Scale couplings in 4mm query

[lu4472ke]

I'm thinking about converting my stock to scale couplings but can't see the point of the spring and pin that goes behind the bufferbeam, what purpose does it serve?

[john coffin]

For those of us who were around when steam was on the mainline, this might seem a stupid question, but in fact it is
a reminder that things we took for granted are in fact not well explained.

The spring and split pin are to replicate the movement of the couplings on the prototype particularly when moving
off, or coming to a stock. Many model buffers do not have springs or retract, thus it is important to give the coupling
the ability to move in and out.

In the 1860's many tenders had their couplings attached by springs directly to the locomotive draw bar, generally by
leaf springs, whilst later the leaf springs were at the buffer end. I know this because I have both drawn them, and
inspected some.

Hopefully that answers your request.

Paul

[65447]

Three reasons, one more related to modelling than prototype.

1. To relieve the sudden application of tension as the locomotive draws the train away, especially with loose coupled stock. Adjacent springs compress and allow adjoining items of rolling stock to overcome inertia more progressively. As the train gets under way the springs expand to normal. This action is repeated at both ends of the item of rolling stock and all down the train;

2. To provide a similar smoothing action under differential acceleration, such as when an item of rolling stock accelerates at a different rate to that to which it is coupled - possibly because it is more/less heavily laden or its axleboxes are less/more free running - but then a subsequent brake application by the guard or change of direction over pointwork would make the coupling snatch, with the attendant risk of fracture;

3. Due to the much tighter curves used in model railways, its possible that the buffers could touch on the inside of the curve. If the buffers are not sprung then a derailment is most likely. If the buffers are sprung then, once they are fully compressed, the spring on the coupling hook allows the coupling link to expand and further reduce the risk of derailment.

Earlier rolling stock had a solid bar arrangement connecting both couplings with a spring arrangement at the centre, which transmitted movement to both couplings. Later changes provided for independent springing of the coupling at each end.

[notascoobie]

Hi,

4mm scale rolling stock can't replicate the mass of the real thing so I think the springs and split pins are a waste of space.

I make up the couplings, chemically blacken them then fix them to the wagon. I usually add a bed of plasticard to the underside of the wagon floor so the coupling hook sits level then apply a small amount of epoxy resin to the rear end of the hook shaft. If the hook shaft is too long then I have no qualms in cutting it off.

If you're using exactoscale 3-link couplings, you will find that the wagons will buffer lock on moderate curves. If that's the case replace on of the links with a slightly longer one and/or fix the coupling hook so it's slightly proud of the buffer beam.

But that's just my take, I'm sure there are other views!

Regards,

Vernon

[jwealleans]

I do use the springs and pins, but that's because it leaves the couplings removable. In a few cases, on vehicles with very long buffers, I have reduced the length of the spring then stretched it so there is a little give if needed. I seem to have acquired some softer springs with one lot of couplings, but I don't know where they came from and haven't seen any more recently.

[Hatfield Shed]

4mm scale rolling stock can't replicate the mass of the real thing so I think the springs and split pins are a waste of space...

While very true that the models are nothing like the mass, or more significantly have only a fraction of the inertia of the prototype due to the far lower absolute velocity; even so if you operate anything like full size trains of 4W wagons, the springs make a difference in track holding if there is any deviation from smooth action. Even at these low energies a collision or snatch in a train with all rigidly fixed components will often have a wagon or two off. With a good proportion of the drawhooks sprung and a few sprung buffer sets distributed along the train, such shocks are dissipated and damped out without derailment.

In my operation the superb regulation provided by DCC has made this provision less necessary, but it still matters when a fault or accident causes a short which the DCC system detects and trips the track power. It's very convenient when 45 of fitted goods making a scale 50mph behind a V2 on a concealed curve all stay on the rails in such an event. Not to speak of human errors when shunting or changing engines, I am so adept at leaving locos and stock fouling running lines.