Coupling and drawbar standards

[Speedy Builder5Participant @speedybuilder5]

[Speedy Builder5Participant @speedybuilder5]

What standard do we use for coupling heights for a 5" gauge locomotive ?

I see that one standard states 5" above the rail head for ground level track and 4" for raised track (Why the difference ?)

Another standard says 3 1/4" above rail head.

Some standards state 6mm diameter pin, others 4mm.

If I use the 5" standard, the coupling would be above the buffer beam on a SPEEDY Loco 5" gauge.

I am well confused.

Bob

[Dave HalfordParticipant @davehalford22513]

I imagine it's all about club rolling stock coupling height, the extra inch would be due to requiring legs dangling on raised track and therefore everything is lower to the track?

[Peter Seymour-HowellParticipant @peterseymour-howell39349]

As a scale builder, I would follow the GL5 standard of 3 5/8 or near as, there is some leeway in the standard, 5" and 4 " seems strange but then if you are modelling narrow gauge, perhaps not? I'm mainline so not really looked.

Here's the GL5 profile, you'll note that there is a generous amount of leeway, after all, locomotives come in all shapes and sizes.

https://2ebc4dff-5c4b-4001-aa30-16df8083dcc4.filesusr.com/ugd/fbc8da_9a0695dc486642fe8aba2dc028e6aca4.pdf

Pete

[duncan webster 1Participant @duncanwebster1]

SMEE standard says 3+21/32, which is near enough Peter's figure. Don't understand Dave's point at all.

[Speedy Builder5Participant @speedybuilder5]

Thank you gentlemen, I can only imagine that the 5 and 4 inch recommendations came from a club that ran 7 1/4 and 5 inch on the same track line.

Bob

[Perko7Participant @perko7]

Our club has both 7-1/4 and 5 inch gauge locos but all riding cars are 7-1/4 inch gauge with couplings at AALS-regulated height, so all coupling bars need to be at a height to suit, regardless of the loco. Consequently we have a good stock of cranked coupling bars with a wide range of offsets to match various locos to the riding cars.

[duncan webster 1Participant @duncanwebster1]

Cranked coupling bars will have the effect of lifting the back of 5" g locos. I would have though it worth the effort of providing a second set of connections to suit 5"g. If the 7.25" coupling is not central to the 5" loco it will also be trying to derail it

[Speedy Builder5Participant @speedybuilder5]

Yes Duncan, a bit like all cars having the emergency towing eye on one side ?

Tongue in cheek – Bob

[BazyleParticipant @bazyle]

Er, shouldn't the loco and driving truck match, then you have multiple options at the rear of your driving truck. With your weight on the truck it should be stable but maybe consider what happens if you have a small child driving.

[Perko7Participant @perko7]

As Bazyle says, either your weight on the loco tender or on the driving truck would be more than enough to counter any lifting effect from the small difference in coupling height between the loco/driving truck and any towed passenger cars. Our coupling bars are usually 300mm long and the offset or crank is usually less than 10mm so that is about a 1 in 30 offset. The potential uplift force would therefore be less than 3% of the drawbar pull which is usually not more than about 25% of the adhesive weight of the loco. So 3% of 25% is less than 1% of the adhesive weight of the loco. I have not seen any 5 inch locos upset by such a minimal force. Undulations in our track have a greater impact.

We don't have offset coupling pockets on our 7-1/4 riding cars to suit 5 inch locos and have not noticed any increased tendency to derailing. The sideways pull is at an angle of about 1 in 10.7 which generate a sideways force of about 9.5% of the drawbar pull. There is a similar sideways pull when negotiating curves and turnouts and we never have any problems.

Nevertheless, a range of coupling points to suit the locos being used is still a sensible suggestion.

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