupler arm, and in some cases causes unplanned uncoupling.

Any other experiences?

[Ben A]

Hi Mike,

This is an interesting point.

For Revolution we adopted the kinematic couplers because they improve close coupling (overscale gaps have long been a pet hate of mine) and they work.

However, they do add to the cost and complexity of the model, and as soon as you introduce working parts into any system you also need to consider a maintenance regime.

Your policy of checking for snatching/obstruction and using graphite to lubricate moving parts is probably the kind of thing that all of us should be ready to do to keep things working.

Clearly, a model that works well out of the box may need some TLC after 5, 10 or 15 years.

As to your point about whether the design is fit for purpose, in my experience it is provided the NORMS are adhered to.  My suspicion is that some factories, especially that are not pure "model railway" manufacturers, may cut corners here or there and that can lead to problems.

Cheers

Ben A.

[woodbury22uk]

It may well be that adherence to the Norme and precision of manufacture are the key issues. In the REE Modèles instance I mentioned the buffer faces and gangways faces are aligned across the vehicle and apparently buffer contact takes place on curves - but oddly only on some layouts - which suggests there may be some cleaning up being needed on the mating surfaces. I have the same manufacturers French postal coaches which come with over long couplers as standard. Replacing these with a bar coupling which brings gangways and buffers air hairs breadth apart has not caused an issue although again the buffers and gangways are in exact alignment across the vehicle. They sail through the 9 inch curve on one of the fiddle yard roads. The bar couplers allows them to be propelled through this curve, where the flexibility of shorter individual couplers might result in contact. The norme is specific about having rigid couplers.

[ntpntpntp]

Just shows how out of touch I am - I wasn't aware KKs were fitted to any British N. 

I've yet to have a real problem with any KKs on any brands of continental stock that I run, they all go through my Settrack fiddleyard pointwork fine, but I've also read of a few complaints with some recent releases.  Occasionally I  find one which which doesnt work smoothly without a little fettling and application of graphite.

The worst problem I've had wth KKs is the pesky spring wire going AWOL if the coach is dismantled (usually unintentionally via a trip to the floor!) Not so long ago I bought about a metre of spring steel wire to cut and make my own replacements as-and-when needed.

[woodbury22uk]

The worst problem I've had wth KKs is the pesky spring wire going AWOL if the coach is dismantled (usually unintentionally via a trip to the floor!) Not so long ago I bought about a metre of spring steel wire to cut and make my own replacements as-and-when needed.

I found that a suitable spring replacement was a section of those plastic tags that hold the price labels on to clothes.